This compound is prepared by several related ways: 1) The reaction of silylated azetidinone (I) with tetrahydrofuran-2-thiocarboxylic acid (II) by means of NaOH in THF - water gives the azetidinone thioester (III), which is condensed with allyl glyoxylate in refluxing benzene yielding the hydroxyester (IV). The reaction of (IV) with SOCl2 affords the chloroester (V), which by reaction with triphenylphosphine by means of lutidine in hot THF is converted into the phosphoranylidene derivative (VI). The elimination of the silyl protecting group of (VI) with tetrabutylammonium fluoride gives the azetidinone (VII), which is cyclized in refluxing toluene yielding the (5R,6S)-6-[1(R)-hydroxyethyl]-2-[2(R)-tetrahydrofuryl]penem-3-carboxyli c acid allyl ester (VIII). Finally, this compound is hydrolyzed with triphenylphosphine, sodium 2-ethylhexanoate and Pd-tetrakis(triphenylphosphine). 2) The condensation of the silver salt of protected azetidinone (IX) with tetrahydrofuran-2(R)-carbonyl chloride (X) also yields the phosphoranylidene salt (VI). 3) Phosphoranylidene ester (VI) can also be cyclized first in refluxing benzene yielding the silylated penem ester (XI), which is deprotected with tetrabutylammonium fluoride to (VIII). 4) The hydrolysis of allyl ester (VIII) to the final product can also be performed with paladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethylacetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether. 5) The preceding hydrolysis can also be performed with triphenylphosphine and paladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanyl-azetidinone (II), which is converted into the silver salt (III) by reaction with AgNO3. Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) -- obtained by treatment of carboxylic acid (V) with thionyl chloride -- providing the azetidinone thioester (VI). Coupling of azetidinone (VI) with allyl oxalyl chloride (VII) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene, affords penem (VIII). Alternatively, compound (VIII) can also be obtained as follows: Substitution of phenyl sulfonyl group of azetidinone (X) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (XI), which is condensed with allyl oxalyl chloride (VII) by means of DIEA in CH2Cl2 to give the oxalyl amide (XII). Compound (XII) is then treated with AgNO3 and pyridine in acetonitrile, providing the silver mercaptide (XIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIV). Penem (VIII) is obtained by intramolecular Wittig cyclization of (XIV) with P(OEt)3 in refluxing xylene. Finally, faropenem sodium can be obtained by removal of the tbdms protecting group of (VIII) by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and HOAc in THF to give compound (IX). This is followed by allyl ester group removal of (IX), which can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; or iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanylazetidinone (II), which by reaction with AgNO3 is converted into the silver salt (III). Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) ?obtained by treatment of carboxylic acid (V) with thionyl chloride ?to provide the azetidinone thioester (VI). Alternatively, compound (VI) can be obtained by condensation of tetrahydrofuran-2(R)-thiocarboxylic S-acid (VII) ?obtained by treatment of carboxylic acid (V) with hydrogen sulfide ?with silylated azetidinones (I) or (VIII) by means of NaOH in THF/water. Condensation of azetidinone thioester (VI) with allyl glyoxylate (IX) in refluxing benzene gives the hydroxy ester (X), which is treated with SOCl2 to yield the chloro ester (XI). Reaction of compound (XI) with triphenylphosphine and lutidine in hot THF provides the phosphoranylidene derivative (XII), which is converted into (5R,6S)-6-[1(R)-hydroxyethyl]-2-[2(R)-tetrahydrofuryl]penem-3-carboxylic acid allyl ester, faropenem allyl ester (XIII) by removal of the silyl protecting group with tetrabutylammonium fluoride, followed by cyclization in refluxing toluene. Compound (XII) can also be obtained by condensation of the silver salt of protected azetidinone (XIV) with tetrahydrofuran-2(R)-carbonyl chloride (V).

Alternatively, faropenem allyl ester (XIII) can also be prepared by cyclization of compound (XII) in refluxing benzene to yield silylated penem allyl ester (XV), which is then deprotected with either tetrabutylammonium fluoride in AcOH or triethylamine tris(hydrogen fluoride) in methyl isobutyl ketone or toluene. Penem (XV) can also be synthesized by several related ways: a) By coupling of azetidinone (VI) with allyl oxalyl chloride (XVI) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene. b) Substitution of phenyl sulfonyl group of azetidinone (VIII) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (II), which is condensed with allyl oxalyl chloride (XVI) by means of DIEA in CH2Cl2 to give the oxalyl amide (XVII). Compound (XVII) is then treated with AgNO3 and pyridine in acetonitrile to provide the silver mercaptide (XVIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIX). Finally, compound (XV) is obtained by intramolecular Wittig cyclization of (XX) with P(OEt)3 in refluxing xylene.

Hydrolysis of faropenem allyl ester (XIII) to faropenem sodium (XX) can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)- 5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; and iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF. Finally, faropenem daloxate can be directly obtained from faropenem sodium (XX) by esterification with 4-(iodomethyl)-5-methyl-1,3-dioxol-2-one (XXI) in DMF.

Hydrolysis of faropenem allyl ester (XIII) to faropenem sodium (XX) can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)- 5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; and iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF. Finally, faropenem daloxate can be directly obtained from faropenem sodium (XX) by esterification with 4-(iodomethyl)-5-methyl-1,3-dioxol-2-one (XXI) in DMF.

This compound is prepared by several related ways: 1) The reaction of silylated azetidinone (I) with tetrahydrofuran-2-thiocarboxylic acid (II) by means of NaOH in THF - water gives the azetidinone thioester (III), which is condensed with allyl glyoxylate in refluxing benzene yielding the hydroxyester (IV). The reaction of (IV) with SOCl2 affords the chloroester (V), which by reaction with triphenylphosphine by means of lutidine in hot THF is converted into the phosphoranylidene derivative (VI). The elimination of the silyl protecting group of (VI) with tetrabutylammonium fluoride gives the azetidinone (VII), which is cyclized in refluxing toluene yielding the (5R,6S)-6-[1(R)-hydroxyethyl]-2-[2(R)-tetrahydrofuryl]penem-3-carboxyli c acid allyl ester (VIII). Finally, this compound is hydrolyzed with triphenylphosphine, sodium 2-ethylhexanoate and Pd-tetrakis(triphenylphosphine). 2) The condensation of the silver salt of protected azetidinone (IX) with tetrahydrofuran-2(R)-carbonyl chloride (X) also yields the phosphoranylidene salt (VI). 3) Phosphoranylidene ester (VI) can also be cyclized first in refluxing benzene yielding the silylated penem ester (XI), which is deprotected with tetrabutylammonium fluoride to (VIII). 4) The hydrolysis of allyl ester (VIII) to the final product can also be performed with paladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethylacetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether. 5) The preceding hydrolysis can also be performed with triphenylphosphine and paladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanyl-azetidinone (II), which is converted into the silver salt (III) by reaction with AgNO3. Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) -- obtained by treatment of carboxylic acid (V) with thionyl chloride -- providing the azetidinone thioester (VI). Coupling of azetidinone (VI) with allyl oxalyl chloride (VII) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene, affords penem (VIII). Alternatively, compound (VIII) can also be obtained as follows: Substitution of phenyl sulfonyl group of azetidinone (X) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (XI), which is condensed with allyl oxalyl chloride (VII) by means of DIEA in CH2Cl2 to give the oxalyl amide (XII). Compound (XII) is then treated with AgNO3 and pyridine in acetonitrile, providing the silver mercaptide (XIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIV). Penem (VIII) is obtained by intramolecular Wittig cyclization of (XIV) with P(OEt)3 in refluxing xylene. Finally, faropenem sodium can be obtained by removal of the tbdms protecting group of (VIII) by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and HOAc in THF to give compound (IX). This is followed by allyl ester group removal of (IX), which can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; or iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF.

Hydrolysis of faropenem allyl ester (XIII) to faropenem sodium (XX) can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)- 5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; and iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF. Finally, faropenem daloxate can be directly obtained from faropenem sodium (XX) by esterification with 4-(iodomethyl)-5-methyl-1,3-dioxol-2-one (XXI) in DMF.

This compound is prepared by several related ways: 1) The reaction of silylated azetidinone (I) with tetrahydrofuran-2-thiocarboxylic acid (II) by means of NaOH in THF - water gives the azetidinone thioester (III), which is condensed with allyl glyoxylate in refluxing benzene yielding the hydroxyester (IV). The reaction of (IV) with SOCl2 affords the chloroester (V), which by reaction with triphenylphosphine by means of lutidine in hot THF is converted into the phosphoranylidene derivative (VI). The elimination of the silyl protecting group of (VI) with tetrabutylammonium fluoride gives the azetidinone (VII), which is cyclized in refluxing toluene yielding the (5R,6S)-6-[1(R)-hydroxyethyl]-2-[2(R)-tetrahydrofuryl]penem-3-carboxyli c acid allyl ester (VIII). Finally, this compound is hydrolyzed with triphenylphosphine, sodium 2-ethylhexanoate and Pd-tetrakis(triphenylphosphine). 2) The condensation of the silver salt of protected azetidinone (IX) with tetrahydrofuran-2(R)-carbonyl chloride (X) also yields the phosphoranylidene salt (VI). 3) Phosphoranylidene ester (VI) can also be cyclized first in refluxing benzene yielding the silylated penem ester (XI), which is deprotected with tetrabutylammonium fluoride to (VIII). 4) The hydrolysis of allyl ester (VIII) to the final product can also be performed with paladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethylacetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether. 5) The preceding hydrolysis can also be performed with triphenylphosphine and paladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanyl-azetidinone (II), which is converted into the silver salt (III) by reaction with AgNO3. Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) -- obtained by treatment of carboxylic acid (V) with thionyl chloride -- providing the azetidinone thioester (VI). Coupling of azetidinone (VI) with allyl oxalyl chloride (VII) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene, affords penem (VIII). Alternatively, compound (VIII) can also be obtained as follows: Substitution of phenyl sulfonyl group of azetidinone (X) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (XI), which is condensed with allyl oxalyl chloride (VII) by means of DIEA in CH2Cl2 to give the oxalyl amide (XII). Compound (XII) is then treated with AgNO3 and pyridine in acetonitrile, providing the silver mercaptide (XIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIV). Penem (VIII) is obtained by intramolecular Wittig cyclization of (XIV) with P(OEt)3 in refluxing xylene. Finally, faropenem sodium can be obtained by removal of the tbdms protecting group of (VIII) by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and HOAc in THF to give compound (IX). This is followed by allyl ester group removal of (IX), which can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; or iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF.

Alternatively, faropenem allyl ester (XIII) can also be prepared by cyclization of compound (XII) in refluxing benzene to yield silylated penem allyl ester (XV), which is then deprotected with either tetrabutylammonium fluoride in AcOH or triethylamine tris(hydrogen fluoride) in methyl isobutyl ketone or toluene. Penem (XV) can also be synthesized by several related ways: a) By coupling of azetidinone (VI) with allyl oxalyl chloride (XVI) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene. b) Substitution of phenyl sulfonyl group of azetidinone (VIII) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (II), which is condensed with allyl oxalyl chloride (XVI) by means of DIEA in CH2Cl2 to give the oxalyl amide (XVII). Compound (XVII) is then treated with AgNO3 and pyridine in acetonitrile to provide the silver mercaptide (XVIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIX). Finally, compound (XV) is obtained by intramolecular Wittig cyclization of (XX) with P(OEt)3 in refluxing xylene.

Hydrolysis of faropenem allyl ester (XIII) to faropenem sodium (XX) can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)- 5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; and iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF. Finally, faropenem daloxate can be directly obtained from faropenem sodium (XX) by esterification with 4-(iodomethyl)-5-methyl-1,3-dioxol-2-one (XXI) in DMF.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanyl-azetidinone (II), which is converted into the silver salt (III) by reaction with AgNO3. Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) -- obtained by treatment of carboxylic acid (V) with thionyl chloride -- providing the azetidinone thioester (VI). Coupling of azetidinone (VI) with allyl oxalyl chloride (VII) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene, affords penem (VIII). Alternatively, compound (VIII) can also be obtained as follows: Substitution of phenyl sulfonyl group of azetidinone (X) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (XI), which is condensed with allyl oxalyl chloride (VII) by means of DIEA in CH2Cl2 to give the oxalyl amide (XII). Compound (XII) is then treated with AgNO3 and pyridine in acetonitrile, providing the silver mercaptide (XIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIV). Penem (VIII) is obtained by intramolecular Wittig cyclization of (XIV) with P(OEt)3 in refluxing xylene. Finally, faropenem sodium can be obtained by removal of the tbdms protecting group of (VIII) by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and HOAc in THF to give compound (IX). This is followed by allyl ester group removal of (IX), which can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; or iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF.

Alternatively, faropenem allyl ester (XIII) can also be prepared by cyclization of compound (XII) in refluxing benzene to yield silylated penem allyl ester (XV), which is then deprotected with either tetrabutylammonium fluoride in AcOH or triethylamine tris(hydrogen fluoride) in methyl isobutyl ketone or toluene. Penem (XV) can also be synthesized by several related ways: a) By coupling of azetidinone (VI) with allyl oxalyl chloride (XVI) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene. b) Substitution of phenyl sulfonyl group of azetidinone (VIII) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (II), which is condensed with allyl oxalyl chloride (XVI) by means of DIEA in CH2Cl2 to give the oxalyl amide (XVII). Compound (XVII) is then treated with AgNO3 and pyridine in acetonitrile to provide the silver mercaptide (XVIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIX). Finally, compound (XV) is obtained by intramolecular Wittig cyclization of (XX) with P(OEt)3 in refluxing xylene.

Treatment of 4-(chloromethyl)-5-methyl-1,3-dioxol-2-one (XXII) with potassium formate (XXIII) by means of KI and NaHCO3 in DMF affords the formyloxymethyl derivative (XXIV), which is converted into the hydroxymethyl derivative (XXV) by refluxing in MeOH. Coupling of compound (XXV) with oxalyl chloride (XXVI) in dichloromethane furnishes compound (XXVII), which is then condensed with protected azetidinone (VI) by means of Et3N in dichloromethane to yield compound (XXVIII). Intramolecular Wittig cyclization of compound (XXVIII) by means of triethyl phosphite in refluxing xylene provides the silylated faropenem daloxate (XXIX), which is finally deprotected by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and AcOH in THF.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanyl-azetidinone (II), which is converted into the silver salt (III) by reaction with AgNO3. Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) -- obtained by treatment of carboxylic acid (V) with thionyl chloride -- providing the azetidinone thioester (VI). Coupling of azetidinone (VI) with allyl oxalyl chloride (VII) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene, affords penem (VIII). Alternatively, compound (VIII) can also be obtained as follows: Substitution of phenyl sulfonyl group of azetidinone (X) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (XI), which is condensed with allyl oxalyl chloride (VII) by means of DIEA in CH2Cl2 to give the oxalyl amide (XII). Compound (XII) is then treated with AgNO3 and pyridine in acetonitrile, providing the silver mercaptide (XIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIV). Penem (VIII) is obtained by intramolecular Wittig cyclization of (XIV) with P(OEt)3 in refluxing xylene. Finally, faropenem sodium can be obtained by removal of the tbdms protecting group of (VIII) by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and HOAc in THF to give compound (IX). This is followed by allyl ester group removal of (IX), which can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; or iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF.

Hydrolysis of faropenem allyl ester (XIII) to faropenem sodium (XX) can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)- 5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; and iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF. Finally, faropenem daloxate can be directly obtained from faropenem sodium (XX) by esterification with 4-(iodomethyl)-5-methyl-1,3-dioxol-2-one (XXI) in DMF.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanyl-azetidinone (II), which is converted into the silver salt (III) by reaction with AgNO3. Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) -- obtained by treatment of carboxylic acid (V) with thionyl chloride -- providing the azetidinone thioester (VI). Coupling of azetidinone (VI) with allyl oxalyl chloride (VII) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene, affords penem (VIII). Alternatively, compound (VIII) can also be obtained as follows: Substitution of phenyl sulfonyl group of azetidinone (X) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (XI), which is condensed with allyl oxalyl chloride (VII) by means of DIEA in CH2Cl2 to give the oxalyl amide (XII). Compound (XII) is then treated with AgNO3 and pyridine in acetonitrile, providing the silver mercaptide (XIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIV). Penem (VIII) is obtained by intramolecular Wittig cyclization of (XIV) with P(OEt)3 in refluxing xylene. Finally, faropenem sodium can be obtained by removal of the tbdms protecting group of (VIII) by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and HOAc in THF to give compound (IX). This is followed by allyl ester group removal of (IX), which can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; or iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF.

Treatment of 4-(chloromethyl)-5-methyl-1,3-dioxol-2-one (XXII) with potassium formate (XXIII) by means of KI and NaHCO3 in DMF affords the formyloxymethyl derivative (XXIV), which is converted into the hydroxymethyl derivative (XXV) by refluxing in MeOH. Coupling of compound (XXV) with oxalyl chloride (XXVI) in dichloromethane furnishes compound (XXVII), which is then condensed with protected azetidinone (VI) by means of Et3N in dichloromethane to yield compound (XXVIII). Intramolecular Wittig cyclization of compound (XXVIII) by means of triethyl phosphite in refluxing xylene provides the silylated faropenem daloxate (XXIX), which is finally deprotected by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and AcOH in THF.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanyl-azetidinone (II), which is converted into the silver salt (III) by reaction with AgNO3. Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) -- obtained by treatment of carboxylic acid (V) with thionyl chloride -- providing the azetidinone thioester (VI). Coupling of azetidinone (VI) with allyl oxalyl chloride (VII) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene, affords penem (VIII). Alternatively, compound (VIII) can also be obtained as follows: Substitution of phenyl sulfonyl group of azetidinone (X) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (XI), which is condensed with allyl oxalyl chloride (VII) by means of DIEA in CH2Cl2 to give the oxalyl amide (XII). Compound (XII) is then treated with AgNO3 and pyridine in acetonitrile, providing the silver mercaptide (XIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIV). Penem (VIII) is obtained by intramolecular Wittig cyclization of (XIV) with P(OEt)3 in refluxing xylene. Finally, faropenem sodium can be obtained by removal of the tbdms protecting group of (VIII) by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and HOAc in THF to give compound (IX). This is followed by allyl ester group removal of (IX), which can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; or iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanylazetidinone (II), which by reaction with AgNO3 is converted into the silver salt (III). Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) ?obtained by treatment of carboxylic acid (V) with thionyl chloride ?to provide the azetidinone thioester (VI). Alternatively, compound (VI) can be obtained by condensation of tetrahydrofuran-2(R)-thiocarboxylic S-acid (VII) ?obtained by treatment of carboxylic acid (V) with hydrogen sulfide ?with silylated azetidinones (I) or (VIII) by means of NaOH in THF/water. Condensation of azetidinone thioester (VI) with allyl glyoxylate (IX) in refluxing benzene gives the hydroxy ester (X), which is treated with SOCl2 to yield the chloro ester (XI). Reaction of compound (XI) with triphenylphosphine and lutidine in hot THF provides the phosphoranylidene derivative (XII), which is converted into (5R,6S)-6-[1(R)-hydroxyethyl]-2-[2(R)-tetrahydrofuryl]penem-3-carboxylic acid allyl ester, faropenem allyl ester (XIII) by removal of the silyl protecting group with tetrabutylammonium fluoride, followed by cyclization in refluxing toluene. Compound (XII) can also be obtained by condensation of the silver salt of protected azetidinone (XIV) with tetrahydrofuran-2(R)-carbonyl chloride (V).

Hydrolysis of faropenem allyl ester (XIII) to faropenem sodium (XX) can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)- 5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; and iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF. Finally, faropenem daloxate can be directly obtained from faropenem sodium (XX) by esterification with 4-(iodomethyl)-5-methyl-1,3-dioxol-2-one (XXI) in DMF.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanyl-azetidinone (II), which is converted into the silver salt (III) by reaction with AgNO3. Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) -- obtained by treatment of carboxylic acid (V) with thionyl chloride -- providing the azetidinone thioester (VI). Coupling of azetidinone (VI) with allyl oxalyl chloride (VII) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene, affords penem (VIII). Alternatively, compound (VIII) can also be obtained as follows: Substitution of phenyl sulfonyl group of azetidinone (X) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (XI), which is condensed with allyl oxalyl chloride (VII) by means of DIEA in CH2Cl2 to give the oxalyl amide (XII). Compound (XII) is then treated with AgNO3 and pyridine in acetonitrile, providing the silver mercaptide (XIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIV). Penem (VIII) is obtained by intramolecular Wittig cyclization of (XIV) with P(OEt)3 in refluxing xylene. Finally, faropenem sodium can be obtained by removal of the tbdms protecting group of (VIII) by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and HOAc in THF to give compound (IX). This is followed by allyl ester group removal of (IX), which can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; or iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF.

Alternatively, faropenem allyl ester (XIII) can also be prepared by cyclization of compound (XII) in refluxing benzene to yield silylated penem allyl ester (XV), which is then deprotected with either tetrabutylammonium fluoride in AcOH or triethylamine tris(hydrogen fluoride) in methyl isobutyl ketone or toluene. Penem (XV) can also be synthesized by several related ways: a) By coupling of azetidinone (VI) with allyl oxalyl chloride (XVI) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene. b) Substitution of phenyl sulfonyl group of azetidinone (VIII) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (II), which is condensed with allyl oxalyl chloride (XVI) by means of DIEA in CH2Cl2 to give the oxalyl amide (XVII). Compound (XVII) is then treated with AgNO3 and pyridine in acetonitrile to provide the silver mercaptide (XVIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIX). Finally, compound (XV) is obtained by intramolecular Wittig cyclization of (XX) with P(OEt)3 in refluxing xylene.

Hydrolysis of faropenem allyl ester (XIII) to faropenem sodium (XX) can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)- 5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; and iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF. Finally, faropenem daloxate can be directly obtained from faropenem sodium (XX) by esterification with 4-(iodomethyl)-5-methyl-1,3-dioxol-2-one (XXI) in DMF.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanyl-azetidinone (II), which is converted into the silver salt (III) by reaction with AgNO3. Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) -- obtained by treatment of carboxylic acid (V) with thionyl chloride -- providing the azetidinone thioester (VI). Coupling of azetidinone (VI) with allyl oxalyl chloride (VII) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene, affords penem (VIII). Alternatively, compound (VIII) can also be obtained as follows: Substitution of phenyl sulfonyl group of azetidinone (X) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (XI), which is condensed with allyl oxalyl chloride (VII) by means of DIEA in CH2Cl2 to give the oxalyl amide (XII). Compound (XII) is then treated with AgNO3 and pyridine in acetonitrile, providing the silver mercaptide (XIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIV). Penem (VIII) is obtained by intramolecular Wittig cyclization of (XIV) with P(OEt)3 in refluxing xylene. Finally, faropenem sodium can be obtained by removal of the tbdms protecting group of (VIII) by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and HOAc in THF to give compound (IX). This is followed by allyl ester group removal of (IX), which can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)-5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; or iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF.

Alternatively, faropenem allyl ester (XIII) can also be prepared by cyclization of compound (XII) in refluxing benzene to yield silylated penem allyl ester (XV), which is then deprotected with either tetrabutylammonium fluoride in AcOH or triethylamine tris(hydrogen fluoride) in methyl isobutyl ketone or toluene. Penem (XV) can also be synthesized by several related ways: a) By coupling of azetidinone (VI) with allyl oxalyl chloride (XVI) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene. b) Substitution of phenyl sulfonyl group of azetidinone (VIII) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (II), which is condensed with allyl oxalyl chloride (XVI) by means of DIEA in CH2Cl2 to give the oxalyl amide (XVII). Compound (XVII) is then treated with AgNO3 and pyridine in acetonitrile to provide the silver mercaptide (XVIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIX). Finally, compound (XV) is obtained by intramolecular Wittig cyclization of (XX) with P(OEt)3 in refluxing xylene.

Treatment of the silylated azetidinone (I) with tritylmercaptan affords the tritylsulfanylazetidinone (II), which by reaction with AgNO3 is converted into the silver salt (III). Compound (III) is coupled with tetrahydrofuran-2(R)-carbonyl chloride (IV) ?obtained by treatment of carboxylic acid (V) with thionyl chloride ?to provide the azetidinone thioester (VI). Alternatively, compound (VI) can be obtained by condensation of tetrahydrofuran-2(R)-thiocarboxylic S-acid (VII) ?obtained by treatment of carboxylic acid (V) with hydrogen sulfide ?with silylated azetidinones (I) or (VIII) by means of NaOH in THF/water. Condensation of azetidinone thioester (VI) with allyl glyoxylate (IX) in refluxing benzene gives the hydroxy ester (X), which is treated with SOCl2 to yield the chloro ester (XI). Reaction of compound (XI) with triphenylphosphine and lutidine in hot THF provides the phosphoranylidene derivative (XII), which is converted into (5R,6S)-6-[1(R)-hydroxyethyl]-2-[2(R)-tetrahydrofuryl]penem-3-carboxylic acid allyl ester, faropenem allyl ester (XIII) by removal of the silyl protecting group with tetrabutylammonium fluoride, followed by cyclization in refluxing toluene. Compound (XII) can also be obtained by condensation of the silver salt of protected azetidinone (XIV) with tetrahydrofuran-2(R)-carbonyl chloride (V).

Alternatively, faropenem allyl ester (XIII) can also be prepared by cyclization of compound (XII) in refluxing benzene to yield silylated penem allyl ester (XV), which is then deprotected with either tetrabutylammonium fluoride in AcOH or triethylamine tris(hydrogen fluoride) in methyl isobutyl ketone or toluene. Penem (XV) can also be synthesized by several related ways: a) By coupling of azetidinone (VI) with allyl oxalyl chloride (XVI) in CH2Cl2 by means of Et3N, followed by intramolecular Wittig cyclization by means of triethyl phosphite in refluxing xylene. b) Substitution of phenyl sulfonyl group of azetidinone (VIII) by tritylmercaptan by means of NaOH in acetone/water provides tritylsulfanyl-azetidinone (II), which is condensed with allyl oxalyl chloride (XVI) by means of DIEA in CH2Cl2 to give the oxalyl amide (XVII). Compound (XVII) is then treated with AgNO3 and pyridine in acetonitrile to provide the silver mercaptide (XVIII), which is acylated with tetrahydrofuran-2(R)-carbonyl chloride (IV) in acetonitrile to afford the penem precursor (XIX). Finally, compound (XV) is obtained by intramolecular Wittig cyclization of (XX) with P(OEt)3 in refluxing xylene.

Hydrolysis of faropenem allyl ester (XIII) to faropenem sodium (XX) can be performed under several different conditions: i) triphenylphosphine, sodium 2-ethylhexanoate and palladium tetrakis(triphenylphosphine); ii) palladium tetrakis(triphenylphosphine) and sodium 4-(methoxycarbonyl)- 5,5-dimethylcyclohexane-1,3-dione enolate in several different solvents such as methyl acetate, ethyl acetate, tetrahydrofuran, dioxane, sec-butanol, acetonitrile, acetone, 2-butanone, 1,2-dichloroethane, chlorobenzene, toluene, or ethylene glycol dimethyl ether; iii) triphenylphosphine and palladium tetrakis(triphenylphosphine) with sodium propionate, sodium acetate or sodium lactate in tetrahydrofuran or acetone; and iv) palladium acetate in the presence of P(OBu)3 and sodium propionate in THF. Finally, faropenem daloxate can be directly obtained from faropenem sodium (XX) by esterification with 4-(iodomethyl)-5-methyl-1,3-dioxol-2-one (XXI) in DMF.

Treatment of 4-(chloromethyl)-5-methyl-1,3-dioxol-2-one (XXII) with potassium formate (XXIII) by means of KI and NaHCO3 in DMF affords the formyloxymethyl derivative (XXIV), which is converted into the hydroxymethyl derivative (XXV) by refluxing in MeOH. Coupling of compound (XXV) with oxalyl chloride (XXVI) in dichloromethane furnishes compound (XXVII), which is then condensed with protected azetidinone (VI) by means of Et3N in dichloromethane to yield compound (XXVIII). Intramolecular Wittig cyclization of compound (XXVIII) by means of triethyl phosphite in refluxing xylene provides the silylated faropenem daloxate (XXIX), which is finally deprotected by means of either Et3N tris(hydrogen fluoride) in ethyl acetate or tetrabutylammonium fluoride (TBAF) and AcOH in THF.