The Grignard reaction of vinyloxirane (I) with phenylmagnesium bromide and CuCN in THF gives 4-phenyl-2-buten-1-ol (II), which is submitted to a Sharpless epoxidation with t-BuOOH and Ti(Oi-Pr)4 in dichloromethane in the presence of (-)-diethyl tartrate [(-)-DET] yielding the chiral epoxide (III). The reaction of (III) with Ti(Oi-Pr)2(N3)2 in refluxing benzene affords the 3(S)-azido-4-phenylbutane-1,2(S)-diol (IV), which is epoxidized with 2-acetoxy-2-methylpropionyl chloride (A) and NaOMe in THF to give the chiral azidoepoxide (V). The reaction of (V) with isobutylamine (VI) in hot isopropanol yields the secondary amine (VII), which is condensed with 4-methoxyphenylsulfonyl chloride (VIII) in pyridine affording the sulfonamide (IX). The reduction of the azido group of (IX) with H2 over Pd/C in methanol provides (X) with a primary amino group that is finally condensed with the succinimidinyl carbonate (XI) by means of triethylamine in acetonitrile.
The intermediate succinimidinyl carbonate (XI) has been obtained as follows: The reaction of 2,3-dihydrofuran (XII) with N-iodosuccinimide (NIS) and propargyl alcohol (XIII) in dichloromethane gives trans-3-iodo-2-(propargyloxy)tetrahydrofuran (XIV), which is cyclized by means of Bu3SnH and AIBN in hot toluene yielding the methylenic compound (XV). The ozonolysis of (XV) with O3, followed by reduction with NaBH4 in ethanol affords the racemic alcohol (XVI), which is submitted to an enantioselective acylation with Ac2O and lipase 30 to obtain the chiral alcohol (3R,3aS,6aR)-(XVI). Finally, this compound is treated with disuccinimidinyl carbonate and triethylamine in acetonitrile to provide the target intermediate (XI).
The mixed carbonate ester intermediate (X) has been obtained as follows: The reaction of dihydrofuran (I) with propargyl alcohol (II) and N-iodosuccinimide (NIS) gives the propargyl ether (III), which is cyclized by means of tributyltin hydride and AIBN in refluxing toluene to yield the perhydrofuro[2,3-b]furan (IV). The oxidation of the methylene group of (IV) with ozone in methanol/dichloromethane affords the bicyclic ketone (V), which is reduced with NaBH4 in ethanol to provide racemic (VI). The digestion of (rac)-(VI) with immobilized lipase 30 and acetic anhydride in DME provides a mixture of the (3R)-alcohol (VII) and the (3S)-acetoxy derivative (VIII) that is separated by chromatography. Finally, the (3R)-(VII) alcohol is condensed with disuccinimidyl carbonate (IX) and TEA in acetonitrile to give the target mixed carbonate ester intermediate (X).
The reaction of butadiene monooxide (XI) with phenylmagnesium bromide (XII) and CuCN in THF gives trans-4-phenyl-2-buten-1-ol (XIII), which is enantioselectively epoxidated with Ti(O-iPr)4, diethyl D-tartrate and tBu-OOH to yield the (2R,3R)-epoxide (XIV). The reaction of (XIV) with Ti(O-iPr)4 and N3-SiMe3 in refluxing benzene affords the chiral azidodiol (XV), which is epoxidated by means of 2-acetoxyisobutyryl chloride (AcBCl) and NaOMe in THF to provide the chiral azidoepoxide (XVI) (1). Opening of the epoxide ring of (XVI) with isobutylamine (XVII) in hot isopropanol gives the secondary amine (XVIII), which is acylated with 4-aminophenylsulfonyl chloride (XIX) and pyridine in dichloromethane to yield the corresponding sulfonamide (XX). The reduction of the azido group of (XX) with H2 over Pd/C in THF/methanol/HOAc affords the expected primary amine (XXI), which is finally condensed with the already reported intermediate (X) in dichloromethane to provide the target carbamate.