The cyclization of tetrahydropyran (I) with 2-butylacrolein (II) by means of K2CO3 at 110 C gives the spirodipyran (III), which is epoxidated with dimethyldioxirane in dichloromethane yielding the epoxide (IV). The rearrangement of (IV) by means of camphorsulfonic acid (CSA) affording the carbaldehyde (V), which is condensed with lithium trimethylsilylacetylene (VI) affording carbinol (VII) with incorrect stereochemistry. The oxidation of (VII) with DMP in dichloromethane providing the ketone (VIII), which is reduced with L-Selectride to the carbinol (IX) with the correct stereochemistry. The treatment of (IX) with K2CO3 in MeOH eliminates the trimethylsilyl group giving the acetylene (X), which is silylated at the OH group with TBDMS-OTf and lutidine in dichloromethane yielding (XI). The selective desilylation of (XI) with HF穚yr in THF affords the primary alcohol (XII), which is oxidated with DMP in dichloromethane affording the aldehyde (VIII). The Wittig condensation of (XIII) with phosphorane (XIV) in hot chlorobenzene furnishes the aldehyde (XV).

A new Wittig condensation of aldehyde (XV) with phosphorane (XVI) in refluxing benzene gives the diunsaturated ester (XVII), which is reduced with DIBAL to the corresponding alcohol, and oxidated with DMP yielding the aldehyde (XVIII). The condensation of (XVIII) with the chiral propionyloxazolidinethione (XIX) by means of Sn(OTf)2 and 1-ethylpiperidine in dichloromethane affords the adduct (XX), which is treated with NaBH4 in THF to eliminate the chiral auxiliary and afford diol (XXI). The metalation of (XXI) with Bu3SnH and a Pd catalyst gives the vinylstannane (XXII), which is desilylated with TBAF in THF yielding the trihydroxycompound (XXIII). The condensation of stannane (XXIII) with iodobutenoic ester (XXIV) by means of a Pd catalyst affords the diunsaturated ester (XXV), which is selectively disilylated with TBDMSCl and imidazole in hot DMF to provide the disilyl ether (XXVI).

The esterification of the secondary OH group of (XXVI) with acid (XXVII) by means of DCC and DMAP gives the corresponding ester (XXVIII), which is selectively desilylated with HF/pyridine in THF giving the primary alcohol (XXIX). The oxidation of (XXIX) with DMP in pyridine/THF yields the corresponding aldehyde (XXX), which by a new Wittig condensation with phosphorane (XXXI) in dichloromethane affords the fully silylated precursor (XXXII). Finally this compound is desilylated by a treatment with TBAF in DMF.

The cyclization of tetrahydropyran (I) with 2-butylacrolein (II) by means of K2CO3 at 110 C gives the spirodipyran (III), which is epoxidated with dimethyldioxirane in dichloromethane yielding the epoxide (IV). The rearrangement of (IV) by means of camphorsulfonic acid (CSA) affording the carbaldehyde (V), which is condensed with lithium trimethylsilylacetylene (VI) affording carbinol (VII) with incorrect stereochemistry. The oxidation of (VII) with DMP in dichloromethane providing the ketone (VIII), which is reduced with L-Selectride to the carbinol (IX) with the correct stereochemistry. The treatment of (IX) with K2CO3 in MeOH eliminates the trimethylsilyl group giving the acetylene (X), which is silylated at the OH group with TBDMS-OTf and lutidine in dichloromethane yielding (XI). The selective desilylation of (XI) with HF穚yr in THF affords the primary alcohol (XII), which is oxidated with DMP in dichloromethane affording the aldehyde (VIII). The Wittig condensation of (XIII) with phosphorane (XIV) in hot chlorobenzene furnishes the aldehyde (XV).

A new Wittig condensation of aldehyde (XV) with phosphorane (XVI) in refluxing benzene gives the diunsaturated ester (XVII), which is reduced with DIBAL to the corresponding alcohol, and oxidated with DMP yielding the aldehyde (XVIII). The condensation of (XVIII) with the chiral propionyloxazolidinethione (XIX) by means of Sn(OTf)2 and 1-ethylpiperidine in dichloromethane affords the adduct (XX), which is treated with NaBH4 in THF to eliminate the chiral auxiliary and afford diol (XXI). The metalation of (XXI) with Bu3SnH and a Pd catalyst gives the vinylstannane (XXII), which is desilylated with TBAF in THF yielding the trihydroxycompound (XXIII). The condensation of stannane (XXIII) with iodobutenoic ester (XXIV) by means of a Pd catalyst affords the diunsaturated ester (XXV), which is selectively disilylated with TBDMSCl and imidazole in hot DMF to provide the disilyl ether (XXVI).

The esterification of the secondary OH group of (XXVI) with acid (XXVII) by means of DCC and DMAP gives the corresponding ester (XXVIII), which is selectively desilylated with HF/pyridine in THF giving the primary alcohol (XXIX). The oxidation of (XXIX) with DMP in pyridine/THF yields the corresponding aldehyde (XXX), which by a new Wittig condensation with phosphorane (XXXI) in dichloromethane affords the fully silylated precursor (XXXII). Finally this compound is desilylated by a treatment with TBAF in DMF.

The condensation of 3-(tert-butyldimethylsilyloxy)propanal (XXXIII) with the chiral borane (XXXIV) by means of H2O2 and NaHCO3 gives the chiral alcohol (XXXV), which is oxidized with OsO4 and NaIO4 to yield the aldehyde (XXXVI). The Wittig condensation of (XXXVI) with phosphorane (XVI) affords the heptenoic ester (XXXVII), which is reduced with H2 over Pd/C to provide the saturated hydroxy ester (XXXVIII). The cyclization of (XXXVIII) by means of PPTS in refluxing dichloromethane gives the lactone (XXXIX), which by reaction with Cp2TiMe2 yields the methylene derivative (I).