Convergent Synthesis of Vitamin D3 Metabolites. Control of the Stereoselectivity in Samarium-Induced Cyclopropanations of Cyclopentenes
摘要:
The 25-hydroxy and 1 alpha,25-dihydroxy vitamin D-3 metabolites are obtained by solvolytic rearrangements of the 1-desoxy and 1 alpha-hydroxy cyclopropyl vinylogous alcohols 31 and 29, respectively, with simultaneous formation of the vitamin D structural triene and the 3-hydroxy function. Two complementary methods have been employed to direct the stereoselectivity ofthe samarium induced olefin cyclopropanations which ultimately lead to key chiral ring A precursors. One protocol uses the two stereogenic centers of the (R,R)-B,S-butanediol ketal moiety of 8, while the other method uses the allylic hydroxyl group of(R)-16.
Enantiocomplementary preparation of optically pure 2-trimethylsilylethynyl-2-cyclopentenol by homochiralization of racemic precursors: a new route to the key intermediate of 1,25-dihydroxycholecalciferol and vincamine
摘要:
Treatment of racemic 2-trimethylsilylethynyl-2-cyclopentenol [(+/-)-1] with vinyl acetate in the presence of lipase PS in toluene yielded a 1:1 mixture of the unreacted (S)-alcohol [(S)-1] and the (R)-acetate [(R)-7] which without isolation afforded the chirally homogeneous (R)-alcohol [(R)-1] in 73% overall yield on reaction with acetic acid in the same reaction medium in the presence of diisopropyl azodicarboxylate and triphenylphosphine, followed by reductive deacylation of the resulting (R)-acetate [(R)-7]. On the other hand, hydrolysis of the racemic acetate [(+/-)-7], obtained from [(+/-)-1], in a phosphate buffer solution in the presence of lipase PS yielded a 1:1 mixture of the (R)-alcohol [(R)-1] and the unreacted (S)-acetate [(S)-7] which without separation, furnished the enantiomerically homogeneous (S)-alcohol [(S)-1] in 75% overall yield on treatment with acetic acid under the above Mitsunobu conditions, followed by reductive deacylation of the resulting (S)-acetate [(S)-7].
The first and asymmetric total synthesis of rubriflordilactone A, a bisnortriterpenoid isolated fromSchisandrarubriflora, has been accomplished in a convergent manner. Two enantioenriched fragments were forged together to give a functionalized cis-triene. A 6π-electrocyclization/aromatization sequence assembled the penta-substituted arene, and a formal vinylogous Mukaiyama aldol reaction introduced
1,25-Dihydroxycholecalciferol (23) was synthesized from A-ring precursor 18 and Windaus-Grundmann ketone 19 via cyclovitamin D 21. Key reactions include highly stereoselective (5 to 6) and stereospecific (13 to 14) cyclopropanations.
Convergent Synthesis of Vitamin D<sub>3</sub> Metabolites. Control of the Stereoselectivity in Samarium-Induced Cyclopropanations of Cyclopentenes
作者:M. M. Kabat、J. Kiegiel、N. Cohen、K. Toth、P. M. Wovkulich、M. R. Uskoković
DOI:10.1021/jo951229d
日期:1996.1.1
The 25-hydroxy and 1 alpha,25-dihydroxy vitamin D-3 metabolites are obtained by solvolytic rearrangements of the 1-desoxy and 1 alpha-hydroxy cyclopropyl vinylogous alcohols 31 and 29, respectively, with simultaneous formation of the vitamin D structural triene and the 3-hydroxy function. Two complementary methods have been employed to direct the stereoselectivity ofthe samarium induced olefin cyclopropanations which ultimately lead to key chiral ring A precursors. One protocol uses the two stereogenic centers of the (R,R)-B,S-butanediol ketal moiety of 8, while the other method uses the allylic hydroxyl group of(R)-16.
Enantiocomplementary preparation of optically pure 2-trimethylsilylethynyl-2-cyclopentenol by homochiralization of racemic precursors: a new route to the key intermediate of 1,25-dihydroxycholecalciferol and vincamine
作者:Seiichi Takano、Mahito Suzuki、Kunio Ogasawara
DOI:10.1016/s0957-4166(00)80151-2
日期:1993.5
Treatment of racemic 2-trimethylsilylethynyl-2-cyclopentenol [(+/-)-1] with vinyl acetate in the presence of lipase PS in toluene yielded a 1:1 mixture of the unreacted (S)-alcohol [(S)-1] and the (R)-acetate [(R)-7] which without isolation afforded the chirally homogeneous (R)-alcohol [(R)-1] in 73% overall yield on reaction with acetic acid in the same reaction medium in the presence of diisopropyl azodicarboxylate and triphenylphosphine, followed by reductive deacylation of the resulting (R)-acetate [(R)-7]. On the other hand, hydrolysis of the racemic acetate [(+/-)-7], obtained from [(+/-)-1], in a phosphate buffer solution in the presence of lipase PS yielded a 1:1 mixture of the (R)-alcohol [(R)-1] and the unreacted (S)-acetate [(S)-7] which without separation, furnished the enantiomerically homogeneous (S)-alcohol [(S)-1] in 75% overall yield on treatment with acetic acid under the above Mitsunobu conditions, followed by reductive deacylation of the resulting (S)-acetate [(S)-7].