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.
Control of stereoselectivity in samarium metal induced cyclopropanations. Synthesis of 1,25-dihydroxycholecalciferol
摘要:
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.
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.