title: [3,3]-Claisen rearrangements in 24alpha-methyl steroid synthesis. Application to campesterol, crinosterol, and Delta25-crinosterol side chain construction.
abstract: This paper elaborates an improved synthesis of crinosterol and campesterol starting from stigmasterol. The proposed approach is based on Claisen rearrangement of Delta23-22-allylic alcohols with various configurations of the 22-hydroxy group and geometry of the Delta23-double bond. It allows complete use of the starting steroid for preparing 24alpha-methyl derivatives. It was possible to partially control the stereochemistry at C-25. Hydrogenation of the Delta22-double bond was shown to proceed with partial isomerization of the C-24 alkyl substituent. The Ireland ester enolate variant of the Claisen rearrangement was demonstrated to be useful for preparing 24alpha-methyl steroids containing the Delta22,25-system.
authors: Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, Kuprevich str., 5/2, 220141 Minsk, Belarus. khripach@iboch.bas-net.by
authors: Vladimir A
authors: VA
authors: Khripach
authors: Vladimir N
authors: VN
authors: Zhabinskii
authors: Olga V
authors: OV
authors: Konstantinova
authors: Natalya B
authors: NB
authors: Khripach
authors: Andrey P
authors: AP
authors: Antonchick
authors: Bernd
authors: B
authors: Schneider
mesh_terms: D000438:Alcohols / Q000737:chemistry; D002784:Cholesterol / Q000031:analogs & derivatives* / Q000737:chemistry*; D015394:Molecular Structure; D010840:Phytosterols; D013256:Steroids / Q000138:chemical synthesis*; D013261:Sterols / Q000737:chemistry*
chemical_list: D000438:Alcohols; D010840:Phytosterols; D013256:Steroids; D013261:Sterols; C467539:crinosterol; C021273:campesterol; D002784:Cholesterol