Synthesis of steroid 24,20-lactones by means of phenylselenolactonization

✍ Scribed by Marian Kocòr; Beata Bersz

• Book ID: 104203048
• Publisher: Elsevier Science
• Year: 1985
• Tongue: French
• Weight: 720 KB
• Volume: 41
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(01)83486-4

✦ Synopsis

A synthesis of (20 R)-and (20 S)-3/3-methoxy-S-cholen-24,20_lactones (7s and 7b) from 3/?methoxy-5-androsten-lFone(2)isdescribedThe l7-ketone2wastreated withisopropenyllithium togive3/Imethoxy-l7~-(propl'-en-2'-ylo~5-androsten-l7/%ol

(3). Compound 3 on reaction with ethyl orthoacetate and Claisen rearrangement of intermediate 17p-orthoester furnished ethyl esters of (E)and (Z)-3/L methoxy-chol-5,17(20)diene-24-acids (4b and 4a). Hydrolysis of ester groups in 4a and 4b and phenylselenolactonization afforded stereospecifically and regioselectively unsaturated (20 RF and (20 S)-3/?methoxy-chol-5,16-diene-24,2~lactones(6s and 6b), respectively. Reduction ofdouble bond 16-17 in 6~ and Qbgave the final products'la and7b.Thephenylselenolactonizaation of(E)-and(Z)-3/Lmethoxy-chol-5,17(20)diene-24-acids (5b and 51) and spontaneous elimination of phenylselenyl moiety was investigated and compared with iodolactonization of the same unsaturated acids.