Abstract
Alkylation of 3,17β-bis(2-trimethylsilyl)ethoxymethyl-1,3,5(10) estratriene-6-one ( 2 ) with 5-bromo-1-pentene using NaHMDS in THF afforded 3,17β-bis(2-trimethylsilyl)ethoxymethyl-7-α-(4′-pentenyl)-1,3,5(10)estratriene-6-one ( 3 ) in excellent stereoselectivity (>95% epimeric excess). Functionalization of the side chain in compound 3 was accomplished via ozonolysis, oxidation and esterification to give 5 in 72% yield. The reduction of ester ( 5 ) using NaBH 4 in MeOH afforded the corresponding 6α-hydroxy compound ( 6 ) as a single isomer in 72% yield. The hydroxyl group in 6 was removed by converting to the corresponding xanthate ( 7 ) followed by reduction using n- Bu 3SnH to afford 8 in good yield. Finally, the SEM protective groups in 8 were removed, after which the ester function was hydrolyzed with LiOH to give 7α-(3′-carboxypropyl)estradiol ( 10 ), in 10.6% overall yield from 3 .
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