Synthesis of 3,4-13C2-steroids

A-ring enollactones la, lb, or 9 derived from 4-cholesten-3-one, testosterone benzoate or 3-oxo-4-estren-17 beta-yl benzoate were condensed with [1,2-13C2]acetyl chloride to give intermediates 2a, 2b, or 10. 2a and 2b were cyclized by acid or base to give 3,4 13c-labeled 4-cholesten-3-one and testosterone, respectively. [3,4-13c2 14-Cholesten-3-one was converted via reduction of its trimethylsilyl enol ether to [3,4-13C2] cholesterol. Acetyl enollactone 10 was cyclized in acetic acid to [3,4-13c2] 3-oxo-4-estren-17beta-yl benzoate followed by aromatization and hydrolysis to produce ]3,4-13c2] estradiol-17 beta. Alternatively, cyclization of 10 with base afforded [3,4-13c2-oxo-4-estren-17 beta-ol directly, which was then oxidized and aromatized to yield ]3,4-13c2] estrone. Ozonolysis of progesterone, conversion to the diketal ester 16 and acylation followed by acid hydrolysis furnished [3,4-13c2] progesterone.