Add time:07/30/2019         Source:sciencedirect.com

The structure of 13-ethyl-11-methylene-18,19-dinor-17α-pregn-4-en-20-yn-16β,17-diol (3, 16β-OH desogestrel), a by-product obtained in the last step of the synthesis of desogestrel (1) by reaction of monolithium acetylide-ethylenediamine complex with 13β-ethyl-11-methylenegon-4-en-17-one (2), is here reported. The structural assignments were supported by NMR 1H-, 13C-, 1H-1H COSY, 1H-13C HSQC, COLOC) and mass spectroscopy, and the configuration at the C-16 and C-17 stereocentres was established by X-ray crystallography. When the same 17-ketoderivative 2 was treated with a non-alkylating base, such as potassium tert-butoxide, instead of the expected 16-hydroxylated ketone, a dimeric product, 13β-ethyl-16-[2′-(des-D-13″-carboxy-13″β-ethyl-11″-methylenegon-4″-en-14″-yl)-ethyliden]-11-methylenegon-4-en-17-one (4), was isolated in good yield; it was characterized by NMR, mass, ultaviolet spectroscopy, and chemical transformations. Compounds 3 and 4 originate from the high reactivity of the 16-methylenic position of the 17-keto substrate (2) toward molecular oxygen under basic conditions.

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