Abstract
(3S,15R)-15-(Benzyloxy)-3-[(tert-butyldimethylsilyl)oxy]-17-iodoandrosta-5,16-diene (3) was prepared from the corresponding 17-hydrazone9with iodine in the presence of tetramethylguanidine. The vinyl iodide3was converted into the corresponding organocuprate and conjugate additions of the latter were performed with both (E)- and (Z)-6-methylhept-2-en-4-one (4aand4b, respectively). In each case, the resulting adduct5awas obtained exclusively with the unnatural 20Sconfiguration. (3S,15R)-15-(Benzyloxy)-3-[(tert-butyldimethylsilyl)oxy]androsta-5,16-diene (13) and the corresponding 17,17' homocoupling product14were obtained as byproducts. When the addition to theE-enone was repeated in the presence of chloro(trimethyl)silane, the yield of the conjugate addition product improved, but the stereochemistry at C-20 remained the same.
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