Some stereoselective and regioselective olefin additions: iodoacetoxylation and related electrophilic additions across the 22(23)-bond of 3α,5α-cycloergosta-7,22-dien-6-one
Abstract
Iodoacetoxylation of the 22(23)-olefinic bond of 3α,5α-cycloergosta-7,22-dien-6-one proceeds in a stereoselective and regioselective manner; reactions with other electrophilic reagents proceed similarly. The structures of the adducts have been correlated chemically, by measurements of molecular rotation differences for the derived 22- and 23-alcohols, and by an X-ray crystallographic analysis of (23R)-23-hydroxy-3α,5α-cycloergost-7-en-6-one. Whereas lithium aluminium hydride reduction of the 23-ketone obtained from the latter alcohol proceeded according to the Cram rule, reduction of the corresponding 22-ketone did not. These results allow the stereoselective preparation of 22- and 23-hydroxy-steroids.
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