Synthesis of a medium-size ring via alkoxy radical decomposition

Abstract

Conversion of cholestane-3β,5α-diol 3-acetate into two ten-membered ring ketones, 5,10-secocholest-trans- and 5,10-secocholest-cis-1(10)-en-3β-ol-5-one acetates, via alkoxy radical intermediates is described, and the stereochemistry of these ketones is discussed. It is shown that acid-catalysed rearrangement of the trans-ketone gives 7α-methylene-A, 19-bisnor-B-homo-10β-cholestane-2β,5α-diol 2-acetate. In the course of this work a remarkable hydrogen bonding between an hydroxyl group and a suitably located double bond has been observed. Some interesting observations on the reduction of cholestan-5α-ol-3-one with sodium borohydride and lithium aluminium hydride and also recorded.