4,5-SECO-4,6-CYCLOSTEROIDS .3. OBSERVATIONS ON COURSE OF REDUCTIVE REARRANGEMENT OF 6BETA-BROMO-4BETA,5-EPOXY-5BETA-CHOLESTAN-3BETA-OL

It has been shown that reductive rearrangement of 6β-bromo-4β,5-epoxy-5β-cholestan-3β-ol (I) to 4,5-seco-4,6-cycle-6β-cholestane-3β,5α-diol (IXa) with lithium aluminium hydride in tetrahydrofuran proceeds via 6β-bromo-5β-cholestane-3β,5-diol (IIa). Relevant reactions of the latter and the corresponding 3-ketone are discussed. Similar conversion of the 3-epimer of (I) into 4,5-seco-4,6-cyclo-6β-cholestane-3α,5α-diol (XIIIa) in high yield indicates that reductive rearrangement of the 6β-bromo-5β-hydroxy moiety proceeds without participation of the 3-aluminate complex. Some derivatives of (XIIIa) are described. Experimental conditions required for the conversion of (I) into (IXa) are defined. Combined evidence indicates that the reaction proceeds in a concerted manner by essentially base-catalysed, 1,3-elimination of hydrogen bromide from diol (IIa) with 4,5-bond migration to give the formal intermediate 3β-hydroxy-4,5-seco-4,6-cyclo-6β-cholestan-5-one (VI), further reduced to (IXa). © 1969, CSIRO. All rights reserved.