D.N. Kirk

Reaction of epoxides—XI : A novel “backbone rearrangement” of the cholestane skeleton

Abstract Purified BF3-etherate reacts with 3β-acetoxy-5,6α-epoxy-5α-cholestane(I) at high concentrations in benzene to give the unsymmetrical di-steroidal ether (IIa). The formation of the ether (IIa) involves a novel “backbone rearrangement” of one of the steroidal skeletons, giving the 5β,14β-dimethyl 18,19-bisnor structure with all ring junction configurations inverted. 3,3-Ethylene dioxy-5,6β-epoxy-5β-cholestane reacts with BF3-etherate to give the rearranged monomeric product (IVd), among other products. 3β,5,6β-Triacetoxy-5α-cholestane undergoes a similar “backbone” shift on treatment with BF3-etherate in acetic anhydride at 80°.

Reactions of epoxides—V : Rearrangements of 5,6-epoxy-6-methyl-cholestanes with boron trifluoride ☆

Abstract 5,6,α-Epoxy-6β-methyl-5α-cholestane, like its 3β-acetoxy derivative, undergoes rearrangement with boron trifluoride to give the 5β-methyl-A-homo-B-nor-4a-ketone. The 3-deoxy-4a-ketone, however, undergoes a further rearrangement with boron trifluoride to give 5-methyl-5β-cholestan-6-one. 3β-Acetoxy-5,6β-epoxy-6α-methyl-5β-cholestane reacts rapidly with boron trifluoride to give a fluorohydrin, which suffers a slower rearrangement to give both the 5β-methyl-A-homo-B-nor-4a-ketone and 3β-acetoxy-5-methyl-5α-cholestan-6-one. In contrast, the 3-deoxy 5β,6β-epoxide gives 6-methyl-cholesta-3,5-diene, 5-acetyl-B-nor-5β-cholestane, and 5-methyl-5α-cholestan-6-one.

Acid catalysed reactions of 5α-hydroxy-steroids—III : The westphalen rearrangement☆

A kinetic study of the Westphalen rearrangement has revealed that the reaction proceeds through a sulphate ester which gives rise to a C5 carbonium ion. The effect of the 6β-substituent on the course of the reaction is described.

Reactions of epoxides—II : Rearrangements of 3-acetoxy-4,5-epoxycholestanes with boron trifluoride

Abstract 3β-Acetoxy-4α,5-epoxy-5α-cholestane is rearranged by boron trifluoride to give 3β-acetoxy-5β-cholestan-4-one (IV). Under similar reaction conditions the 3α-acetox-4β,5β-epoxide gives a stable 3α,5α-bridged ionic complex, and the 3β-acetoxy-4β,5β epoxide gives the fluorohydrin (X).

Reactions of epoxides—VI : A conformational analysis of rearrangements of tetra-substituted epoxides☆

Abstract A conformational analysis of the rearrangements of a model 1,2-dialkyl-epoxycyclohexane with BF 3 suggests two possible modes of cleavage of the epoxide to give carbonium ions which may subsequently rearrange to form ketones. “Axial cleavage” of the epoxide is defined, and shown to be preferred over “equatorial cleavage” by a conformational analysis of rearrangements of twelve steroidal epoxides.

Reactions of epoxides—I : Rearrangements of some 3-substituted 4,5-epoxy-4-methylcholestanes with boron trifluoride

Abstract The epimeric 4,5-epoxides derived from 4-methylcholest-4-en-3-one and 3α- and 3β-acetoxy-4-methylcholest-4-enes have been rearranged with boron trifluoride. Each of the six epoxides exhibits its own distinctive pattern of behaviour.

Reactions of epoxides—VII : Acid-catalysed reactions of 13,17a-epoxy-and 17a,18-epoxy-C-nor-D-homo-spirostans

Abstract New preparative routes to the 13α,17aα-epoxide (II) and the 13β,17aβ-epoxide (III) are described. Boron trifluoride in benzene converts the α-epoxide (II) into a mixture from which five products were isolated, but the β-epoxide (III) gives only the 17aβ-hydroxy-Δ8(14)-olefin (VIII). Both epoxides give fluorohydrins with boron trifluoride in ether. The 17aα,18-epoxide (X) reacts with either boron trifluoride or perchloric acid to give mainly the 18-aldehyde (XII). The 17aβ,18-epoxide give a variety of products under different reaction conditions.

Reactions of 5α-hydroxy stereoids—VII : The westphalen rearrangement of some 3β-substituted-6β-acetoxy-5α-hydroxy cholestanes☆

Abstract Product analyses and kinetic studies of the reactions of 3β-substituted-6β-acetoxy-5α-hydroxy cholestanes with H 2 SO 4 -Ac 2 O-AcOH reveal a marked dependence of the reactions upon the nature of the 3β-substituent.

Reactions of epoxides—XIV : The preparation and some reactions of the 12,12′-epoxy-derivatives of 12-methylene-tigogenin☆

Abstract Contrary to earlier reports, the reaction between methylmagnesium bromide and hecogenin gives predominantly the 12α-hydroxy-12β-methyl derivative, and epoxidation of 12-methylenetigogenin gives the 12α,12′- and 12β,12′-epoxides in ratio 2:1. The reactions of these epoxides with both boron trifloride and aqueous perchloric acid have been studied.

Reactions of epoxides—IV : The rearrangements of 4α,5α- and 4β,5β-epoxy-4-methyl-cholestanes with boron trifluoride, and a novel ketone rearrangement☆

Abstract 4β,5β-Epoxy-4α-methylcholestane undergoes rearrangement with boron trifluoride to give mainly 5-methyl-5α-cholestan-4-one. Under similar conditions the 4α,5α-epoxide gives the 5β-methyl-A-nor-B-homo-6-ketone (VI), which rearranges on prolonged treatment with boron trifluoride to give 5-methyl-5β-cholestan-4-one.