Synthetic steroids. Part X. Preparation of (3S)- and (3R)-spiro-[5α-cholestane-3,2′-oxiran] and their corresponding 2α-methyl and 2,2-dimethyl analogues
作者:J. D. Ballantine、P. J. Sykes
DOI:10.1039/j39700000731
日期:——
The preparation is reported of the 3R- and 3S-forms of spiro-[5α-cholestane-3,2′-oxiran] and their 2α-methyl and 2,2-dimethyl derivatives. The six epoxides were synthesised by addition of methylene to the relevant 3-ketone with either dimethylsulphoxonium methylide or dimethylsulphonium methylide, or by peroxidation of the corresponding 3-methylene-steroid with either m-chloroperoxybenzoic acid or
The BF3-catalysed rearrangements of exocyclic methylene epoxides at C-3, C-6, C-7 and C-12 give mixtures of epimeric aldehydes. These results are explained on the basis of the involvement of discrete carbonium ion intermediates in the rearrangement processes.