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Two improved syntheses of a potent human 5a-reductase inhibitor, epristeride, SK&F 105657, are described. The first synthesis starts from methyl 3-oxoandrost-4-ene-17/S-carboxylate (1), which is converted to epristeride (5) in four synthetic steps in 44% overall yield. The second synthesis starts from commercially available 3-oxoandrost-4-en-17/3-carboxylic acid ( 7), which is converted to epristeride (5) in two synthetic steps in 63% overall yield. Both syntheses are suitable for large scale production and have been employed to produce kilograms supplies of epristeride in high purity.

2,3-Dibromo-3-phenylpropiophenones eliminated both bromine and hydrogen bromide on reaction with dimethyloxosulphonium methylide (DMOSM) ; the resulting ap-unsaturated ketones formed cyclopropyl ketones which, when suitably substituted, continued to react with DMOSM, forming a variety of heterocyclic products. A contiguous cyclopropyl epoxide underwent ring-opening oxymercuriation with mercuric acetate via 5-oxypent-2-en-1 -01s. A cyclopropylcyclopropane analogue of the epoxide was stable at 300 "C.

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