A solution of 2.92 g of 3β,17β-diacetoxy-androst-5-en-18-al in 30 ml of tetrahydrofurane is added dropwise to a solution of a Wittig reagent prepared from 7.83 g of chloromethyl-triphenyl-phosphonium chloride, 144 ml of tetrahydrofurane, 2.23 ml of piperidine and 11.25 ml of a 1.56 molar solution of butyl-lithium in hexane and the mixture is allowed to react for 40 minutes at room temperature and is worked up as indicated in Example 1. On purification by chromatography, as also indicated in Example 1A, this gives the cis and trans isomers of 3β,17β-diacetoxy-13-(2-chlorovinyl)-10-methyl-gon-5-ene in a ratio of 1:3. The cis isomer crystallises from methylene chloride/hexane and then melts at 161°-162° C; [α]D25 = -70° (in chloroform); the trans isomer crystallises from methylene chloride/hexane, melting point 155°-156° C, [α]D25 = -42° (in chloroform).
