Synthesis of Pregn-17/20/-en-21-oic Acid Derivatives. The Wittig-Horner Reaction on Steroidal 17-Ketones

Abstract

In connection with the synthesis directed toward 25-hydroxycholesterol,^1/ and other cholestane derivatives hydroxylated in the side chain, the research was undertaken in order to find the most effective method for the preparation of pregn-17/20/-en-21-oic acid derivatives.^2/ In the present communication we would like to report the observation that contrary to the literature data, such pregnenoic acid derivatives can be conveniently obtained in very good yields by the Wittig-Horner reaction of 17-ketoandrostane derivatives and estrone with trialkyl phosphonoacetates when alcohols or DME are used as the reaction medium. In the previous reports the following statements have been made: 1/ the Wittig-Horner reaction of steroidal 17-ketones with trialkyl phosphonoacetates is compleetely inhibited as a result of the steric shielding of the carbonyl group^3a, 2/ this reaction gives very low yields^3b/, 3/ in the case of 17-ketoanderostane derivatives this reaction requires drastic conditions and is completely inhibited in the case of estrone/irrespective of conditions/^3c/.