Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The acid catalysed cleavage of 4,4-dimethyl-4a,5-epoxy-A-homocholestane derivatives bearing an oxygen-containing substituent (OH, OCOCH₃, OCH₃) in the position 3 with hydrobromic acid or aqueous perchloric acid was investigated. It was found that 4a,5-epoxides of 4,4-dimethyl-A-homocholestane series are opened on the side of the more substituted carbon atom C₍₅₎, where a normal cleavage leads to the formation of 4a-hydroxy-5,6-unsaturated derivatives, while the participation of the substituent in the position 3 leads to 3,5-epoxides. In none of the investigated epoxides was an attack of an external nucleophile observed. The effect of the nature of the substituent in the position 3 on the ratio of the products of a normal cleavage and the participation of the 3-substituent is discussed from the point of view of conformational effects. The dependence of the products ratio on the nucleophilicity of the acid used is also discussed.