PHOTOCHEMICAL TRANSFORMATIONS OF DIENES: VII. STEREOCHEMISTRY OF ADDITION OF ALCOHOL, AND EFFECT OF SUBSTITUENTS AND ACIDS ON THE PHOTOCHEMISTRY OF CHOLESTA-3,5-DIENES
Results for the photolysis of 6-methylcholesta-3,5-diene are described. The photolysis of these and other dienes proceeds by a unimolecular process, giving bicyclobutanes, or a bimolecular process, giving carbonium ions. Reaction of the bicyclobutane with a protic solvent results in stereospecific incorporation of a proton (4β), whereas direct abstraction of a proton by a photo-excited species results in non-stereospecific abstraction. In the presence of small amounts of acid, more or in part new products, derived from the bimolecular pathway, are obtained.It was noted that the normal chromatographic elution sequence (alumina) of epimeric alcohols was reversed when thin-layer chromatography (silica gel) was used.