CATALYSIS BY LEWIS-ACIDS AT HIGH-PRESSURE AS A METHOD OF INVOLVING HINDERED STEROID DIENOPHILES IN THE DIELS-ALDER REACTION

The joint action of Lewis acids and high pressure permits the Diels-Alder reaction to be conducted with high yields with greatly sterically hindered steroid dienophiles, which are virtually unreactive under normal conditions. The [2 + 4]-cycloadditions of dienes to DELTA16-20-, DELTA1-3-, DELTA1,4-3-, and DELTA4,6-3-ketones proceed stereospecifically with the formation of one stereoisomer for each cycloadduct. The reactions of the steroid dienes studied give mixtures of two monocycloadducts at both double bonds of the steroid, with predominance of the adduct at the sterically less-hindered double bond (DELTA1- and DELTA6-). The method developed is a new method of producing various modified steroids with possible hormonal or antihormonal activity.