Preparation of selectively protected derivatives of 21-nor-5-pregnene-3β,20-diol

Abstract

The preparation of selectively protected derivatives of the title diol (III) is described. Derivatives with protected hydroxyl in position 3 (IV, V and VI) were obtained by p-toluenesulfonic acid-catalyzed reaction of etienic acid (I) with dihydropyran, ethyl vinyl ether and methyl vinyl ether, respectively, and subsequent hydride reduction. The protection of the free primary hydroxyl in these compounds and the subsequent removal of the acetal protecting group in position 3 represents a suitable approach to 20-protected derivatives. The relative rates of cleavage of the acetal protecting groups and reaction conditions are discussed.