Detailed study of oxidative esterification and elimination reactions undergone by a steroidal 17...

The reaction of 17 alpha-benzoyloxy-11 beta-hydroxy-3,20-dioxo-1, 4-pregnadien-21-al as the hemiacetal (1) with methanol:acetic acid:potassium cyanide:manganese dioxide followed by acetylation and preparative HPLC of the reaction mixture afforded 11 crystalline products. These products can be conveniently divided into three categories representing side-chain cleavage and oxidative esterification with or without elimination of the benzoyloxy group. Of special interest was the stereospecific formation of the C-17 cyanohydrin acetate 4a and the cis delta 17(20) enol acetate methyl ester 5. On the other hand, nonstereospecific addition of HCN to the side chain gave the C-20 epimeric cyanohydrin acetates 7a and 7b. The use of activated versus nonactivated MnO2 plays a major role in determining the quantitative distribution of the products. It was also discovered that even in the absence of MnO2, the reaction goes to completion. A proposed mechanism which explains the formation of all products is presented.