Fragmentation of 16-oxygenated pregnanes

Treatment of 16a-mesyloxy or tosyloxy-20-hydroxypregnanes with base provides A -androstenes in ca. 30% yield 

The stereochemistry at C-20 does not affect the reaction. However, the 16j5-mesyloxy analogs give poor yields of fragmentation product, as would be predicted from the syn periplanar arrangement of the bonds involved. 

20a-Hydroxy-16-ketopregnanes on prolonged treatment with base undergo a reverse aldol reaction to give 16-ketoandrostanes in ca. 35-40% yield. Brief base treatment produces first the A °hi6 ketopregnane  

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