Reactions in the B-Ring of Sterols

An alternate route to the 5,7-diene system is by the hydride induced decomposition of A 7-toluenesulfonylhydrazones (113) (31, 41). The corresponding 7-oxo-steroids (114) can be prepared by allylic oxidation of A -sterol esters with chromium trioxide-amine complexes in methylene chloride at room temperature (163). The attractive feature of this method is that the product formed in the toluenesulfonyl hydrazone decomposition is virtually free of the 4,6-diene isomer. 

The cholest-6-en-la,3P-diol (106) obtained in Mazxjr s liquid ammonia reduction of la,2a-epoxycholesta-4,6-dien-3-one has been brominated to give the corresponding 6,7-dibromide which was dehydro-halogenated in hexamethylphosphoramide containing triethyl methyl ammonium dimethylphosphate to give a mixture (1.3 1) of the 5,7-and 4,6-diene compounds (57). As mentioned above treatment of steroidal 

6- trien-3-ones with potassium butoxide in dimethylsulfoxide followed by quenching in mildly acidic water results in the formation of the unstable 

7- trien-3-one system (89). Immediate borohydride reduction serves to freeze the 5,7-diene in place and to give the corresponding 3P-ol derivative (95). 

Thermal equilibration of the previtamin (171) with the vitamin (2) occurs on brief warming of a solution in an oxygen-free atmosphere. This equilibration generally gives the vitamin as the major isomer but seldom is complete thus requiring chromatographic separation if pure vitamin is desired. 

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