5a-Cholestan-3a-and

A recent study of the reduction of cholest-4-en-3-one with an excess of NaBH4 in 2-propanol shows that the corresponding cholest-4-en-3 -ol is the major product (44% yield) 4 other compounds (5a-cholestan-3a- and -3jS-ols, a sterol, possibly 5y -cholestan-3l -ol and an unidentified hydrocarbon) have also been isolated. When the reduction is carried out in the presence of ultraviolet light cholest-4-en-3/5-ol is still the major product (34%) but 7 other products are also obtained. These results show clearly the benefit of using Li[OC(CH3)3]3AlH for the preparation of the 4-en-3 -ol. ... 

Nucleo diiiic Substitution.—Further studies with unhindered secondary hydroxy-steroids confirm earlier reports of almost total inversion of configuration in reactions with PCls. However, thionyl chloride is less efficient than is generally believed in giving chloro-compounds with retention of configuration (SnI reaction). Thus 5a-cholestan-3a- and -3/5-ol with thionyl chloride each gave mixtures of... 

The study of sulfur-bridged carbocycles " has revealed a very interesting S-3 effect that is somewhat contradictory to the above conclusions and unprecedented in studies of ether groups (see Chapter 4). Results of a study of the rates of hydrolysis of the 2,5-epithio-5a-cholestan-3) -yl bromide endo (12)], the 3a-yl methanesulfonate exo (13)], the 3/S-bromide of the corresponding sulfoxide [endo (14)], and of the 2a,5-epoxy-5a-cholestan-3a- and 3)8-yl methanesulfonates [exo (15) and endo (15), re-... 

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