Factors governing selectivity in removal of protecting groups

Factors Governing Selectivity in Removal of Protecting Groups [Pg.382]

The rate of hydrolysis of carbonyl protecting groups is often inversely proportional to their rate of formation. Thus the 7,17-bisketal (27) is cleaved [Pg.382]

The hydrolysis of dehydrocholic acid trishemithioketal (29) can be performed selectively to yield the 7,12-bishemithioketal (30), the 12-monohemi-thioketal (31) or the free triketone (32). [Pg.383]

Selective removal of the C-20 protecting group of the bisketal (33) is effected by using boron trifluoride to produce the 3-monoketal (34). [Pg.383]

The presence of neighboring substituents may strongly affect the stability of the protecting group, thus reversing the usual order of cleavage. [Pg.383]

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