A Procedure for the Facile Removal of Benzylidene Blocking Groups

Abstract

Often rather complex mixtures are formed in the alkylation of unsymmetrical ketones when the enolate ion population cannot be adequately controlled. One solution to this problem utilizes a prior base condensation to introduce a suitable blocking function. Benzylidene groups have been widely used for this purpose^1,2since they usually afford crystalline derivatives and their steric demands are greater than those for related procedures, permitting greater selectivity. A disadvantage, as House has pointed out³ is that “the arylidene blocking group is frequently difficult to remove after alkylation.” This difficulty has helped stimulate the development of various other blocking agents.⁴ Generally basic conditions alone are insufficient to remove the benzylidene function⁵ and the standard prooedure¹