Direct Nucleophilic Substitution Reaction of Cage B-H Bonds by Grignard Reagents: A Route to Regioselective B4-Alkylation of o-Carboranes.

Direct nucleophilic substitution reaction of cage B-H bonds of o-carboranes by Grignard reagents in the absence of any transition metals has been achieved for the first time, and leads to the regioselective synthesis of a series of 4-alkyl-1,2-diaryl-o-carboranes in very high yields. The presence of two electron-withdrawing aryl groups on the cage carbon atoms is crucial to realizing the reaction. The regioselectivity is controlled by both electronic and steric factors. This work represents a new strategy for the development of methods for carborane functionalization.