Selective B(5,8,9)-Triarylation Reaction of o-Carboranes through Determination of the Order of Introduction of Aryl Groups into B(4)-Acylamino-o-carboranes.

Palladium-catalyzed iterative cage B-H arylation reaction of a wide range of B(4)-acylamino-o-carboranes with aryl iodides has been developed, leading to the formation of B(5,8,9)-triarylated B(4)-acylamino-o-carboranes with excellent regioselectivity. Moreover, B(5,8,9)-triarylated carboranes bearing three different aryl groups were synthesized from B(4)-acylamino-o-carborane and three different aryl iodides. The order of introduction [B(9) > B(8) > B(5)] of aryl groups into the B(5,8,9)-triarylation reaction was determined for the first time through NMR monitoring and X-ray analyses.