Rhodium-catalyzed sequential B(3)-, B(4)-, and B(5)-trifunctionalization of o -carboranes with three different substituents.

A rhodium-catalyzed one-pot trifunctionalization of o -carboranes with three different substituents via a carboxy group directed sequential B(5)-alkenylation, B(4)-alkyne annulation and B(3)-acyloxylation has been developed for the first time, leading to the synthesis of a new class of B(3,4,5)-trisubstituted o-carborane derivatives. Treatment of 1-COOH-2-CH 3 - o -C 2 B 10 H 10 with ArCCAr in the presence of a [Cp*RhCl 2 ] 2 catalyst and a Cu(OPiv) 2 oxidant gave 1,4-[COOC(Ar)C(Ar)]-2-Me-3-OPiv-5-[C(Ar)CH(Ar)- o -C 2 B 10 H 7 in good to high yields. This protocol represents a new strategy for the catalytic selective polyfunctionalization of carboranes with different substituents.