Asymmetric Palladium Migration for Synthesis of Chiral-at-Cage o-Carboranes.

Metal migration strategy can offer BH functionalization of o-carboranes at different positions from where initial bond activation occurs to achieve bifunctionalized o-carboranes in one reaction. We report in this article an enantioselective 3,4-bifunctionalization of o-carboranes via asymmetric Pd migration with a high efficiency and up to 98 % ee. This asymmetric catalysis has a broad substrates scope, leading to the preparation of a class of chiral-at-cage o-carborane derivatives.

Pd-catalyzed selective tetrafunctionalization of diiodo--carboranes.

A palladium-catalyzed highly selective tetrafunctionalization of 3,6-I2-o-carborane and 4,7-I2-o-carborane has been developed, leading to the preparation of 3,6-dialkenyl-4,11-R2-o-carboranes and 4,7-dialkenyl-5,11-R2-o-carboranes (R = alkyl, allyl and aryl) in moderate to excellent yields. This represents a new strategy for selective synthesis of polyfunctionalized o-carborane derivatives via a one-pot process.

Pd-Catalyzed sequential B(3)-I/B(4)-H bond activation for the synthesis of 3,4-benzo--carboranes.

A palladium-catalyzed sequential B(3)-I and B(4)-H bond activation has been achieved for the synthesis of 3,4-benzo-o-carboranes via a formal [2 + 2 + 2] cycloaddition of 3-I-o-carborane with 2 equiv. of arylalkynes. This represents a new protocol to construct o-carborane-fused cyclics in one process, in which the Pd fragment migrates formally from the B(3) to B(4) position of the cage.

Pd-Catalyzed Selective Bifunctionalization of 3-Iodo-o-Carborane by Pd Migration.

A palladium-catalyzed highly selective 3,4-bifunctionalization of 3-I-o-carborane has been developed, leading to the preparation of 3-alkenyl-4-R-o-carboranes (R=alkyl, alkynyl, aryl, allyl, CN, and amido) in high to excellent yields. This protocol combines the sequential activation of cage B(3)-I and B(4)-H bonds by Pd migration from exo-alkenyl sp C to cage B(4), which is driven by thermodynamic force. This represents a brand-new strategy for selective bifunctionalization of carboranes with two different substituents.