Ir-Catalyzed Selective B(3)-H Amination of o-Carboranes with NH3.

Ammonia gas, NH3, is a cheap and widely used industrial feedstock, which has received tremendous research interests in its functionalization. This work reports a breakthrough in catalytic selective cage B(3)-H amination of o-carboranes with NH3 via Ir-catalyzed B-H/N-H dehydrocoupling, offering convenient and efficient access to a series of 3-NH2-o-carborane derivatives in moderate to high isolated yields with a broad substrate scope. The employment of readily available NH3 gas as the aminating reagent with H2 as the sole byproduct endows the protocol economy, practicability, and environmental friendliness. A plausible reaction mechanism is proposed on the basis of control experiments.

Palladium-Catalyzed Carbonylative Annulation of 1-Hydroxy-o-Carborane and Internal Alkynes via Regioselective B-H Activation.

A Pd-catalyzed three-component carbonylative-annulation of 1-hydroxy-o-carborane, internal alkyne and carbon monoxide has been achieved via direct and regioselective cage B-H activation. A class of C,B-substituted carborano-coumarin derivatives with potential applications in pharmaceuticals were facilely prepared in moderate to high yields with excellent chemoselectivity and regioselectivity. A plausible reaction mechanism including CO insertion, electrophilic B-H metalation, alkyne insertion and reductive elimination was proposed.

Copper-Catalyzed Electrochemical Selective B-H Oxygenation of o-Carboranes at Room Temperature.

Copper-catalyzed electrochemical selective cage B-H oxygenation of o-carboranes has been achieved for the first time. Under a constant electric current (4.0 mA) at room temperature, copper-catalyzed cross-coupling of carboranyl amides with lithium phenolates results in the formation of B(4,5)-diphenolated o-carboranes via direct B-H activation, whereas the use of lithium tert-butoxide affords B(4)-monooxygenated products. This reaction does not require any additional chemical oxidants and generates H2 and a lithium salt as byproducts. Control experiments indicated that a high-valent Cu(III) species is likely involved in the reaction process.

Catalytic Cascade Dehydrogenative Cross-Coupling of BH/CH and BH/NH: One-Pot Process to Carborano-Isoquinolinone.

A proof-of-principle study of cascade dehydrogenative cross-coupling of carboranyl carboxylic acid with readily available benzamide has been achieved, resulting in the facile synthesis of previously inaccessible carborano-isoquinolinone derivatives in a simple one-pot process, in which two cage B-H, one aryl C-H, and one N-H bond were sequentially activated to construct efficiently new B-C and B-N bonds, respectively. Under suitable reaction conditions, such cascade cyclization can be stopped at the first B-H/C-H cross-coupling step to give a series of α-carboranyl benzamides, suggesting the preferential occurrence of B-C cross-coupling over that of B-N. The carboxylic acid directing group plays a key role in the B-C cross-coupling step, which is then removed through in situ decarboxylation. The CV results combined with control experiments indicate that high-valent Ir(V)-species may be involved in the reaction pathways, which is crucial for such cascade dehydrogenative cross-coupling reactions. The isolation and structural identification of a key intermediate, its controlled transformations, and deuterium labeling experiments support a new Ir-nitrene-mediated amination for B-H/N-H dehydrocoupling.