Cyclic (Alkyl)(amino)carbene Ligand-Promoted Nitro Deoxygenative Hydroboration with Chromium Catalysis: Scope, Mechanism, and Applications.

Transition metal catalysis that utilizes N-heterocyclic carbenes as noninnocent ligands in promoting transformations has not been well studied. We report here a cyclic (alkyl)(amino)carbene (CAAC) ligand-promoted nitro deoxygenative hydroboration with cost-effective chromium catalysis. Using 1 mol % of CAAC-Cr precatalyst, the addition of HBpin to nitro scaffolds leads to deoxygenation, allowing for the retention of various reducible functionalities and the compatibility of sensitive groups toward hydroboration, thereby providing a mild, chemoselective, and facile strategy to form anilines, as well as heteroaryl and aliphatic amine derivatives, with broad scope and particularly high turnover numbers (up to 1.8 × 106). Mechanistic studies, based on theoretical calculations, indicate that the CAAC ligand plays an important role in promoting polarity reversal of hydride of HBpin; it serves as an H-shuttle to facilitate deoxygenative hydroboration. The preparation of several commercially available pharmaceuticals by means of this strategy highlights its potential application in medicinal chemistry.

Iridium-Catalyzed, Weakly Coordination-Assisted Ortho-Alkynylation of (Hetero)aromatic Carboxylic Acids without Cyclization.

It is reported a weakly coordination-assisted alkynylation of aryl and heteroaryl carboxylic acids with iridium catalysis. The reaction is catalyzed by [{Cp*IrCl2}2] complex without cyclization, forming ortho-alkynylated aryl and heteroaryl carboxylic acids, and features high functional group tolerance and broad substrate scope under an air atmosphere. 2-(Hetero)aryl-substituted acetic acids were amenable to the alkynylation by forming an unusual six-membered ring cycloiridiated intermediate.