Cobalt-Catalyzed Regioselective Ortho C(sp2)-H Bond Nitration of Aromatics through Proton-Coupled Electron Transfer Assistance.

A cobalt-catalyzed proton-coupled electron transfer (PCET) mediated regioselective ortho-specific nitration of aromatic C(sp2)-H bonds using chelation-assisted removable vicinal diamine directing groups was developed. The reaction proceeded under mild conditions in the presence of Co(OAc)2·4H2O as the catalyst with AgNO2 utilized as the nitro source as well as terminal oxidant in the presence of O2 as an external oxidant. No external base or additives were required for this process. Controlled experiments and mechanistic investigations with DFT calculations revealed that the reaction proceeds through a PCET promoted nitro functional group transfer pathway. Moreover, the produced compounds are valuable and pharmaceutically quite relevant.

Palladium/Silver Synergistic Catalysis in Direct Aerobic Carbonylation of C(sp(2))-H Bonds Using DMF as a Carbon Source: Synthesis of Pyrido-Fused Quinazolinones and Phenanthridinones.

An unprecedented Pd/Ag synergistic catalysis in the direct carbonylation of C(sp(2))-H bonds utilizing DMF as the carbon source under oxygen is described and demonstrated in the synthesis of pyrido-fused quinazolinone and phenanthridinone scaffolds. Control experiments indicated that the "C" of the carbonyl group is derived from the methyl group of DMF and "O" originates from oxygen as in the case of Ge's recent work. This transformation offers an alternative avenue for "CO-free" carbonylations.

Copper-Catalyzed Inter- and Intramolecular C-N Bond Formation: Synthesis of Benzimidazole-Fused Heterocycles.

A Cu (II)-catalyzed, inter/intramolecular C-N bond formation for the synthesis of various benzimidazole-fused heterocycles in a concise manner has been reported. The robustness of this reaction is demonstrated by the synthesis of a series of benzimidazole-fused heteroaromatics (e.g., pyrido[1,2-a] benzimidazole, benzimidazo[1,2-a]quinolines, benzimidazo [1,2-a]pyrazine, benzo[4,5] imidazo[2,1-b]thiazoles) directly from 2-aminoheteroarenens and 2-iodoarylboronic acids in one-pot. The novel cascade protocol for C-N bond formation operates via unique combination of Chan-Lam type coupling followed by Ullmann-type reaction.

Copper-catalyzed sequential N-arylation of C-amino-NH-azoles.

Copper(II)-catalyzed boronic acid promoted C-N bond cross-coupling reactions have been successfully developed for sequential N-arylation of C-amino-NH-azoles. These general protocols are compatible with a variety of aryl/hetero-aryl boronic acids and provided rapid access to a diverse array of diarylaminoazole derivatives in a two-step sequence or in one-pot.