An efficient Rh(III)- and Ir(III)-catalyzed, chelation-assisted C-H alkynylation of a broad scope of (hetero)arenes has been developed using hypervalent iodine-alkyne reagents. Heterocycles, N-methoxy imines, azomethine imines, secondary carboxamides, azo compounds, N-nitrosoamines, and nitrones are viable directing groups to entail ortho C-H alkynylation. The reaction proceeded under mild conditions and with controllable mono- and dialkynylation selectivity when both mono- and dialkynylation was observed. Rh(III) and Ir(III) catalysts exhibited complementary substrate scope in this reaction. The synthetic applications of the coupled products have been demonstrated in subsequent derivatization reactions. Some mechanistic studies have been conducted, and two Rh(III) complexes have been established as key reaction intermediates. The current C-H alkynylation system complements those previously reported under gold or palladium catalysis using hypervalent iodine reagents.

Fluorinated heterocycles play an important role in pharmaceutical and agrochemical industries. Herein, we report on the synthesis of four types of fluorinated heterocycles via rhodium(III)-catalyzed C-H activation of arenes/alkenes and versatile coupling with 2,2-difluorovinyl tosylate. With N-OMe benzamide being a directing group (DG), the reaction delivered a monofluorinated alkene with the retention of the tosylate functionality. Subsequent one-pot acid treatment allowed the efficient synthesis of 4-fluoroisoquinolin-1(2H)-ones and 5-fluoropyridin-2(1H)-ones. When N-OPiv benzamides were used, however, [4 + 2] cyclization occurred to provide gem-difluorinated dihydroisoquinolin-1(2H)-ones. Synthetic applications have been demonstrated and the ready availability of both the arene and the coupling partner highlighted the synthetic potentials of these protocols. Mechanistically, these two processes share a common process involving N-H deprotonation, C-H activation, and olefin insertion to form a 7-membered rhodacycle. Thereafter, different reaction pathways featuring β-F elimination and C-N bond formation are followed on the basis of density functional theory (DFT) studies. These two pathways are DG-dependent and led to the open chain and cyclization products, respectively. The mechanistic rationale was supported by detailed DFT studies. In particular, the origins of the intriguing selectivity in the competing β-F elimination versus C-N bond formation were elucidated. It was found that β-F elimination is a facile event and proceeds via a syn-coplanar transition state with a low energy barrier. The C-N bond formation proceeds via a facile migratory insertion of the Rh-C(alkyl) into the Rh(V) amido species. In both reactions, the migratory insertion of the alkene is turnover-limiting, which stays in good agreement with the experimental studies.

[Cp*Rh(III)]-catalyzed C-H activation of arenes assisted by an oxidizing N-O or N-N directing group has allowed the construction of a number of hetercycles. In contrast, a polar N-O bond is well-known to undergo O-atom transfer (OAT) to alkynes. Despite the liability of N-O bonds in both C-H activation and OAT, these two important areas evolved separately. In this report, [Cp*Rh(III)] catalysts integrate both areas in an efficient redox-neutral coupling of quinoline N-oxides with alkynes to afford α-(8-quinolyl)acetophenones. In this process the N-O bond acts as both a directing group for C-H activation and as an O-atom donor.