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.

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A new type of chiral bicycle imidazole nucleophilic catalyst was rationally designed, facilely synthesized, and successfully applied in an asymmetric Steglich rearrangement with good to excellent yield and enantioselectivity at ambient temperature. Moreover, it can be easily recycled with almost no reduction of catalytic efficiency. This is the first example for the successful chiral imidazole nucleophilic catalyst without H-bonding assistance.

Getting a handle on it: In the chelation‐assisted title reactions in the presence of a hypervalent iodine oxidant, sodium azide and sodium nitrite served as readily available nitrogen sources, and pyridine, pyrimidine, and pyrazole substituents were efficient directing groups (DGs; see scheme; Cp*=C5Me5). The synthetic utility of the azidation products was demonstrated in subsequent functional‐group transformations.

Formal regiodivergent C-H alkynylation of 2-pyridones bearing different N-substituents has been realized under Au(I) and Rh(III) catalysis using a hypervalent iodine alkyne reagent. When catalyzed by Au(I), the alkynylation occurred at the most electron-rich 5-position via an electrophilic alkynylation pathway. The selectivity was switched to the 6-position under assistance of an N-chelation group when a Rh(III) catalyst was employed. A rhodacylic complex has been isolated as a key intermediate.

Functionalizable directing groups (DGs) are highly desirable in C-H activation chemistry. The nitrone DGs are explored in rhodium(III)-catalyzed C-H activation of arenes and couplings with cyclopropenones. N-tert-butyl nitrones bearing a small ortho substituent coupled to afford 1-naphthols, where the nitrone acts as a traceless DG. In contrast, coupling of N-tert-butyl nitrones bearing a bulky ortho group follows a C-H acylation/[3+2] dipolar addition pathway to give bicyclics. The coupling of N-arylnitrones follows the same acylation/[3+2] addition process but delivers different bicyclics.

C−H activation under redox-neutral conditions, especially by Rh(III) catalysis, has offered attractive synthetic strategies. Previous work in redox-neutral C−H activation relied heavily on the cleavage of oxidizing N−O and N−N directing groups, and cleavable N−S bonds have been rarely used, although they may offer complementary coupling patterns. In this work, N-sulfinyl ketoimines were designed as a novel substrate for the redox-neutral coupling with different activated olefins via a Rh-catalyzed C−H activation pathway. The coupling with acrylate esters afforded 1H-isoindoles with the formation of three chemical bonds around a quaternary carbon. Furthermore, the coupling with maleimides furnished pyrrolidone-fused isoquinolines. A broad scope of substrates has been established. The mechanism of the coupling with acrylates has been studied in detail by a combination of experimental and computational methods. This coupling proceeds via imine-assisted C−H activation of the arene followed by ortho C−H olefination to afford a Rh(III) olefin hydride intermediate which, upon deprotonation, may exist in equilibrium with a Rh(I) olefin species. Cleavage of the N−S bond occurs only after C−H olefination to generate a Rh(III) imide species. DFT studies indicated that the imide group can undergo migratory insertion to produce a Rh(III) secondary alkyl which isomerizes under the assistance of acetic acid to a Rh(III) tertiary alkyl that is prone to insertion of the second acrylate.