Cp*Ir(III) and Cp*Rh(III)-catalyzed annulation of salicylaldehydes with fluorinated vinyl tosylates

Theoretical Investigations on the Rh(III)-Catalyzed Oxidative C-H Activation/Annulation of Salicylaldehydes with Masked Enynes: Mechanism Insights and Regioselectivity Origins

The mechanism underlying the rhodium(III)-catalyzed reaction of the C-H alkenylation/annulation reaction of salicylaldehydes with enynes has been thoroughly investigated using DFT calculations. Based on mechanistic studies, our focus primarily lies on the regioselectivity of asymmetric alkynes inserting into the Rh-C bond and the involvement of the auxiliary group OAc- in these reactions. Our theoretical study uncovers that, with acetate assistance, a stepwise SN2' cyclization, 1,3-Rh migration, β-H elimination, and reductive elimination process occur. Furthermore, we also explore the role of substitution at Cα (CH3 vs H) in the reaction. As demonstrated in this work, these findings are applicable to other related reactions.

Rh(III)-catalyzed redox-neutral C-H alkenylation of benzamides with gem-difluorohomoallylic silyl ethers via β-H elimination

Fluorinated molecules are widely used in pharmaceutical and agrochemical industries. Herein we report the synthesis of 2-(3,3-difluoro-4-(silyloxy)but-1-en-1-yl)benzamides from the unprecedented rhodium(III)-catalyzed alkenylation of various benzamides with difluorohomoallylic silyl ethers. The practicability of this protocol is demonstrated by its broad substrate compatibility, good functional group tolerance, ready scalability and high regioselectivity. The oxygen in difluorohomoallylic silyl ethers makes β-H elimination feasible, which suppresses both the β-F elimination and dialkenylation of benzamides. This redox-neutral reaction proceeds efficiently via N-O bond cleavage without external oxidants and thus provides new opportunities for the synthesis of elaborate difluorinated compounds from readily available fluorinated synthons.

Cascade in Situ Iodination, Chromone Annulation, and Cyanation for Site-Selective Synthesis of 2-Cyanochromones

A facile cascade reaction for the site selective synthesis of 2-cyanochromones is described. By using simple o-hydroxyphenyl enaminones and potassium ferrocyanide trihydrate (K₄[Fe(CN)₆]₃·3H₂O) as starting materials and I₂/AlCl₃ as promoters, the products are furnished via tandem chromone ring formation and C-H cyanation. The in situ formation of 3-iodochromone and a formal 1,2-hydrogen atom transfer (HAT) process account for the unconventional site selectivity. In addition, the synthesis of 2-cyanoquinolin-4-one has been realized by employing corresponding 2-aminophenyl enaminone as substrate.

Rh(III)-Catalyzed Oxidative C-H Activation/Annulation of Salicylaldehydes with Masked Enynes for the Synthesis of Chromones

A rhodium(III)-catalyzed oxidative C-H activation/annulation of salicylaldehydes with propargylic acetates has been developed for the regioselective synthesis of 3-vinyl chromones in good yields with broad functional group tolerance. 3-Vinyl chromones were converted into biologically active benzo[c]xanthone by I₂-mediated oxidative electrocyclization.