Abstract
N-Arylation of NH-sulfoximines represents an appealing approach to access N-aryl sulfoximines, but has not been successfully applied to NH-diaryl sulfoximines. Herein, a copper-catalyzed photoredox dehydrogenative Chan-Lam coupling of free diaryl sulfoximines and arylboronic acids is described. This neutral and ligand-free coupling is initiated by ambient light-induced copper-catalyzed single-electron reduction of NH-sulfoximines. This electron transfer route circumvents the sacrificial oxidant employed in traditional Chan-Lam coupling reactions, increasing the environmental friendliness of this process. Instead, dihydrogen gas forms as a byproduct of this reaction. Mechanistic investigations also reveal a unique autocatalysis process. The C–N coupling products, N-arylated sulfoximines, serve as ligands along with NH-sulfoximine to bind to the copper species, generating the photocatalyst. DFT calculations reveal that both the NH-sulfoximine substrate and the N-aryl product can ligate the copper accounting for the observed autocatalysis. Two energetically viable stepwise pathways were located wherein the copper facilitates hydrogen atom abstraction from the NH-sulfoximine and the ethanol solvent to produce dihydrogen. The protocol described herein represents an appealing alternative strategy to the classic oxidative Chan-Lam reaction, allowing greater substrate generality as well as the elimination of byproduct formation from oxidants.
Highlights
N-Arylation of NH-sulfoximines represents an appealing approach to access N-aryl sulfoximines, but has not been successfully applied to NH-diaryl sulfoximines
General methods for the N-arylation of diaryl NH-sulfoximines, Ar2SO(NH), using the Buchwald–Hartwig approach have not been developed to date
The first systematic study of the arylation of diaryl NH-sulfoximines was disclosed by the Yu group (Fig. 1b)[21]
Summary
N-Arylation of NH-sulfoximines represents an appealing approach to access N-aryl sulfoximines, but has not been successfully applied to NH-diaryl sulfoximines. A coppercatalyzed photoredox dehydrogenative Chan-Lam coupling of free diaryl sulfoximines and arylboronic acids is described This neutral and ligand-free coupling is initiated by ambient light-induced copper-catalyzed single-electron reduction of NH-sulfoximines. General methods for the N-arylation of diaryl NH-sulfoximines, Ar2SO(NH), using the Buchwald–Hartwig approach have not been developed to date. The only successful examples of arylations of diaryl NH-sulfoximines [Ar2SO(NH)] employed diaryliodonium salts (two examples)[19] or aryl tosylates (three examples)[20] as coupling partners. These advances are of significance, the scope they define is quite narrow and currently unsuitable for generating diversity. A direct and efficient N-arylation protocol for NH-diaryl sulfoximines with broad substrate scope, including heteroaryl coupling partners, is still an unmet need
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