Abstract
Arene dearomatization reactions are an important class of synthetic technologies for the rapid assembly of unique chemical architectures. Herein, we report a catalytic protocol to initiate a carboamination/dearomatization cascade that proceeds through transient sulfonamidyl radical intermediates formed from native sulfonamide N–H bonds leading to 1,4-cyclohexadiene-fused sultams. Importantly, this work demonstrates a facile approach to employ two-dimensional aromatic compounds as modular building blocks to generate richly substituted, three-dimensional compounds. These reactions occur at room temperature under visible light irradiation and are catalyzed by the combination of an iridium(III) photocatalyst and a dialkyl phosphate base. Reaction optimization, substrate scope, mechanistic features, and synthetic applications of this transformation are presented.
Highlights
Arene dearomatization reactions are an important class of synthetic technologies for the rapid assembly of unique chemical architectures
A complementary strategy addressing the inherent drawbacks of the classic Birch reduction is to promote an arene dearomatization via a radical cascade sequence
With respect to sulfonamide-based N-radical alkene carboamination platforms, Kinoshita and co-workers[38] demonstrated that N-phenylbenzenesulfonamidyl radicals derived from homolysis of a symmetrical sulfonylhydrazide could add to alkenes to give mixtures of products, including sultams
Summary
Arene dearomatization reactions are an important class of synthetic technologies for the rapid assembly of unique chemical architectures. This work demonstrates a facile approach to employ two-dimensional aromatic compounds as modular building blocks to generate richly substituted, three-dimensional compounds These reactions occur at room temperature under visible light irradiation and are catalyzed by the combination of an iridium(III) photocatalyst and a dialkyl phosphate base. Modifications of the canonical Birch reduction conditions have expanded the scope and synthetic utility of the reaction[18,19,20,21,22] Both electrochemical[23] and visible light-mediated[24,25,26,27,28] arene dearomatization reactions have been reported with proven utility, they have not been integrated with other reaction pathways via reactive intermediates. The authors propose an excited-state redox catalyst and a weakly coordinating phosphate base, jointly mediate the concerted homolytic activation of the strong N–H bonds under visible light irradiation to afford transient N-centered amidyl and sulfonamidyl radicals capable of adding to olefins with anti-Markovnikov regioselectivity. Zhao et al.[44] have described a process for a radical 5-exo cyclization/addition/aromatization cascade of β,γ-unsaturated N-tosyl hydrazones under cooperative photocatalysis and cobalt catalysis enabling the synthesis of dihydropyrazole-fused benzosultams
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