Abstract
A unique C(sp3)–H/C(sp3)–H dehydrocoupling of N-benzylimines with saturated heterocycles is described. Using super electron donor (SED) 2-azaallyl anions and aryl iodides as electron acceptors, single-electron-transfer (SET) generates an aryl radical. Hydrogen atom transfer (HAT) from saturated heterocycles or toluenes to the aryl radical generates alkyl radicals or benzylic radicals, respectively. The newly formed alkyl radicals and benzylic radicals couple with the 2-azaallyl radicals with formation of new C–C bonds. Experimental evidence supports the key hydrogen-abstraction by the aryl radical, which determines the chemoselectivity of the radical–radical coupling reaction. It is noteworthy that this procedure avoids the use of traditional strong oxidants and transition metals.
Highlights
Cyclic ethers and amines are fundamental structural motifs in nature and are found in a vast number of bioactive compounds, small-molecule drugs[1] and functional materials
Despite signi cant progress in the synthesis of saturated heterocycles, approaches to their C–H activation and subsequent C–C bond formation remain in great demand
Scheme 2 Application of 2-azaallyl anions in radical coupling reactions. (a) Radical coupling strategies enabled by 2-azaallyl anions as super-electron-donors. (b) Tandem reactions for the synthesis of heterocycles. (c) Radical relay design for the synthesis of heterocyclic amine derivatives
Summary
Cyclic ethers and amines are fundamental structural motifs in nature and are found in a vast number of bioactive compounds, small-molecule drugs[1] and functional materials. Other strategies to activate the C(sp3)–H bonds of heterocycles include application of hydrogen atom transfer (HAT).[9] For example, Porta et al developed a radical coupling where HAT of aryl radical from THF was the key step for radical generation. Benzyl benzophenone imines.[15] We identi ed the inherent reducing nature of the highly colored 2-azaallyl anions, which enabled the introduction of a series of transition metal free coupling reactions (Scheme 2a).
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