Harnessing Electron Donor-Acceptor Complexes to Improve the Sustainability of the Enantioselective β-Alkylation of Aromatic Enals.

A novel and sustainable method is presented for the enantioselective β-alkylation of enals using an electron donor-acceptor (EDA) complex-based strategy. β-Alkyl-γ-azo aldehydes, important intermediates in the synthesis of bioactive compounds, are typically synthesized using organocatalysis, rhodium-catalyzed hydroformylations, or radical additions. Existing photoredox radical approaches-particularly those relying on iminium ion excitation-display severe limitations, particularly related to overall catalytic sustainability. In contrast, this approach uses long wavelenght visible light-induced single electron transfer within an EDA complex formed between an electron-rich silane and an electron-poor iminium ion, enabling radical formation under very mild conditions. This strategy eliminates the need for costly catalysts and inefficient light sources, significantly improving the sustainability of the process. A careful evaluation of the mass-based metrics quantitatively demonstrates that EDA complexes can be profitably exploited to enhance the overall sustainability of the chemical transformations. The proposed approach also expands the substrate scope to unprecedent products. Photophysical studies and mechanistic experiments support the proposed catalytic cycle, demonstrating the successful use of an EDA complex for the enantioselective radical β-alkylation of enals, and contributing to the development of more sustainable and environmentally friendly strategies in the synthesis of complex molecules.