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Fuks, Elina; Huber, Laura; Schinkel, Thea; Trapp, Oliver (2020): Investigation of Straightforward, Photoinduced Alkylations of Electron‐Rich Heterocompounds with Electron‐Deficient Alkyl Bromides in the Sole Presence of 2,6‐Lutidine. In: European Journal of Organic Chemistry, Vol. 2020, No. 39: pp. 6192-6198
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Abstract

Alkylations of simple electron‐rich heterocompounds deliver valuable target structures in bioorganic and medicinal chemistry. Herein, we present a straightforward and photosensitizer free approach for the photoinduced C–C coupling of electron‐rich unsaturated heterocompounds with alkyl bromides using 405 nm and 365 nm irradiation. Comprehensive mechanistic studies indicate the involvement of 2,6‐lutidine in the formation of a non‐covalently bound intermediate to which the function of a photosensitizer is attributed. UV/Vis spectra reveal the formation of a bathochromic shifted band when the electron‐deficient alkyl bromide is mixed with the structural motif of 2,6‐substituted pyridine. Upon photochemical excitation of this band, we find the initiation of the C–C bond‐forming reaction. Using this approach highly versatile alkylation products, e.g. α‐substituted ketones and 2‐substituted furan, thiophene, and pyrrole derivatives, are obtained in high selectivity. Furthermore, this synthetic methodology can be applied to access substituted indoles, which cannot be obtained by other transformations.