Metal-free aryl cross-coupling directed by traceless linkers.

Haensch VG, Neuwirth T, Steinmetzer J, Kloss F, Beckert R, Gräfe S, Kupfer S, Hertweck C (2019) Metal-free aryl cross-coupling directed by traceless linkers. Chem Eur J 25(70), 16068-16073. PubMed Open Access PDF

Abstract

The metal-free, highly selective synthesis of biaryls poses a major challenge in organic synthesis. We report the scope and mechanism of a promising new approach to (hetero)biaryls by the photochemical fusion of aryl substituents tethered to a traceless sulfonamide linker (photosplicing). Interrogating photosplicing with varying reaction conditions and comparison of diverse synthetic probes (40 examples, including a suite of heterocycles) showed that the reaction has a surprisingly broad scope and involves neither metals nor radicals. Quantum chemical calculations revealed that the C-C bond is formed by an intramolecular photochemical process that involves an excited singlet state and the traverse of a five-membered transition state, thus warranting consistent ipso ipso coupling fidelity. These results demonstrate that photosplicing is a unique aryl cross-coupling method in the excited state that can be applied to synthesize a broad range of biaryls.

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doi: 10.1002/chem.201903582 PMID: 31621964