Visible light-mediated syntheses of unsymmetrical methylene-bridged bis-heterocycles via an alkoxy radical relay reaction

Efficient and versatile syntheses of methylene-bridged bis-heterocycles that embody dihydroisoxazoline/pyridine or dihydroisoxazoline/quinoline pairings are described. These proceed under mild conditions and involve a visible light-mediated radical-relay sequence that begins with the homolysis of O-H bonds contained within & beta;,& gamma;-unsaturated oximes to generate oxygen-centred radicals that add to the tethered olefin. The ensuing carbon-centered radical is then trapped by an added N-heteroarenium salt. The results suggest that the radical-chain is sustained by hydrogen atom transfer between in situ generated methoxy radicals and oxime O-H bonds. Such outcomes provide new insights into alkoxy radical-mediated transformations promoted by visible light as well as access to new molecular scaffolds likely to be useful in a variety of settings.