49. Radical Redox Annulations: A General Light-Driven Method for the Synthesis of Saturated Heterocycles
Philip R. D. Murray, Isabelle Nathalie-Marie Leibler, Sandrine M. Hell, Eris Villalona, Abigail G. Doyle, Robert R. Knowles
ACS Catal. 2022, 12, 13732–13740. DOI: 10.1021/acscatal.2c04316
ABSTRACT: We introduce here a two-component annulation strategy that provides access to a diverse collection of five- and six-membered saturated heterocycles from aryl alkenes and a family of redox-active radical precursors bearing tethered nucleophiles. This transformation is mediated by a combination of an Ir(III) photocatalyst and a Brønsted acid under visible-light irradiation. A reductive proton-coupled electron transfer generates a reactive radical which undergoes addition to an alkene. Then, an oxidative radical-polar crossover step leading to carbocation formation is followed by ring closure through cyclization of the tethered nucleophile. A wide range of heterocycles are easily accessible, including pyrrolidines, piperidines, tetrahydrofurans, morpholines, δ-valerolactones, and dioxanones. We demonstrate the scope of this approach through broad structural variation of both reaction components. This method is amenable to gram-scale preparation and to complex fragment coupling.