Intermolecular Hetero-Diels–Alder Reactions of Photogenerated aza-ortho-Quinone Methides with Aldehydes

A visible-light-driven, perfluoroalkyl radical-mediated strategy for in situ formation of aza-o-QMs from readily available precursors is reported. Combination of this method with a Brønsted base thus enables an efficient and highly diastereoselective HDA reaction between such photogenerated aza-o-QMs and π-electron-poor systems, aldehydes, providing high yielding and rapid access to valuable, diversely substituted dihydro­benzoxazines. DFT calculation elucidated the origins of stereochemistry of the products and disclosed the concerted property of the process.