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.