Construction of Naphtho[2,1-<i>d</i>]oxazoles and 1,4-Epoxyisoquinolines via Regioselectivity-Switchable Diels–Alder Reaction of 4-Alkenyloxazoles with Arynes

A Regioselectivity-switchable Diels-Alder reaction of arynes and 4-alkenyloxazoles was explored. By regulating the reaction temperature and the polarity of the solvent, the reaction activity of aryne was controlled to selectively react with different favorable reaction sites of 4-alkenyloxazoles, providing naphtho[2,1-<i>d</i>]oxazoles and 1,4-epoxyisoquinolines. Density functional theory (DFT) calculations demonstrated that the Diels-Alder reaction on acyclic dienes site needs more energy than the reaction on cyclic dienes to overcome the potential reaction barrier.