Three‐Component Reactions of Isochromenylium Tetrafluoroborates via Non‐Classical [4+2]‐Intermediates: Mild One‐Step Metal‐Free Synthesis of Functionalized Dihydronaphthalenes and Tetrahydronaphthalenes

Two novel types of elegant three-component reactions of stable isochromenylium tetrafluoroborates (ICTBs) have been developed under mild metal-free conditions in this work. Mechanistically, these reactions are commonly initiated by a [4+2]-cycloaddition between the non-classical isochromenylium diene and the aldehyde-enol, and terminated by the following addition of weak nucleophiles, including nitriles or the second equivalent of aldehydes, in a one-pot fashion. The developed methodologies exhibit excellent chemoselectivity, regioselectivity, and diastereoselectivity, and provide a new convenient access to functionalized dihydronaphthalenes and tetrahydronaphthalenes.