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.