Regio- and Diastereoselective Stepwise [8 + 3]-Cycloaddition Reaction between Tropone Derivatives and Donor–Acceptor Cyclopropanes

A novel SnCl4-catalyzed [8 + 3]-cycloaddition reaction between tropone derivatives and donor–acceptor aminocyclopropanes is described. The process leads to the formation of amino-substituted tetrahydrocyclohepta[b]pyrans with complete regio- and diastereoselectivity. Density functional theory calculations suggest that the cycloaddition occurs stepwise through an aromatic zwitterionic intermediate.