Halide Anion Activated Reactions of Michael Acceptors with Tropylium Ion

Tropylium bromide undergoes non-catalyzed, regioselective additions to a large variety of Michael acceptors. In this way, acrylic esters are converted into ß-bromo-α-cycloheptatrienyl-propionic esters. The reactions are interpreted by nucleophilic attack of bromide ions at the electron-deficient olefins and trapping of the incipient carbanion by the tropylium ion. Quantum chemical calculations were performed to elucidate the analogy to the amine or phosphine-catalyzed Rauhut-Currier reactions. Subsequent synthetic transformations of the bromo-cycloheptatrienylated adducts are reported.