Lewis Acid-mediated Formation of 1,3-Disubstituted Spiro[cyclopropane-1,2'-indanes]: The Activating Effect of the Cyclopropane Walsh Orbital

By virtue of its alkylidenecyclopropane moiety 2-(cyclopropylidenemethyl)benzaldehyde reacts with a range of amines or thiols under Lewis acid catalysis yielding the respective 1,3-bis(arylamino) or -bis(arylthio and alkylthio)indanes spirolinked to the cyclopropane ring at carbon 2. The reaction mechanism and the peculiar contribution of the cyclopropane ring have been scrutinized by DFT calculations.