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 and thiols under Lewis acid catalysis. These reactions yield 1,3-bis(arylamino) and 1,3-bis(arylthio and alkylthio)indanes, respectively, which are spirolinked to the cyclopropane ring at carbon 2. The reaction mechanism, and the peculiar contribution of the cyclopropane ring, have been scrutinized via DFT calculations.