BF3.OEt2-catalyzed intermolecular reactions of vinylidenecyclopropanes with bis(p-alkoxyphenyl)methanols: a novel cationic 1,4-aryl-migration process.

BF(3)OEt(2)-catalyzed reactions of vinylidenecyclopropanes (VDCPs) 1 with bis(aryl)methanols 2 were thoroughly investigated. When VDCPs 1 reacted with electron-rich bis(aryl)methanols 2, diastereomeric rotamers of indene derivatives formed in excellent yields by a novel cationic 1,4-aryl migration between two carbon atoms and the subsequent intramolecular Friedel-Crafts reaction pathways in the presence of BF(3).OEt(2) under mild conditions. As for electron-deficient or less-electron-rich bis(aryl)methanols 2, either trialkene products formed in good yields by direct deprotonation, or another type of indene derivative was produced by direct intramolecular Friedel-Crafts reaction, depending on the substituents on the cyclopropane of VDCPs. In addition, DFT calculations were carried out to explain the experimental results. Plausible mechanisms for all these transformations are proposed on the basis of the experimental and computational results.