Unusual reaction of allylic systems: homo- and cross-cyclizations leading to four-carbon rings

The reaction of stabilized allylic-type carbocations with electron rich olefins was investigated. In most cases a facile cyclobutane ring formation was observed by [2+2] cycloaddition reaction promoted by Brønsted or Lewis acids. Some attempts were made to investigate the mechanistic pathway. After de-racemization the chiral cyclobutane containing diols were obtained as a potential chiral platform for new ligands.