Neighboring-Group Effects and Rearrangements in Reactions of Cyclopropylmethyl,Cyclobutyl, and Homoallyl Systems

The neighboring-group effect produced by a double bond in the homoallyl position or by a cyclopropane or cyclobutane ring leads to interesting rearrangements, which are discussed in this paper mainly from the point of view of mechanism, but also from that of preparative work. The question of the postulated non-classical carbonium ions acquires a special significance in this connection.