Sigmatropic Rearrangements Accompanying the Addition of Dichlorocarbene to Norbornadiene

A new product arising from the reaction of dichlorocarbene with norbornadiene, 6endo-(2,2-dichlorovinyl)-cis-bicyclo[3.1.0]hex-2-ene, is described. It does not arise from the normal exo-l,2-adduct, but possibly originates by sigmatropic rearrangement of an initially formed zwitterionic intermediate.