Michael Addition−Elimination Mechanism for Nucleophilic Substitution Reaction of Cycloalkenyl Iodonium Salts and Selectivity of 1,2-Hydrogen Shift in Cycloalkylidene Intermediate
of allylic and vinylic forms. Deuterium-labeling experiments show that the allylic product is formed via the Michael addition of cyanide to the vinylic iodonium salt, followed by elimination of the iodonio group and 1,2-hydrogen shift in the 2-cyanocycloalkylidene intermediate. The hydrogen shift preferentially occurs from the methylene rather than the methine β-position of the carbene, and the selectivity