Chirality probe approach to reactive intermediates - Primary vinyl cation and cycloalkyne

Molecular chirality of 4-methyleyclohexyhdenemethyl iodonium salt is used to probe the chirality of intermediate state of the reaction. A possible achiral intermediate, primary vinyl cation is excluded for the reactions of the iodonium salt under any reaction conditions employed, while achiral 5-methylcycloheptyne, formed via rearranged cation, is involved in the reaction with sulfonate. The reaction is extended to generation of some small ring cycloalkynes. Vinylic S(N)2 mechanisms are also proposed.