Kinetic studies on the reaction of chlorosulfonyl isocyanate with monofluoroalkenes: experimental evidence for both stepwise and concerted mechanisms and a pre-equilibrium complex on the reaction pathway.

Chlorosulfonyl isocyanate (CSI) is reported to react with hydrocarbon alkenes by a stepwise dipolar pathway to give N-chlorosulfonyl-β-lactams that are readily reduced to β-lactams. Substitution of a vinyl hydrogen for a vinyl fluorine changes the dynamics for reaction with CSI so that a concerted pathway is favored. Rate constants were measured for reactions of CSI with monofluoroalkenes and some hydrocarbon alkenes.

Reaction of chlorosulfonyl isocyanate with fluorosubstituted alkenes: evidence of a concerted pathway.

Concerted reactions are indicated for the electrophilic addition of chlorosulfonyl isocyanate with monofluoroalkenes. A vinyl fluorine atom on an alkene raises the energy of a stepwise transition state more than the energy of the competing concerted pathway. This energy shift induces CSI to react with monofluoroalkenes by a one-step process.