THERMAL REARRANGEMENT OF N-ARYLMETHYL-2,2-DIHALOGENOCYCLOPROPYL AND N-ALKYL-2,2-DIHALOGENOCYCLOPROPYL IMINES

An extended study of the thermal isomerization of 1 -substituted 2,2-dihalogenocyclopropyl imines is reported. The thermolysis of N-arylmethyl-2,2-dichlorocyclopropanecarbaldimines 15a-h produces 2-aryl-16a-h and 2-aryl-4-chloro-pyridine derivatives 17a-h, while N-alkylcyclopropyl imines 15i, j yield N-alkylchloropyrroles. The 2,2-dibromocyclopropane analogue undergoes thermolysis at lower temperatures. An ionic mechanism triggered by the halide ion dissociation is proposed for the thermal rearrangement on the basis of a study using deuteriated imine 15m, and the effects of additives and solvents. On the other hand, difluorocyclopropyl imine undergoes a homolytic cleavage of cyclopropane 1,3-bond with lower activation energy than the dichlorocyclopropyl imine, and afforded the N-alkyl-3-fluoropyrrole derivative preferentially.