Thermal rearrangement of N-arylmethyl- and N-alkyl-2,2-dihalogenocyclopropyl imines

Abstract

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.