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-d ihalogenocyclopropyl imines is reported. The thermolysis of N-arylmeth yl-2,2-dichlorocyclopropanecarbaldimines 15a-h produces 2-aryl-16a-h a nd 2-aryl-4-chloro-pyridine derivatives 17a-h, while N-alkylcyclopropy l imines 15i, j yield N-alkylchloropyrroles. The 2,2-dibromocyclopropa ne analogue undergoes thermolysis at lower temperatures. An ionic mech anism triggered by the halide ion dissociation is proposed for the the rmal rearrangement on the basis of a study using deuteriated imine 15m , and the effects of additives and solvents. On the other hand, difluo rocyclopropyl 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.