THERMAL REARRANGEMENT OF N-ALKYL-(2,2-DIHALO-1-PHENYLCYCLOPROPYL)METHYLENEAMINE, N-ARYL-(2,2-DIHALO-1-PHENYLCYCLOPROPYL)METHYLENEAMINE TO 1-ALKYL-2-HALO-4-PHENYLPYRROLE OR 1-ALKYL-3-HALO-4-PHENYLPYRROLE, AND 1-ARY L-2-HALO-4-PHENYLPYRROLE OR 1-ARYL-3-HALO-4-PHENYLPYRROLE

The thermolysis of N-t-alkyl-, and N-aryl-(2,2-dichlorocyclopropyl)methyleneamines yielded directly 1-t-alkyl, and 1-aryl-3-chloropyrroles as the major products along with a slight amount of the 2-chloro isomers. The transformation to the 3-chloropyrroles was enhanced in polar solvents. But basic additives directed the thermal rearrangement into the 1,2-bond cleavage of the cyclopropane ring, leading to the 2-chloropyrroles. On the other hand, (difluorocyclopropyl)methyleneamines were pyrolyzed exclusively to 3-fluoropyrroles under 1,3-bond cleavage. The ionic mechanism involving a heterolytic dissociation of chlorine atom under 1,3-bond scission of the cyclopropane ring is proposed for the rearrangement to 3-chloropyrroles, while a homolytic cleavage pathway is proposed for 3-fluoropyrroles. The present thermolysis supplies a unique preparative tool for 2-, and 3-halo-4-phenylpyrrole derivatives.