THERMAL REARRANGEMENT OF YL-(2,2-DIHALO-1-PHENYLCYCLOPROPYL)METHYLENEAMINE, RYL-(2,2-DIHALO-1-PHENYLCYCLOPROPYL)METHYLENEAMINE TO 1-ALKYL-HALO-4-PHENYLPYRROLE, AND 1-ARYL-2-HALO-4-PHENYLPYRROLE 1-ARYL-3-HALO-4-PHENYLPYRROLE

The thermolysis of N-t-alkyl-, and N-aryl-(2,2-dichlorocyclopropyl)met hyleneamines yielded directly 1-t-alkyl, and 1-aryl-3-chloropyrroles a s the major products along with a slight amount of the 2-chloro isomer s. The transformation to the 3-chloropyrroles was enhanced in polar so lvents. But basic additives directed the thermal rearrangement into th e 1,2-bond cleavage of the cyclopropane ring, leading to the 2-chlorop yrroles. 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 u nique preparative tool for 2-, and 3-halo-4-phenylpyrrole derivatives.