Thermal Rearrangement of N-Alkyl-, and N-Aryl-(2,2-dihalo-1-phenylcyclopropyl)methyleneamines to 1-Alkyl-, and 1-Aryl-2 (or 3)-halo-4-phenylpyrroles

Abstract

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.

Syntheses ofgem-Dihalocyclopropanes and Their Use in Organic Synthesis

“…The thermolysis of N-tert-alkyl-and N-aryl-2,2dihalocyclopropanecarboxaldimines gives tert-alkylor aryl-substituted 3-halopyrroles, respectively (eq 103). 145 An ionic mechanism for chloropyrrole formation is proposed, while a homolytic pathway is proposed for fluoro derivatives. Basic additives (6 molar equivalents) lead to 2-chloropyrroles via a 1,2 bond cleavage of the cyclopropane ring.…”

“…The direction of the reaction of α,β-unsaturated nitriles with chloroform under PTC conditions depends on the structure of the nitrile and to some extent on the kind of catalyst. In the presence of TEBA, acrylonitrile 140 and its 3-substituted derivatives 140 exclusively gave Michael adducts, ( E )-2-phenyl-2-butenenitrile added dichlorocarbene, and methacrylonitrile formed a mixture of chain and cyclic products . When TMA was the catalyst, methacrylonitrile formed only the cyclopropane product in high yield (eq 28) …”

1,4-Disubstituted and 1,4,5-Trisubstituted 2-[(Benzotriazol-1-yl)methyl]pyrroles as Versatile Synthetic Intermediates

“…Novel syntheses of pyrroles are of current interest. − 2-(Functionalized-methyl)pyrroles 1 and 2-alkenylpyrroles 2 are versatile intermediates in organic synthesis, especially for natural products. ,− Owing to their great synthetic importance, a range of pyrrole intermediates containing 2-CH 2 X groups have been studied ,,− in which X has varied widely: halogen, hydroxy, alkoxy, alkylthio, amino, cyano, etc ., as shown in Chart . Among these, halogenomethyl groups have been most frequently employed inter alia for the preparation of other CH 2 X groups by nucleophilic substitutions. , However, the use of CH 2 -halogen groups is limited to the pyrroles in which all the ring carbons are substituted, otherwise difficulties arise from their instability and sensitivity to rapid intermolecular nucleophilic attack to form polymers. ,− Quaternary ammonium groups of type CH 2 N + R 3 can also be displaced by nucleophiles. , The other functional groups CH 2 X mentioned above are less susceptible to nucleophilic substitution.…”

Traceless Directing Group Enabled One‐Pot Regiospecific Synthesis of 2,3‐Diaryl‐4‐Fluoropyrroles

“…On the other hand, the utility of fluorinated building blocks to construct such demanding structures have been extensively studied. Previous work includes intramolecular cyclization, [6] ring expansion, [7] and intermolecular cycloaddition. [8] Among them, intermolecular [3 + 2] cycloaddition stands out with easy access of starting materials, high versatility and conciseness.…”