New synthesis of 2,2′-heteroarylpyrroles from heteroarylchlorocarbenes

2,2'-Pyridyl- and 2,2'-thienylpyrroles containing substituents at the 1- and 3-positions of the pyrrole ring have been prepared from the reaction of heteroarylchlorocarbenes with 1-azabuta-1,3-dienes. Laser flash photolysis of heteroarylchlorocarbene in isooctane in the presence of 1-azabuta-1,3-diene yields an azomethine ylide (lambda=550 nm) as an intermediate. The kinetic parameters for the ylide formation and further 1,5-intramolecular cyclization to the pyrrole ring have been determined. (C) 1999 Elsevier Science Ltd. All rights reserved.