Ketones, Aldehydes, and Carboxylic Acid Derivatives of Pyrrole

Abstract

A. Resonance Interaction between the Pyrrole Ring and the Carbonyl SubstituentThe low reactivity, compared with other aromatic aldehydes and ketones, of a-acylpyrroles with nucleophiles (see Section B) was originally explained as being due to the preferential existence of the acylpyrrole (Al) in the alternative tautomeric form (A2). (1) It has also been suggested that 2-formylpyrrole could be better formulated as the dimer (A3), (2) whilst other rationales for the abnormal behaviour of acylpyrroles were based upon the high stability of intermediate chelates (3) or of the pyrryl anions produced during the reactions with nucleophiles. (4) It is now evident from spectroscopic data