Synthesis and spectroscopic studies of some substituted 3-benzoylpyrroles and their tricarbonylchromium complexes

Abstract

3-Benzoylpyrroles with a substituent on the pyrrole ring have been synthesized. Both the iodination and chlorination gave only the 2,4 derivatives while isopropylation gave mixtures of the 2,4 and 2,3 compounds. No 3,4 compounds were obtained. Both steric and electronic effects seem to determine the substitution pattern. The Cr(CO)3 complexes (Cr on the benzene ring) were prepared and these complexes, together with the uncomplexed pyrroles, were studied by IR, 1H-NMR, and ESR of the radical anions from the N-methylpyrrole derivatives. For the 2,4 compounds, the substituent on the pyrrole ring has relatively little effect on the spectral parameters of the benzene ring indicating relatively little electron delocalization between the two rings. 3-Benzoyl-2-isopropylpyrrole, however, gives an ESR spectrum very different from the other compounds. Keywords: benzoylpyrroles, tricarbonylchromium, ESR, chlorination, isopropylpyrroles.