A novel dehydrative ring-transformation of 1-alkyl-3-aroylpyrrolidines into 1-alkyl-2-aryl-3-methylpyrroles

Article abstract of DOI:10.1246/bcsj.68.1969

When heated in an alcoholic solvent, such as ethylene glycol or butanol, 4-substituted 3-aroyl-1-alkylpyrrolidines, which are readily accessible via the condensation of an amino acid, paraformaldehyde, and 3-substituted 1-ary-2-propen-1-one, afforded 4-substituted 1-alkyl-2-aryl-3-methylpyrrole derivatives in good yields. The ring-transformation of 3,4-dibenzoyl-1-methyl-2-phenylpyrrolidine occurred in two directions, giving the corresponding 3-benzyl- and 3-methylpyrrole derivative. Also, bicyclic pyrroles, such as 1H,3H-pyrrolo[1,2-c]thiazole, 2,3-dihydro-1H-pyrrolizine, and 5,6,7,8-tetrahydroindolizine, were prepared by the ring-transformation of bicyclic aroylpyrrolidines obtained from the corresponding cyclic amino acids. A mechanism for the ring-transformation is proposed.