Reaction of cis-3-bromo-1,2-dibenzoylpropene with amines

The reaction of cis-3-bromo-1,2-dibenzoylpropene (1) with amines proceeds by means of a substitution-rearrangement attack to give the 2-(α-aminoacetophenonyl)acrylophenones ( 2 ). Like similar structures, 2 undergoes further substitution-rearrangement by amines to give 3-benzoyl-5-phenylpyrroles ( 5 ) and an enaminoketone, α-acetophenonyl-β-aminoacrylophenone ( 3 ). Competitive with substitution-rearrangement, amine addition to 2 followed by loss of hydrogen and then water leads to formation of the 3-benzoyl-4-amino-5-phenylpyrroles ( 4 ). The enaminoketones ( 3 ) by contrast with 2 are quite stable. Structure 2 when in polar solvents or in the presence of amines undergoes substitution-rearrangement to give 3 , which can be induced to give the pyrroles ( 5 ) when exposed to acid conditions. When neat or in solvents of low polarity, 2 undergoes intermolecular substitution-rearrangement-dehydration to give 5 almost exclusively. A novel addition reaction of 3-benzoyl-5-phenylfuran involving attack by isopropyl- or cyclohexylamine provides a quantitative method of synthesizing the appropriate N-substituted examples of 3 and an efficient method of deriving the corresponding pyrroles ( 5 ).