Lewis Acid Catalyzed Synthesis of Multisubstituted Pyrroles

Significance

Described is an efficient synthesis of polysubstituted pyrroles by a reaction of phenyliodonium ylides with enamine esters catalyzed by BF₃ diethyl etherate. The reaction was optimized in terms of solvent and the acidic catalyst, for example, triflic and trifluoroacetic acid both afforded good yields as well (in the range of 70%). The starting iodonium ylides are readily available from phenyliodoso diacetate and the corresponding dicarbonyl compounds. The substrate scope of both starting materials was well studied and the yields of products range from good to excellent. In the case of R^¹ = CH₂Cl, the overall yield was good but the reaction yielded, in addition to the chloropyrrole (R^¹ = CH₂Cl), to the corresponding hydroxy derivative (R^¹ = CH₂OH) in a ratio of 2:1.