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Lewis Acid Catalyzed Synthesis of Multisubstituted Pyrroles
J.-Y. Wang, X.-P. Wang, Z.-S. Yu, W. Yu*
Lanzhou University, P. R. of China
20 November 2009 (online)
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 R¹ = CH2Cl, the overall yield was good but the reaction yielded, in addition to the chloropyrrole (R¹ = CH2Cl), to the corresponding hydroxy derivative (R¹ = CH2OH) in a ratio of 2:1.