Metal-Free Synthesis of Pyrroles From Morita-Baylis-Hillman Acetates

Significance

Reported is the synthesis of di­substituted pyrroles 3 by the reaction of Morita-Baylis-Hillman acetates 1 with amines 2 via a ­metal-free tandem allylic substitution-cycloiso­merization approach. Both aliphatic and aromatic amines participate efficiently in the reaction. Primary sulfonamides may also be used, allowing ­access to N-unsubstituted pyrroles by desulfo­nylation. In terms of the Morita-Baylis-Hillman coupling partner, alkyl and aromatic R^¹ substitution is tolerated, as is R^¹ = H. Fused pyrroles 4 and 5 were also prepared by the same method. Limited mechanistic studies suggest that the initial allylic substitution must give the E-isomer for the cycloisomerization to proceed.