Accessing Polysubstituted NH Pyrroles from Nitroalkenes via [4+2]‐Cycloaddition/Reductive Ring Contraction Strategy

Abstract

A novel two‐step access to polysubstituted pyrroles from nitroalkenes was developed. It involves [4+2]‐cycloaddition with enol ethers to give six‐membered cyclic nitronates followed by reductive ring contraction with Ra‐Ni/AcOH or Ra‐Ni/EtOH systems. The process is applicable to a variety of nitroalkenes and enol ethers bearing electron‐rich and electron‐poor substituents and functional groups. The anti‐inflammatory drug Bimetopyrol and its structural modifications were successfully synthesized by the strategy developed. The key side products were identified that provided an insight into the mechanism of the developed reductive ring contraction to pyrroles.