Fe(II)-Catalyzed Isomerization of 4-Vinylisoxazoles into Pyrroles

摘要

The first synthesis of pyrroles by Fe(I)-catalyzed isomerization of 4-vinylisoxazoles is reported. 5-Alkoxy, amino, and N,N-dialkylamino-3-aryl/alkyl-4-(2-R-vinyl)isoxazoles afford 2-aryl/alky1-5-aryl/alkyl/methoxycarbonyl-1H-pyrrol-3-carboxylic acid derivatives typically under mild conditions with cheap and available FeCl2 center dot 4H(2)O as a catalyst. The isomerization of 5-alkoxy/amino-3-arylisoxazoles, bearing unsaturated carbo and heterocyclic substituents at the position 4, gives the corresponding fused pyrrolecarboxylic acid derivatives in high yields. DFT calculations were used to elucidate a probable mechanism of the isomerization and explain the influence of steric congestion of the vinyl moiety on the isomerization pathway.