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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
Fe(II)-Catalyzed Isomerization of 4-Vinylisoxazoles into Pyrroles
Ekaterina E Galenko1, Vladimir A Bodunov1, Alexey V Galenko1
1Saint Petersburg State University , Institute of Chemistry, 7/9 Universitetskaya nab., St. Petersburg, 199034 Russia.
Abstract:
The first synthesis of pyrroles by Fe(II)-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/alkyl-5-aryl/alkyl/methoxycarbonyl-1H-pyrrol-3-carboxylic acid derivatives typically under mild conditions with cheap and available FeCl2·4H2O 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.
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