Acylarylnitrosamines. Part VI. Anomalous reactions with 2,5-di-methylfuran: the formation of 2-benzyl-5-methylfurans and 3-acetyl-1-aryl-4-arylazo-5-methylpyrazoles

Abstract

Novel reactions of acylarylnitrosamines [XC₆H₄·N(NO)·COR; R = Me, X = H, p-CO₂Et, p-MeO, m-CO₂Et, m-MeO, m-Me, or p-Me; R =p-ClC₆H₄, X = H] with 2,5-dimethylfuran in an excess of benzene at room temperature are reported. Interaction of the nitrosamine with the benzene component is minimal, the major products being 2-benzyl-5-methylfurans and/or 3-acetyl-1-aryl-4-arylazo-5-methylpyrazoles. It is tentatively suggested that a key step in the formation of the former is π-complexing of the diazonium cation with 2,5-dimethylfuran, the side chain protons of which then become sufficiently acidic to be removed by the acetate counter ion. In competition with this is azo-coupling at a vacant 3-position, followed by consecutive ring opening, further coupling, and cyclisation under the influence of the diazonium acetate ion pair. The reactions constitute further examples of the recently recognised high basicity of acetate ions in benzene solution.