Reaction of aromatic N-oxides with dipolarophiles. V. 1,3-Cycloaddition of 2-substituted pyridine N-oxides with phenyl isocyanates.

Abstract

The reaction of 2, 3-lutidine N-oxide (I) with phenyl isocyanate (IIa) in dimethyl-formamide at 110°C gave a 1 : 2 adduct (IIIa). Under reflux in ethanolic potassium hydroxide, IIIa readily lost a component of IIa and was converted to 5-methyl-6-N-phenylcarbamoylmethyl-3-pyridinol (IVa) in 95% yield. 2-Phenylpyridine N-oxides (V-VII) reacted with phenyl isocyanates (II) to afford 1 : 1 cycloadducts (IX-XI and XII-XIV). The reaction of 2-(p-nitrophenyl) pyridine N-oxide (VIII) with IIa directly afforded 2-anilino-6-(p-nitrophenyl) pyridine derivatives (XIVa and XVa).