Nitropyridyl isocyanates in 1,3-dipolar cycloaddition reactions

The reactivity of 3-nitro-4-pyridyl isocyanate (7) and 5-nitropyridin-2-yl isocyanate (9) in 1,3-dipolar cycloaddition reactions with azides and pyridine N-oxides has been investigated. 1,3-Dipolar cycloaddition to trimethylsilylazide (TMSA) afforded the respective tetrazolinones, 1-(3-nitropyridin-4-yl)-1H-tetrazol-5(4H)one (8, 50%) and 1-(5-nitropyridin-2-yl)-1H-tetrazol-5(4H)one (11, 64%). Respectively, 1,3-dipolar cycloaddition of nitropyridyl isocyanates 7 and 9 to 3,5-dimethylpyridine N-oxide (14), 3-methylpyridine N-oxide (21) and pyridine N-oxide (22) gave the substituted amines, 3,5-dimethyl-N-(3-nitropyridin-4-yl)pyridin-2-amine (17), 3,5-dimethyl-N-(5-nitropyridin-2-yl)pyridin-2-amine (20), N-(5-nitropyridin-2-yl)pyridin-2-amine (24), 5-methyl-N-(5-nitropyridin-2-yl)pyridin-2-amine (23) and 3-methyl-N-(5-nitropyridin-2-yl)pyridin-2-amine (25) in 65-80% yield, obtained by cycloaddition, rearrangement and decarboxylation. The results demonstrate that the nitropyridyl isocyanates (7,9) readily undergo 1,3-dipolar cyloaddition reactions similar to phenyl isocyanates.