Nitropyridyl isocyanates in 1,3‐dipolar cycloaddition reactions

Abstract

Abstract magnified image 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)‐1 H ‐tetrazol‐5(4 H )one ( 8 , 50 %) and 1‐(5‐nitropyridin‐2‐yl)‐1 H ‐tetrazol‐5(4 H )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.