Pyrolysis of Aryl Azides. XII. Mechanistic Implications of the Very Small Neighboring Group Effects Across the 2,3-Bond of 2-Azidonaphthalene

Abstract

2-Azidonaphthalenes with nitro, acetyl, benzoyl and methoxycarbonyl substituents in the 3-position have been synthesized and then pyrolysed in nitrobenzene solution. At 120°, the rates (relative to 2-azidonaphthalene) are respectively 27.9, 24.8, 5.00 and 3.67. These very small neighbouring group effects are consistent with a transition state which has considerable quinonoid character. No evidence of cyclic products was obtained from the two azides with nitro and ester neighbouring groups. With the two azido ketones there was infrared spectroscopic evidence of clean cyclization in dilute solution, to form the corresponding naphth [2,3-c] isoxazole. Our attempts to isolate these two naphthisoxazoles led to decomposition, though 3-methylnaphth[2,3-c] isoxazole has been reported previously ( Friedrichsen and Kaschner 1977).