On the Structure of Carbamoylated 2-Phenylaminopyridines

Unambiguous preparations of 2‐(N‐alkoxycarbonyl‐N‐phenyl)aminopyridine 1‐oxides are used to prove that the product from 2‐phenylaminopyridine 3 and phenyl isocyanate is the expected urea 2a. Recently a 1,2‐dihydropyridine derivative 1 [4] has been claimed to be the product from 3 and phenyl isocyanate. The exocyclic nitrogen of 3 invariably reacts as the nucleophile towards electrophiles such as carbonyl chloride, esters of chloromethanoic acid and aryl isocyanates. 1H n.m.r. and 13C n.m.r. spectra support the assigned structures of the products from these ractions.