Heterocycles in organic synthesis. Part 19. Thermolysis of pyridinium N-acylimines : a new preparation of isocyanates

Abstract

2,4,6-Triphenylpyrylium perchlorate converts hydrazides into the 1-amidopyridinium perchlorates (25) which are easily deprotonated to the free pyridinium 1-acylimines (8). These are alternatively prepared by acylation of the 1-amino-2,4,6-triphenylpyridinium cation. The 1-acylimines undergo smooth thermolysis to 2,4,6-triphenylpyridine and the corresponding isocyanates, constituting a practical synthetic method for the latter. 1-Thioamidosalts (28) were prepared: the corresponding 1-thioacylimines are unstable and decompose to the corresponding cyanides and sulphur.