The preparation and thermal fragmentation of 2-Acyl-5-azidofurans

Abstract

The reaction of the nitrofurans (1)-(4) with sodium azide in Me₂SO gave the thermally unstable azidofurans (5)-(8), which decompose to give nitrogen and the (Z)-dioxoalkenenitriles (32) and(15)-(17) respectively. The azides (6)-(8), the (Z)-nitriles (15)-(17) and their (E)-isomers (18)-(20)were characterized by spectroscopic techniques. The nitriles were also characterized by formation of Diels-Alder adducts and quinoxaline derivatives. The nitriles (17) and (20) gave the adducts(21a,b) with 2,3-dimethylbuta-1,3-diene, and the nitriles (16) and (19) gave the adducts (23), (24)and (25) (or (26)) with diene (22). The quinoxalines (27)-(31) were prepared by condensation of o-phenylenediamine with nitriles (17), (20), (18) and the unstable compounds (32) and (33) respectively. The first-order rate constants for ring-opening of azides (5)-(8) were determined by u.v. spectroscopy in cyclohexane and activation parameters were also evaluated. The trends in activation energies and entropies were rationalized by consideration of valence-bond contributors to the azides and the presumed nitrene intermediates. The acid-catalysed decomposition of azide (5) in methanol was also studied.