A computational study of the chemistry of substituted 3-nitrenopyridine 1-oxides

The photolysis of 3-azidopyridine 1-oxide in argon matrices leads to an unusual product distribution that consists of the triplet nitrene, 1,4-diazacyclohepta-2,3,5,7-tetraene 1-oxide (obtained from ring expansion) and 2,7-diazabicyclo[4.1.0]hepta-2,4,6-triene 2-oxide (obtained from cyclization of the nitrene toward the N-oxide moiety). In order to investigate the possibility of utilizing judicious substitution of this system to selectively investigate the chemistry of the benzazirine system, a computational study of variously substituted 3-nitrenopyridine 1-oxides is described. The results indicate that the N-oxide plays a stabilizing role in these systems, but the kinetics and thermochemistry are still governed by an interplay of steric, polar and resonance effects; the importance of each determined by the nature of the substituents.