6-lmino-2,4-cyclohexadien-1-one (Ib) and 1,2-diimino-3,5-cyclohexadiene (Ic) were generated in high yields from o-azidophenol (5b) and o-azidoaniline (5c), respectively, by irradiation in argon matrices at 10 K or by flash vacuum pyrolysis (FVP) with subsequent trapping of the products in solid argon. The hydrogen shift in the phenylnitrenes 6 formed as primary intermediates is very rapid, and thus the nitrenes are short-lived transients even under the conditions of matrix isolation. Ring expansion to azacycloheptatetraenes was not observed. FVP produces the thermodynamically most stable E/Z isomers of the quinones as the main products. Photolysis of the matrix-isolated quinones results in photostationary equilibria of the E/Z isomers. The stereoisomers were identified by comparison of the matrix IR spectra with ab initio calculations at the RMP2-FC-6/31G(d) level of theory.
