MATRIX-ISOLATION OF O-QUINOID COMPOUNDS - 6-IMINO-2,4-CYCLOHEXADIEN-1-ONE AND 1,2-DIIMINO-3,5-CYCLOHEXADIENE

6-lmino-2,4-cyclohexadien-1-one (Ib) and 1,2-diimino-3,5-cyclohexadien e (Ic) were generated in high yields from o-azidophenol (5b) and o-azi doaniline (5c), respectively, by irradiation in argon matrices at 10 K or by flash vacuum pyrolysis (FVP) with subsequent trapping of the pr oducts in solid argon. The hydrogen shift in the phenylnitrenes 6 form ed as primary intermediates is very rapid, and thus the nitrenes are s hort-lived transients even under the conditions of matrix isolation. R ing 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 p hotostationary equilibria of the E/Z isomers. The stereoisomers were i dentified by comparison of the matrix IR spectra with ab initio calcul ations at the RMP2-FC-6/31G(d) level of theory.