Matrix Isolation of o‐Quinoid Compounds – 6‐Imino‐2,4‐cyclohexadien‐1‐one and 1,2‐Diimino‐3,5‐cyclohexadiene

Abstract

Abstract6‐Imino‐2,4‐cyclohexadien‐1‐one (1b) and 1,2‐diimino‐3,5‐cyclohexadiene (1c) 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.