Carbene Reactivity of 4-Diazo-4<i>H</i>-imidazoles toward Nucleophiles and Aromatic Compounds

Carbenes derived from diazoimidazolecarboxylates <b>4</b> under thermal or photochemical conditions undergo O−H and N−H insertion reactions with alcohols and amines, respectively, in moderate yield, in competition with reduction in good H-donor solvents. Dichloromethane reacts to give the corresponding 4-chloroimidazole. Aromatic hydrocarbons are excellent traps for the imidazolylidene carbene and lead to a range of arylimidazole derivatives <b>7</b>. Reaction with pyridine leads to the first example of a pyridinium ylide <b>8</b> formed from an imidazolylidene carbene, whereas irradiation in hexafluorobenzene gives the imidazoazocine <b>11</b>, presumably by way of an initial norcaradiene intermediate.