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Carbene Reactivity of 4-Diazo-4H-imidazoles toward Nucleophiles and Aromatic Compounds

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posted on 18.12.2009 by Matthew R. Smith, Alexander J. Blake, Christopher J. Hayes, Malcolm F. G. Stevens, Christopher J. Moody
Carbenes derived from diazoimidazolecarboxylates 4 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 7. Reaction with pyridine leads to the first example of a pyridinium ylide 8 formed from an imidazolylidene carbene, whereas irradiation in hexafluorobenzene gives the imidazoazocine 11, presumably by way of an initial norcaradiene intermediate.