Aluminum chloride catalyzed oligomerization of ketene imines and incorporation of carbon dioxide in an open-chain dimer

Aluminum trichloride and diethylaluminum chloride induce cyclodimerization and cyclotrimerization of three C,C-dimethylketene N-arylimines to quinazoline, azetidine, and triazine derivatives. The product distribution depends on the catalyst, the molar ratio of ketene imine to catalyst, and the substitution in the N-aryl group. On the other hand, C-methylketene N-mesitylimine forms an open-chain dimer, viz., an iminoketene imine which is detected by spectral means and trapped with methanol or carbon dioxide. X-ray crystallography of the latter adduct proves the l,3-oxazin-2-one structure. The reactions occur through open-chain intermediates deriving from the attack of nitrogen, or the terminal cumulative carbon of a ketene imine molecule, at the central carbon of another molecule which is coordinated to the Lewis acid.