2-Oxo-substituted aryl azides such as 2-azidobenzenecarbaldehyde 1, 1-(2-azidophenyl)-1-
ethanone 2 and (2-azidophenyl) (phenyl)methanone 3 react with benzene in the presence of
BF3•OEt2, mainly affording 9-substituted acridines via formal 2-anilino-oxobenzene-BF3
complexes rapidly followed by intramolecular cyclo-dehydration at the activated carbonyl
groups. Under the same conditions, 2-azidobenzoic acid 4 gives mainly 2-anilinobenzoic acid 4b
together with trace amounts of the 9(10H)-acridinone 4a. On the other hand, 2-
azidobenzenecarbonitrile 5 gives the 9-amino acridine 5a via a conjugated imine, which
undergoes intramolecular cyclization. The BF3•OEt2 promoted dissociation of aryl azides to aryl
nitrenium ions is compared with those promoted by AlCl3 or a strong protic acid (TFA/TFSA
mixture).
