The reaction between the heteroaromatic N-oxides 1a, 1b and 1c with dimethyl acetylenedicarboxylate or methyl propiolate furnishes 1,3-benzodiazepines, the products of ring transformations of primarily formed cycloadducts. The structures of 8a and 10a have been confirmed by X-ray crystallographic analysis. The aldonitrone 1c also reacts with N-methylmaleimide and with phenyl vinyl sulfone to furnish the first examples of primary cycloaddition products from quinazoline 3-oxides.
Heaney, F., Lawless, E., Mahon, M., McArdle, P., & Cunningham, D. (2006). 1,3-Dipolar character of 2-vinyl quinazoline 3-oxides; first and second generation cycloaddition products. Organic and Biomolecular Chemistry, 4(12), 2408-2416. https://doi.org/10.1039/b602423h