A novel synthesis of 1,2-disubstituted 1,2-dihydroquinazoline 3-oxides 8 and the first ever examples of 1,3-dipolar trapping of these nitrones to homonuclear dipolarophiles is described. The new dipoles 8 reacted with N-methyl maleimide, generating diastereomeric adducts 14-16. In the reaction between 8 and dimethyl acetylenedicarboxylate, primary cycloadducts 17 and/or stable rearrangement products, azomethine ylides 18, are formed depending on the substitution pattern of the dipole. The structure of 18c is unambiguously assigned by X-ray crystallographic analysis. An X-ray crystal structure determination is also presented for the cyclopropylisoxazoloquinazoline 22 formed by a [ 3 + 2] addition of 8a to 21, the dimethyl acetylenedicarboxylate tetramer.
Heaney, F., McCarthy, T., Mahon, M., & McKee, V. (2005). Bridgehead nitrogen heterocycles which contain the quinazoline moiety - synthesis and cycloaddition of 1,2-dihydroquinazoline 3-oxides. Organic and Biomolecular Chemistry, 3(24), 4351-4361. https://doi.org/10.1039/b511998g