(3+3)-Cycloaddition provides a reliable approach to create spirocycles. A new 1,2-oxazine-based scaffold is available via acid-promoted reaction of imidazole-4-one activated donor-acceptor cyclopropanes with nitrones. The performed detailed study of the reactivity of nitrones of various types reveal the main regularities of the process. A highly diastereoselective reaction is observed for N-methyl nitrones, derived from electron-deficient benzaldehydes.