Reversible pH-dependent cyclization of hydroxy-substituted gem-chloronitroso compounds to isoxazoline N-oxides and 5,6-dihydro-4H-1,2-oxazine N-oxides

Cyclization of hydroxy-substituted gem-chloronitroso compounds under the action of bases affords cyclic nitronates, namely, isoxazoline N-oxides and 5,6-dihydro-4H-1,2-oxazine N-oxides. The process is reversible, viz., the chloronitroso compounds are regenerated upon the action of hydrogen chloride on the cyclization products. A method for the synthesis of cyclic nitronates from aldols using the title reaction was developed. The cyclization mechanism was studied and the kinetic parameters of the process were determined using UV—Vis and IR monitoring and the results of quantum chemical calculations.