A new tautomeric zwitterion form of 2-acylamino-4H-1,3,4-oxadiazino[5,6-b]quinoxalines in solution

The reaction of 2-acylamino-8-chloro-4-methyl-4H-1,3,4-oxadiazino[5,6-b]quinoxalines 2a-d with methyl iodide/base gave the 8-chloro-4,10-dimethyl-4H-1,3,4-oxadiazino[5,6-b]quinoxaline-10-ium-2-acylamidates 4a-d, respectively. Comparison of the nmr spectral data between compounds 2a-d and 4a-d in deuteriodimethyl sulfoxide or in deuteriotrifluoroacetic acid established that compounds 2a-d existed as the zwitterionic tautomers 2'a-d in solution.