Ea. Filatova et al., 2-Trifluoromethylperimidines with electron-withdrawing groups at the 6(7)-position: a case of extremely hindered annular prototropy, MENDELEEV C, (5), 2000, pp. 178-180
In solutions of 6(7)-formyl-, 6(7)-acetyl- and 6(7)-p-toluenesulfonyl-2-tri
fluoromethylperimidines in non-polar solvents, both of the NH tautomers wer
e detected using H-1 NMR spectroscopy even on heating up to 130 degreesC.