New reaction in pyrimidine series
The reaction proceeds by a double rearrangement scheme. First, as usual, the reagent adds to the C~6)-atom of the pyrimidine ring. This is followed by ring opening in adduct II, and closure ol a new ring with the participation of an electron-excess pyrimidine nitrogen atom and the carbonyl group of pyrazolone, into betaine III. Then, there is no aromatization of betaine III to pyranolopyridine, as in several similar cases [I, 2], but a repeated cyclization by a scheme of a sigmatropic rearrangement, leading to oxime IV. This reaction is completely new, not only for pyrimidine bases, but also for nitrogen-containing heterocycles, in general. A very remote analogy can be found in one single source only [3].