Farat O. Electrophilic rearrangements of six-membered heterocycles with geminal arrangement of nitrogen and/or oxygen atoms and reactions of the resulting products

The regularities of the rearrangement of 2,2-disubstituted pyrimidin-4-ones under the action of the Vilsmeier-Haack reagent to derivatives of acridines and quinolines have been established. The effect of the size of aliphatic annulated and spiro cycles on the conditions of the rearrangement course and the formation of the products of the different structure has been explained. It has been found that electrophilic rearrangement of spiroderivatives of 1,3-benz(naphth)oxazines with an average size of spirocycle (5-8 membered cycles) proceeds to formyl derivatives of xanthene. The reaction conditions have been affected by the electronegative substituents in the α-position to the oxygen atom, which was established in the numerical examples. Isomeric spiroderivatives of 3,1-benzoxazines have been recycled at room temperature with a quantitative yield to chloracridine or acridone derivatives under the action of the Vilsmeier-Haack reagent regardless of the presence of bromine atoms in the α-position to the nitrogen atom. A new electrophilic rearrangement of 1,3-benzodioxin-4-ones has been discovered, which, under the action of the Vilsmeier-Haack reagent, leads to a profound restructuring of the carbon skeleton with the formation of previously unknown xanthene derivatives containing in their structure a chlorine atom capable of nucleophilic substitution. Amidine moiety formyl derivatives of xanthene obtained by the rearrangement of 1,3-benz(naphth)oxazines fluoresce in the yellow-green region of the spectrum with a large Stokes shift (4300–5700 cm-1) and moderate quantum yields (0.07–28.94%). Two types of interaction of the dimethylamidine substituent with the xanthene framework have been proved: the π-amidine-xanthene coupling and the stereoelectronic interaction lp(N)→π*, despite its almost perpendicular arrangement relative to xanthene. The new dyes have been synthesized by the modification of the formyl group of the active CH-acids by the Knoevenagel reaction. They are characterized by high extinction coefficients (6.07–7.96x104 (M-1·cm-1)) and longer wavelength absorption maxima (531–667 nm) comparing to the initial aldehydes (~425 nm).