Abstract
The first part of this review is devoted to correlation of the data of five foreign reviews and the original research and data of the author on the synthesis of mesoionic heterocycles that do not contain ionogenic substituents (heteroatoms) in the side chain. The compounds were classified as follows: mono-, bi-, and triheterocycles; sulfur-containing heterocycles; two-ring systems with one, two, or no nitrogen atoms in common and their condensed analogs. The preparation of betaine cations of methine dyes by three methods, viz., cyanine condensations of some quaternary salts and protonated azaindolizines and deprotonation of diquaternary salts of diheterylmethanes, is described in the second part of the review.
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