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Carbocyanine dyes with an o-hydroxyaryl substituent in the meso position of the polymethine chain were obtained from o-hydroxybenzoyl derivatives of the Fischer base and heterocyclic methylene bases (1,3,3-trimethyl-2-methyleneindoline, 1-ethyl-4-methylene-1,4-dihydroquinoline, and 1-methyl-2-methylene-1,2-dihydroquinoline) in the presence of phosphorus oxychloride. The symmetrical indolenine dyes exist in the colorless spiropyran form in an alkaline medium. The unsymmetrical carbocyanines with a quinoline fragment do not form a spiro form and are deeply colored compounds; this is explained by their open dipolar structure.

Symmetric 2-pyrylo- and asymmetric (indo)(2-pyrylo)trimethinecyanines with substituents of different electronic nature in the pyran residue were synthesized. The influence of the conjugation effect and inductive effect on the characteristics of absorption bands of the synthesized dyes was analyzed by a quantum chemical calculation according to a common MO Hückel method.

It was established that homologs of orthoformic ester (orthoacetic and orthopropionic esters), in contrast to it, do not undergo reaction with substituted acetophenones and boron trifluoride etherate to give ?-alkylpyrylium salts; the products obtained are 2,4,6-triarylpyrylium tetrafluoroborates.

The pyrylium salts (I) are coupled with the benzaldehydes (II) to give the styrylpyrylium salts (III).

Condensation of salicylic aldehydes such as (I) with acetone, cyclopentanone or cyclohexanone yields arylidene ketones (III).

The cyanines (II) and (IV) are prepared by condensation of the pyrylium salts (I) with triethyl orthoformate or from (I) and the formylmethyleneindoline (III).

The o‐hydroxybenzoyl derivatives (I) of Fischer's base are treated with phosphoryl chloride and subsequently coupled with Fischer's base (III) to form the carbocyanine dyes (IV) which cyclize upon reaction with bases, producing mixtures of the isomeric spirochromenes (V) and (VI).