Irina V. Shcherbakova

Benzo[c] Pyrlium Salts: Syntheses, Reactions, and Physical Properties

Publisher Summary This chapter demonstrates the wide potential for using the newly developed methods to synthesize 2-benzopyrylium salts and discusses in detail the numerous and unusual transformations of this class of oxygen cations in comparison with monocyclic pyrylium salts— that is, the study of the influence of benzo[c]annelation. Two benzoannelated analogues of the pyrylium cation are known as benzo[b]pyrylium (chromylium or I-benzopyrylium) and benzo[c]pyrylium (isochromylium or 2-benzopyrylium) salts. The reactions of 2-benzopyrylium salts can be divided into five groups: (1) reactions of substituents conserving the benzo[c]pyrylium system, (2) nucleophilic addition reactions, (3) deprotonation reactions, (4) cycloaddition reactions, and (5) dimerization and further transformation of dimmers. Moreover, the chapter discusses the physical properties of benzo[b]pyrylium salts and spectroscopic analysis. The ultraviolet spectral data on 1 -arylbenzo[c]pyrylium salts is dependent on the pH values. From the pH dependence of the spectra, pKa values of the salts were computed, and although the general trend of polarographic and spectrophotometric pKa values were similar the numerical values were markedly different.

Synthesis and some transformations of substituted 5,6-dihydro-4H-1,3-oxazines

Abstract Substituted 5,6-dihydro-4H-1,3-oxazines are prepared by the acid-catalyzed amidoalkylation of the terminal olefins. 5,6-Dihydro-4H-oxazines undergo further transformations involving the hetero-ring and/or the substituent leading to alkyl amino-substituted 5,6-dihydro-4H-1,3-dihydrooxazines and/or to ring-opened products, 3-hydroxypropylamides.

Tautomerism of heterocycles: Condensed five-six, five-five, and six-six ring systems with heteroatoms in both rings

Publisher Summary This chapter discusses several surveys done on pyrazino pyrimidines or pteridines with some focus on tautomerism. Limited data on other heterocycles is discussed in this chapter. Six–six condensed heterocyclic systems without a tautomeric functional groups do not exhibit prototropic tautomerism. The introduction of an oxo(thioxo)- and/or amino groups into the pteridine system and the appearance of at least one NH group in the ring leads to functional and/or annular tautomerism. Pteridine is formally the parent of three groups of compounds of particular interest because of their biological importance: pterins, lumazines, and flavins.

2-benzopyrylium salts. XXXVII. Oxygen analogs of reissert compounds : molecular structure and reactions with sodium hydroxide

Abstract The weak intensity of the CN stretching band in IR spectra for 1-cyanoiso chromenes is obviously determined by the steric position of the CN group in the molecule, as it was established by X-ray structural analysis for the cyanide addition product 2d of 1-isopropyl-3-methyl-2-benzopyrylium salts. Depending on the other substituent in position 1, 1-cyanoisochromenes in aqueous solutions of sodium hydroxide eliminate hydrogen cyanide 2a , b , e , undergo inter- 3a , b or intra-mlecular 2c , d recyclisation, or hydrolysis of the cyano group in 2f ; reaction products include α-naphthols 7c , e , β-naphthol 7d , acylchrysenes 5a , b , or the iso chromene-amide 11f , a stable 1-alkylideneisochromene 3e was obtained, and the intermediacy of 3-hydroxy-1-alkylideneiso chromenes was proved by their isolation in the cases of 10c , d

2-benzopyrylium salts. xxxi : Analogs of reissert compounds from 2-benzopyrylium salts and sodium cyanide

Abstract Nucleophilic addition of a cyanide anion to 2-benzopyrylium salts I takes place at the first position and leads to stable isochromenes II, which are oxygen analogs of Reissert compounds. The structure II was confirmed by IR, 1H-NMR and 13C-NMR spectra. The latter spectra reveal clearly the cyano group (which does not yield any observable stretching band) and give evidence for diastereotopic isopropyl carbons (unlike 1H-NMR spectra).

A Novel Synthetic Route to Dihydro- and α-Hydroxytetrahydro-furan Derivatives

Abstract 1-(3-Morpholinoprop-2-enyl)benzotriazole (1) provides a three carbon unit for the construction of dihydro- and tetrahydro-furan rings by one pot procedures. Lithiation of 1 followed by reaction with diaryl ketones gave 2,5-dihydro- and/or α-hydroxytetrahydro-furans, whereas successive reactions with iodoalkanes and diaryl ketones yielded 2,3-dihydrofurans.

Amidoalkylation of nonactivated terminal double bond in polyalkenes

Amidoalkylations of polybutenes and of ethene-propene copolymer, catalyzed by trifluoroacetic acid, result in 5,6-dihydro-4H-1,3-oxazino-substituted polyalkenes with the 2-position of the oxazine ring unsubstituted or occupied by a vinyl or a phenyl group. The vinyl-substituted dihydrooxazino polymers thus obtained readily add butylamine to the vinyl fragment yielding alkylamino-substituted derivatives.

A novel synthetic approach to ethers

1 -Methoxymethylbenzotriazole undergoes lithiation at the methylene group and the carbanion affords substitution products with various electrophiles. Grignard reagents replace the benzotriazole residues of some of the compounds thus obtained to give the corresponding methyl ethers.