O. B. Smolii

Acylamino-substituted vinylphosphonium salts in syntheses of derivatives of nitrogen heterocycles

The results of 25-year studies of acylamino-substituted vinylphosphonium salts (AVPOSs), accessible and unique reagents for various heterocyclizations, are summarized. The main synthetic routes to AVPOSs, their transformations into various heterylphosphonium salts, and dephosphorylation of these salts are considered in detail. Particular attention is given to interpretation of the reactivity of mesomeric phosphonium ylide-betaines of the heterocyclic series, derived from AVPOSs. The advantages of these reagents in preparative syntheses of phosphorus-free functional derivatives of azoles and azines are demonstrated. Based on these data, peculiar features of AVPOSs are revealed, and a general concept of phosphonium syntheses of heterocyclic compounds is substantiated.

Two Approaches to the Transformation of (Benzimidazol-2-ylmethyl)triphenylphosphonium Chloride into the Derivatives of Pyrimido[1,6-a]benzimidazole

The reaction of readily accessible (benzimidazol-2-ylmethyl)triphenylphosphonium chloride with acyl isothiocyanates in the presence of triethylamine, as well as consecutive treatment of the above phosphonium salt first with N,N-dimethylformamide dimethyl acetal and then with phenyl or allyl isothiocyanate gives two types of phosphorus-containing derivatives of pyrimido[1,6-a]benzimidazole with the thione group in position 3 or 1 of the condensed system. The structure of one of compounds of the first type, 3-thioxo-1-p-tolyl-3,4-dihydropyrimido[1,6-a]benzimidazol-4-ylidenetriphenylphosphorane, was determined by single crystal X-ray diffraction.

Phosphonium Ylides Stabilized with Cyano Group and 5-Acylamino-4-phenyl-2-thiazolyl Residue

Available ylide reagent Ph3P = C(CN)C(S)NH2 readily enters cyclocondensation with N-(chlorophenacyl)benzamide and its analogs. By this route were prepared new stabilized phosphonium ylides containing cyano group and the corresponding 5-acylamino-4-phenyl-2-thiazolyl fragment. All these compounds even under standard conditions are dephosphorylated under the action of hydrogen chloride in acetic acid to form 5-acylamino-4-phenyl-2-cyanomethylthiazoles in high yields. Their structure was proved by spectroscopic studies and independent synthesis.