Synthesis of substituted [1,3]thiazolo[4,5-b]pyridines and [1,3]thiazolo[4,5-d][1,2,3]triazines

In this work, we described an easy preparation of substituted 4-amino-5-cyano-1,3-thiazoles. These compounds have been used as starting materials to obtain two classes of compounds. New substituted [1,3]thiazolo[4,5-e]pyridines were synthesized in one step via Friedländer reaction. Diazotation of 4-amino-5-cyano-1,3-thiazoles afforded 4-chloro[1,3]thiazolo[4,5-d][1,2,3]triazines in one step. The later was substituted by a secondary amine to obtain substituted 4-amino[1,3]thiazolo[4,5-d][1,2,3]triazines.     

Novel syntheses of thiazolo[3,2-b]-s-triazoles

The reaction of 2-amino-and 2-acylaminothiazoles with O-mesitylenesulfonylhydroxylamine resulted in the ready formation in the corresponding 3-aminium salts, which were converted into thiazolo[3,2-b]-s-triazoles in high yields.     

Protonation of imidazo[2,1-b]thiazole and thiazolo[2,3-f]purine

The protonation of imidazo[2,1-b]thiazole and thiazolo[2,3-f]purine was investigated by PMR spectroscopy. In CF₃COOH and D₂SO₄ the imidazothiazole forms a monocation, the structure of which corresponds to the addition of a proton to the nitrogen atom of the imidazole ring. In aqueous D₂SO₄ solutions, the thiazolopurine forms mono- and dications. The first protonation occurs at the nitrogen atom of the pyrimidine ring, while the second protonation occurs at the nitrogen atom of the imidazole ring. The effect of delocalization of the positive charge in the cations of the investigated compounds was examined.     

Synthesis of pyrido[2,1-b]- and thiazolo[2,3-b]purines

Some pyrido[2,1-b]- and thiazolo[2,3-b]purines, tricyclic compounds structurally related to [1,2,4]triazolo[1,5-c]quinazolines 1 have been synthesized with a view to study their possible adenosine and benzodiazepine receptors affinity.     

A new synthesis of thiazolo[3,2-a] pyrimidinones

5H-Thiazolo[3,2-a]pyrimidin-5-ones (V) have been prepared by S-alkylation of 6-methyl-2-thiouracil (Ib) with bromoacetone or bromoacetophenone followed by cyclization in sulfuric acid. By the same series of reactions, 2-thiouracil (Ia) gave rise to 7H-thiazolo[3,2-a]pyrimidin-7-ones (VI). The properties and structures of the intermediates and products are discussed.     

Synthesis of derivatives of thiazolo[2,3-i]purine

Thiazolo[2,3-i]purine and its 7,8-alkyl(aryl, heteryl)derivatives were obtained by the cyclodehydration of 7hydroxy-7, 8-dihydrothiazolo[2, 3-i)purine and 6--oxoalkyl (aryl, heteryl)thiopurines in the presence of phosphoryl chloride, sulfuric, and polyphosphoric acids.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 265–270, February, 1996.     

Synthesis of thiazolo[5,4-b]pyridine-2-carboxamides

A convenient procedure was developed for preparation of thiazolo[5,4-b]pyridine-2-carboxamides by oxidation of monothiooxamides synthesized from 3-aminopyridine.     

Benzologs of the thiazolo[3,2-a]pyridinium system

By use of concentrated sulfuric acid rather than hydrobromic acid as the cyclizing medium, good yields of the thiazolo[3,2-a]quinolinium ion and its derivatives may be obtained from α-(2-quinolylthio) ketones or acetals. In the same way, α-(1-isoquinolylthio) and α-(6-phenanthridylthio) ketones afford thiazolo[2,3-a]isoquinolinium and thiazolo-[3,2-f]phenanthridinium salts.     

Derivatives of the thiazolo[2,3-a]isoquinolinium system

The ketosulfides (IV) formed by the reaction of α-bromoketones with 2α-thiohomo-phthalimide (II) have been cyclized to form hydrogen-bonded, dimeric hemiperchlorates (V). Alternative products from the cyclization, 2-[2′-(carboxymethyl)phenyl]thiazoles (VII), may be cyclized with acetic anhydride to O-betaines (VI). The same betaines are obtained from the hemiperchlorates (V) by deprotonation. The ketosulfide hydrobromides (XIII) from α-bromoketones and 1-thio-3, 4-dihydroisocarbostyril (XII) give 5,6-dihydro-thiazolo[2,3-a]isoquinolinium salts (XV) on cyclization.     

Synthesis of 5H-[1,3]thiazolo[3,2-a]pyrimidin-5-one derivatives

The reaction of 2-aminothiazoles with ethyl acetoacetate in acetic or polyphosphoric acid gave a series of 5H-[1,3]thiazolo[3,2-a]pyrimidin-5-one derivatives which were nitrated with a mixture of nitric and sulfuric acid to 6-nitro-5H-[1,3]thiazolo[3,2-a]pyrimidin-5-ones, and the latter were reduced to the corresponding amines.     

MgO nanopowders catalyzed synthesis of pyrano[4,3-d]thiazolo[3,2-a]pyrimidine derivatives

A cubic phase of pure MgO nanopowders was prepared in an aqueous solution containing freshly squeezed orange juice with pulp and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared (FT-IR) spectroscopic techniques. The catalytic potential of MgO nanopowders was evaluated in preparation of pyrano[4,3-d]thiazolo[3,2-a]pyrimidine and chromeno[4,3-d]thiazolo[3,2-a]pyrimidines derivatives using the three simple methods including thermal, ultrasonic irradiation, and high-speed ball milling (HSBM) technique under solvent-free conditions. All products were successfully formed in high yields.     

Mass spectra of imidazo[2,1-b]thiazole and thiazolo[3,2-f]xanthene derivatives

The general principles of the mass-spectrometric disintegration of imidazo [2,1-b]thiazole and thiazolo[3,2-f]xanthene derivatives were established, and the characteristic fragments were identified. Disintegration proceeding with cleavage of the bonds in the thiazole ring of the 2(3)-ring system is characteristic of all of the investigated compounds. The cleavage of the S-C bonds, which are the weakest in the investigated systems, proceeds especially readily. Intense peaks of ions due to stepwise disintegration of the pyrimidine ring are also observed in the spectra of thiazoloxanthenes.     

Cyanine dyes from naphtho [1,2-6]thiazolo[3,2-d][1,4]thiazine

Deeply colored cyanine dyes have been synthesized from the previously unknown 3-methyl-12H-naphtho[1,2-b]thiazolo[3,2-d][1,4]thiazinium salts. It is assumed that the deep color of the new cyanines is connected with the conversion of the nonaromatic 1,4-thiazine ring in the dye molecule into an aromatic thiazine ring with three double bonds in a six-membered ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1282–1284, September, 1973.     

Novel one-step synthesis of thiazolo[3,2-b]1,2,4-triazoles

[reaction: see text] Reactions of chalcones 3a-f with bis(1H-1,2,4-triazolyl) sulfoxide 4 formed the thiazolo[3,2-b]1,2,4-triazoles 5a-f, which resemble closely some previously prepared COX-2 inhibitors. The structure of 5a was confirmed by X-ray analysis.