By the reaction of acetylacetone and arylazoacetylacetones with 4-iminothiazolidin-2-one thiazolo [4,5-b]pyridines were obtained in good yields. Optimum reaction conditions were chosen and some properties of compounds obtained were studied.Five-membered heterocycles fused to the pyridine ring attract constant attention since many compounds of this class possess the biologic action. Thiazolo [4,5-b]pyridines are among the least accessible and in turn poorly understood representatives of this class of organic substances. The information on their biological activity is also insuffi cient. In particular, among this type compounds substances were found possessing fungicidal action [1], antagonists of Н3-histamine receptors [2], antagonists of metabotropic glutamate receptors 5 (mGluR5) [3] of high inhibitor activity with respect to the receptors of the epidermal growth factor [4] and a number of other enzymes [5,6].Two fundamentally different approaches exist with respect to the synthesis of the thiazolo[4,5-b]pyridine system. The fi rst one is based on the fusion of the thiazole ring to the pyridine. Here 2-aminopyridines [7], thioureas[8-10], or thiocarbamates [11] are used as initial compounds. The second procedure of the pyridine ring fusion is underlain by a three-component condensation of derivatives of 4-aminothiazoles and 4-aminoselenazoles with aromatic or aliphatic aldehydes and the Meldrum's acid [12]. At the use in the reaction with 2,4-diaminothiazoles of ethyl acetoacetate and acetylacetone 2-amino-5,7-dimethylthiazolo[4,5-b]pyridines and 2-amino-7-methyl-4Н-thiazolo[4,5-b]pyridin-5-ones were obtained respectively [13]. Examples are also known of the synthesis of 1,3-thiazolo[4,5-b]pyridine derivatives with the use of solid-phase carriers [14] and with the application of dominoreactions [15].We report here on a convenient method of preparation of 3H-thiazolo[4,5-b]pyridin-2-one derivatives. We used 4-iminothiazolidin-2-one (I) as the initial compound [16] that was reacted with acetylacetone (II). We optimized the conditions of this reaction that made it possible to obtain 5,7-dimethyl-3H-thiazolo[4,5-b]-pyridin-2-one (IV) in good yield. The best results were observed at keeping the reagents mixture in methanol in the presence of sodium methylate over 5 days. Similar procedure was described earlier in patent [17], but due to the low yield the method had no preparative value.We also studied the behavior in this reaction of acetylacetone arylazo derivatives IIIа-IIIg (Scheme 1). Under the chosen conditions the corresponding 6-arylazo-5,7-dimethyl-3H-thiazolo[4,5-b]pyridin-2-ones Vа-Vg formed in good yields. These substances were orange or red crystalline powders well soluble in DMF and DMSO, sparingly soluble in water and the other organic solvents.The structure of compounds obtained was proved by NMR spectra. For instance, the proton signals of the methyl groups of the pyridine ring are observed at 2.42-2.46 and 2.49-2.87 ppm respectively, and of NH groups, in a relatively wide range of 9.78-14.29 ppm.Some...
