Oximes of glucose, xylose, lactose, fructose, and mannose have been prepared. Nitrosation of the oximes of glucose, xylose, and lactose with NaNO2/HCl afforded 2‐(β‐glycopyranosyl)‐1‐hydroxydiazene‐2‐oxides, which were isolated as salts 13, 22, and 28. Nitrosation of fructose oxime 29 furnished fructose, whereas nitrosation of mannose oxime 30 with NaNO2/HCl afforded the 1‐hydroxy‐2‐(β‐d‐mannopyranosyl)diazene‐2‐oxide 32, from which the p‐anisidinium salt 31 and the sodium salt 33 were prepared. However, nitrosation of 30 with isopentyl nitrite in aqueous solutions of CsOH or KOH resulted in the formation of the 2‐(α‐D‐mannofuranosyl)‐1‐hydroxydiazene‐2‐oxide salts 34 and 35, respectively. Methylation of the ammonium 2‐(β‐D‐glucopyranosyl)‐1‐hydroxydiazene‐2‐oxide 13 yielded the 1‐methoxy compound, which was benzoylated to afford the tetra‐O‐benzoate 14 a, the structure of which was confirmed by X‐ray diffraction analysis. From the glucose O‐methyloximes 15 and 16 the N‐methoxy‐N‐nitroso‐2,3,4,6‐tetra‐O‐acetyl‐β‐D‐glucopyranosylamine 18 was prepared. The structure of this compound was confirmed by X‐ray diffraction analysis. Treatment of acetobromoglucose with cupferron furnished the 1‐(2,3,4,6‐tetra‐O‐acetyl‐β‐D‐glucopyranosyloxy)‐2‐phenyldiazene‐2‐oxide 20.
The reaction of 2-aminothiazol-4(5H)-iminium salts with various 1,3-CCC-dielectrophiles was investigated. As a result, a set of diverse thiazolo [4,5-d]pyridines were obtained. The scope and limitation of the approach is described.Compounds containing the thiazolo[4,5-d]pyridine structural unit have been shown to possess antibacterial, 1a,b and antisecretory 1c activity. They also can be used as a nonimidazole histamine H3-antagonists. 1d The thiazolo[4,5-d]pyridine system can be assembled through the annulation of a thiazole cycle to pyridine 2 or vice versa. 3,4 It has been shown that reaction of aminothiazoles with 1,3-dielectrophiles leads to thiazolo[4,5-d]pyridines in preparative yields; however, the scope and limitation of this method has not been investigated in detail.Current studies 5 were undertaken in order to develop a facile methodology for the synthesis of thiazolo[4,5-d]pyridines, starting from 5-unsubstituted 4-aminothiazole derivatives 1-3 and 1,3-CCC-dielectrophiles 4-18 ( Figure 1).Amines 1 and 2, generated in situ from their stable hydrochlorides (NaOAc, AcOH), 6 reacted with fluorine-containing 1,3-diones 4-6 to give thiazolo[4,5-d]pyridines as individual isomers 19 and 20 in 77-85% yield. The structure and purity of compounds 19 and 20 was unambiguously shown by GC-MS and NMR. Similarly bis(trifluoromethyl) derivative 19c was synthesized starting from 4c as a model compound for spectral investigation (Scheme 1, Table 1).Diaminothiazoles 1 reacted with diones 4a, 7, and 8 to give mixtures of the corresponding regioisomers 21-26, which were characterized by GC-MS and 19 F NMR spectrometry. The fluorine atoms of compounds 21, 22, 23, and 24 emerge in 19 F NMR spectra at d = -65, -68, -115.7, and -113.3, respectively. Cyclic diketone 18, reacted similarly to 4a to give regioisomers 27 and 28 in a 3:1 molar ratio (GC-MS).The formation of the g-isomers suggests that the initial attack of the trifluoromethyl-containing diketone occurs at the carbon atom of the thiazole cycle and the reaction proceeds via intermediates 31, 32, and 33 ( Figure 2). A 19 F NMR study revealed that the reaction of in situ generated amines 1 and 2 with trifluoromethyl-substituted 1,3-diones proceeds through the formation of pyridine hydrates 32 (d = -81), which, however, were too unstable to be isolated. Intermediate 33 was isolated; however it appeared to be unstable upon storage.
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