Thiazoles azido

Arylsulfonylbenzimidoyl chlorides, with aminothiazoles, 50 Arylsulfonyl halides, 98, 115 Azide, with azothiazoles, 111 to carbamate, 16 Curtius rearrangement of, 15, 16 See also Sodium azide Azido thiazoles, 113 azidothiazole-thiazolotetrazole, 113 reactions of, 113... 

Azido-thiazole and -benzothiazole exist in equilibrium with a corresponding thiazolo[2,3-e]tetrazole form (Scheme 9). In the case of 2-azidobenzothiazole, at 20 °C in dioxane about the same proportion of both tautomers exist in equilibrium (77CJC1728). 

Action of HSO3CI on 2-substituted thiazoles affords the 5-chlorosulfonyl derivatives (337, 338). Addition of 6-phenylthiazolo[2,3-e]tetra2ole to oleum opens the tetrazole ring to form 2-azido-4-phenyI-thiazolyl-5-sulfonic acid, isolated as its salt (339). 5-Chloro-sulphonyl derivative is obtained similarly by action of HSO,Cl. 

This conclusion was largely confirmed at the much higher (MP2/6-311G ) level of approximation for the case of interconversion of azido-azomethine and tetrazole forms of thiazole[3,2-d]tetrazole 312 (Scheme 118) (98JA4723). 

The remarkable stability of the thiazole ring allowed synthetic manipulations of the thiazolyl ketol acetates, which extended considerably the scope of the above C-formylation method of furanoses and pyranoses. Instead of the reductive removal of the acetoxy group, the /V-glycosidation of either a- or p-anomer 73 with TMSN3 afforded stereoselectively the azido galactopyranoside 75 in 88% isolated yield (Scheme 22) [77]. The cleavage of the... 

Ethyl 2-(2-amino-4-thiazole)-2-methoxyiminoacetate, 2995b iV-Ethylaniline, 2989 Ethyl azide, 0868 Ethyl 2-azido-2-propenoate, 1884 f Ethylbenzene, 2963 f Ethyl bromide, see Bromoethane, 0842... 

Further applications of nitrene cyclizations have also been reported in which the intermediate nitrene inserts into a 7r-deficient heterocycle or a nitrene on a -deficient nucleus inserts into a proximal carbon-hydrogen bond. In general, the preferred source of the nitrene is the photolysis or thermolysis of an azide. The versatility of this approach is shown in two syntheses of pyrrolo[3,2-J]thiazoles (selenazoles) (177), (178), (180) (Equations (52) and (53)). Thermolysis of the / -thiazolyl (selenazolyl)-a-azido-esters (176) or the / -(4-azido-5-thiazolyl)-x,/J-enones (179) affords these bicyclic heterocycles in excellent yields (79JHC1563, 92JCS(Pi)973>. The same strategy has also been... 

In five-membered a-azido N-heterocycles, the effect of the azole ring is completely in favor of the azide form. All azidoazoles which are known have spectroscopic properties typical of azido derivatives. However, an azidomethine unit as part of the thiazole and 1,3,4-thiadiazole rings may exist in either the cyclized or open-chain form under normal conditions both forms are usually detected (77AHC(2l)323, 75BSB1189). 

The intramolecular aza-Wittig reaction of azidothioesters provides a new approach to functionalized thiazolines <07AG(E)2701>. Coupling of protected amino acids 79 with azido thiols 80 provides thioesters 81, which are treated with triphenyl phosphine to afford thiazolines 17 in good yields. Similarly, the bis(thioester) 82 is converted into the bis(thiazoline) 19. These thiazolines are readily oxidized to the corresponding thiazoles (vide supra). 

JV-acetyl derivatives of these azidoimidazoles give a 3 2 mixture of azido and tetrazole forms. It has been suggested that the azide form is much more prevalant in azoles than in azines and thiazoles. Substituents affect the equilibrium and a shift to the tetrazole form is mainly governed by resonance electron withdrawal. Not only electron-withdrawing power, but the size of a substituent group can also affect the equilibrium, for in... 

When the azomethine group is part of an electron-deficient ring, such as pyridine, pyrimidine or thiazole, the compounds exist as tetrazoles in the solid state, and at equilibrium with the azido form in solution . The equilibrium constants depend on the solvent, the nature of the substituents and the temperature . 2-Azido-4,6-dimethylpyrimidine (288a) thus exists in equilibrium with tetrazolo-pyrimidine (288b). Its chemical behaviour is, however, in accord with the azide structure 288a, including dipolar addition reactions and nitrene reactions . 

Gleiches trifft auf die Uberfuhrung von 2-Amino-l,3,4-thiadiazinen in 2-Azido-l, 3-thiazole zu, wobei auBerdem durch Salpetersaure eine Modifizierung dcr Hydrazin- zur Azid-Gruppe erfolgt1767 z.B. ... 

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