1.2.4- Triazolo pyrimidine-2-sulfonyl

With the invention of the aceto-hydoxy-add synthesis inhibitors (AHAS) the dominance of herbiddes that ad as photosynthesis inhibitors was dramatically broken - as it was also by the development of genetically modified herbicide tolerant crops. These especially important areas of research and development, from the 1990s up to now, are exemplified in Chapters 3 and 7. The development of 12 new sulfonyl urea herbicides launched since 1995 and the invention of four development compounds of the same chemical class, after the introduction to the market of twenty compounds already between 1980 and 1995, refleds the importance of this biochemical mode of adion for the herbicide market as well as the different chemistries found to be active at this target, such as imidazolinones, triazolo-pyrimidines, pyrimidinyl-carboxylates, and sulfonylaminocarbonyl-triazolinones. 

Oxidation of 2-mercapto-l,2,4-triazolo[l,5-c]pyrimidines (174) with chlorine or bromine in water (64BRP951652 65JCS3369), with hydrogen peroxide and chlorine (95MIP1), as well as with sodium chlorate in hydrochloric acid (94JMC2371) gave the corresponding 2-sulfonyl halide derivatives 175. Oxidation of the 2-alkylmercapto compounds 176 to the 2-alkylsufonyl derivatives 177 was made with ammonium peroxodisulfate and sulfuric acid... 

The target triazolo[l,5-c]pyrimidine sulfonamides 6 were prepared via coupling 7 with substituted benzenesulfonyl chlorides (Scheme 2). In these transformations, pyridine and a catalytic amount of dimethylsulfoxide (DMSO) were essential for the formation of 6. The reactive intermediate is believed to be the in situ generated sulhlimine 10 which allows for the relatively non-nucleophiKc amines to react with sulfonyl chlorides under mild conditions [7-8],... 

Synthetic routes leading to triazolo[l,5-c]pyrimidine sulfonanilides have been reviewed [4]. Scheme 2.4.1 shows a general synthetic route to the triazolo[l,5-cjpyrimidine sulfonanilides [5]. An appropriately substituted 4-hydrazino-2-methylthiopyrimidine is reacted with carbon disulfide followed by benzyl chloride to afford 3-benzylthio-5-methylthio-l,2,4-triazolo[4,3-c)pyrimidine (8). Compound 8 is then treated with methoxide to afford 2-benzylthio-5-methoxy-l,2,4-triazolo[l,5-c]pyrimidine (9). The benzyl sulfide (9) is oxidized to the sulfonyl chloride (10) by treatment with chlorine and water. The sulfonyl chlorides... 

The N-triazolo[l,5-c]pyrimidine sulfonamides and related compounds differ from their sulfonanilide counterparts by the orientation of the linkage between the triazoloazine and the aryl or heteroaryl ring. However, in most cases synthesis of sulfonamides is similar to the sulfonanilides, as the target molecules are formed by reaction of a sulfonyl chloride and an amine in the final step. Notably, the synthesis of arylsulfonyl chlorides account for much of the diversity in these molecules [32-36]. 

Scheme 2.4.4 outlines a general route for the synthesis of N-triazolo[l,5-a]pyrimidine sulfonamides (20) [48, 49]. 2-Amino-4,6-dimethoxypyrimidine (21) is reacted with thiocarbonyldiimidazole followed by hydroxylamine in the presence of a base to give 23, which is then reacted with various substituted benzene and pyridine sulfonyl chlorides (17 Scheme 2.4.3) in the presence of a catalytic amount of dimethyl sulfoxide and a base to give 20. 

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