1.2.3- Triazolo pyrimidines synthesis

An example of synthesis A is that of 5-methyl-1,2,4-triazolo[l,5-a] pyrimidin-7-on (MOT) (3) by Bulow and Haas (09CB4638) given in Scheme 1. This reaction is a pyrimidine synthesis The C3-synthon condenses with a N—C—N moiety, which is a part of an AT. Apparently the reaction passes through the nonisolable intermediate 2 (Section II,A,2). 

Conventional polystyrene isocyanates have been successfully utilized for nucleophile scavenging in the synthesis of pharmaceutically attractive molecules. Player and coworkers have reported the use of conventional resin-bound isocyanates in the scavenging of amines in the synthesis of an 80-member library of triazolo-pyrimidines with purities greater than 90% (Scheme 8.2) [6]. 

Scheme 8.2 Utilization of PS-isocyanate for amine scavenging in Triazolo pyrimidine library synthesis.

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. 

Another synthesis of -triazolo [4,5-d] pyrimidines described first by Benson et and by Hartzel and Benson also involves closing... 

A combination of the preceding type of synthesis and of cyclization of 4-amino-5-arylazopyrimidine can be seen in the novel procedure of Richter and Taylor. Proceeding from phenylazomalonamide-amidine hydrochloride (180), they actually close both rings in this synthesis. The pyrimidine ring (183) is closed by formamide, the triazole (181) one by oxidative cyclization in the presence of cupric sulfate. Both possible sequences of cyclization were used. The synthetic possibilities of this procedure follow from the combination of the two parts. The synthesis was used for 7-substituted 2-phenyl-l,2,3-triazolo[4,5-d]-pyrimidines (184, 185). An analogous procedure was employed to prepare the 7-amino derivatives (188) from phenylazomalondiamidine (186). 

Tisler and his group published the first synthesis of the parent unsubstituted l,2,4-triazolo[l,5-c]pyrimidine 4 by transforming 4-aminopyrimidine 1... 

Studies by Almerico and co-workers into the synthesis of annelated l,2,3-triazolo[l,5- ]pyrimidines have led to an efficient method for the formation of the five- and six-membered rings onto a substituted pyrrole in good yield <2002T9723>. The reaction proceeds initially via a 1,3-dipolar cycloaddition between the azide group of 300 and the... 

Two types of addition to pyrimidine bases appear to exist. The first, the formation of pyrimidine photohydrates, has been the subject of a detailed review.251 Results suggest that two reactive species may be involved in the photohydration of 1,3-dimethyluracil.252 A recent example of this type of addition is to be found in 6-azacytosine (308) which forms a photohydration product (309) analogous to that found in cytosine.253 The second type of addition proceeds via radical intermediates and is illustrated by the addition of propan-2-ol to the trimethylcytosine 310 to give the alcohol 311 and the dihydro derivative 312.254 The same adduct is formed by a di-tert-butyl peroxide-initiated free radical reaction. Numerous other photoreactions involving the formation by hydrogen abstraction of hydroxyalkyl radicals and their subsequent addition to heterocycles have been reported. Systems studied include 3-aminopyrido[4,3-c]us-triazine,255 02,2 -anhydrouri-dine,256 and sym-triazolo[4,3-fe]pyridazine.257 The photoaddition of alcohols to purines is also a well-documented transformation. The stereospecific addition of methanol to the purine 313, for example, is an important step in the synthesis of coformycin.258 These reactions are frequently more... 

A rapid synthesis of trisubstituted l,2,4-triazolo[4,3-b]pyridazines has been devised to give selective variation of the three substituents through combinations of silicon-directed anion formation, palladium-catalyzed couplings and SnAt displacements <00TL781>. The synthesis of new l,2,4-triazolo[l,5-a]pyrimidines <00M1435>, 1,2,3-triazolo[4,5-(f]... 

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