Isay synthesis

The main reaction of this type has been the reductive cyclization of nitropyridine derivatives carrying an o-amino ester or o-aminocarbonyl substituent. These cyclize in situ via the o-diamino derivative to give pyridopyrazines of known constitution, either for establishment of structure of products obtained in the ambiguous Isay synthesis (see Section 2.15.15.6.1), or in the synthesis of aza analogues of biologically active molecules. 

The synthesis of the pteridine ring system has been approached by two obvious routes one is the fusion of the pyrazine ring onto a pre-formed 4,5-diamino-pyrimidine, and the second, the elaboration of the pyrimidine ring on a pre-formed pyrazine. The first of these, the Isay synthesis, suffers from the disadvantage that condensation of the heterocyclic 1,2-diamine with an unsymmetrical 1,2-dicarbonyl compound... 

Diaminopyrimidines cyclocondense with symmetrical 1,2-dicarbonyl compounds to give pteridines 1 Gabriel-Isay synthesis) ... 

Gabriel-Isay synthesis (pteridine) Gabriel synthesis (thiazole) 207 Gassmann synthesis (indole) 135 Gattermann synthesis, HCN-free 509 Gewald synthesis (thiophene) 97 Graebe-Ullmann reaction 266 Guareschi synthesis (2-pyridone) 384... 

By far the most important reaction for the synthesis of pyridopyrazines is the reaction of diaminopyridines with two-carbon fragments, the pyridopyrazine equivalent of the well-known Isay reaction in the pteridine field. 

Since the structures of the Gabriel-Isay condensation products of 5,6-diaminopyrimidines with unsymmetrical 1,2-dicarbonyl or a-substituted monocarbonyl compounds are always ambiguous, the synthesis of 6- and 7-substituted pteridines by an unambiguous approach was and still is a necessity and an important challenge. 

Isay reaction, 2, 79-80 3, 259 Ismelin 7, 656 Isoalloxazine oxidation states, 1, 252 Isoaminopterin synthesis, 3, 327 Isoarsindolines, 1, 543-544 Isoarsinoline, tetrahydro-synthesis, 1, 552-553 stability, 1, 552 Isoascorbic acid structure, 4, 552 ( )-IsoavenacioIide synthesis, 1, 416 Isoazapenem synthesis, 1, 465 Isobacteriochlorin synthesis, 4, 419 Isobacteriochlorin, dimethyl-biosynthesis, 1, 105 Isobacteriochlorin, methyl-biosynthesis, 1, 105 Isobacteriochlorin, trimethyl-biosynthesis, 1, 105 Isobarbituric acid Mannich reaction, 3, 71 synthesis, 3, 133... 

Pteridine, 6,7-dimethyl-4-trifluoromethyl-structure, 3, 266 Pteridine, 6,7-dioxotetrahydro-electrochemistry, 3, 285 Pteridine, 6,7-diphenyl-Isay s synthesis, 3, 309 Pteridine, 6,7-diphenyl-7,8-dihydro-synthesis, 3, 312... 

Purine (6) itself is a colorless crystalline weak base which was first prepared by Fischer " the first synthesis using the Traubc condensation was reported by Isay. The Traube protocol is probably the best method to prepare purine, using pyrimidine-4,5-diamine as precursor and formic acid in an atmosphere of carbon dioxide or diethoxymethyl acetate as cyclizing reagents. 

In 2002 Isay-type condensations for synthesis of 6-substituted pterins, including pterin sugar derivatives and 2-substituted quinoxalines, were developed under microwave irradiation conditions [103]. Interestingly, the isomer-free 6-substituted pterins desired were obtained in moderate to good yields whereas mixtures of both 6- and 7-isomers (major) are usually formed when conventional Isay type condensations are used. 

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