2.3- Dicyanopyrazines

The conversion of DAMN into 2,3-dicyanopyrazines substituted in the 5-and 6-positions with various combinations of amino, cyano, chloro, and hydroxyl groups will be described in this section along with transformations of these initially formed materials into a variety of other multifunctional and fused ring pyrazines. 

DISN reacts with the electron-rich olefins 112 and 113 with complete retention of stereochemistry to give the 1,2,3,4-tetrahydropyrazines 114 and 115, respectively. Heat or acid converts either isomer to 2,3-dicyanopyrazine (116) (Scheme 40). 

The use of a, -diaminopropionic acid with a,0-dicarbonyl compoimds leads to pyrazinecarboxylic acids (351, 352), and diaminomaleonitrile (S3) gives 2,3-dicyanopyrazines (52, R = R = CN) (353, 355, 357). The condensation of a,/3-diamino compounds with a-keto esters has been shown to give 5-hydroxy-23-dihydropyrazines (51, R = OH) (340). 

Dicyanopyrazine with sodium methoxide in methanol with ammonia at reflux gave 5,7-diimino-6//-pyrrolo[3,4-i)]pyrazine (65) (1442) and 2,3-dicyano-5,6-dimethyl(and 5,6-diphenyl)pyrazine with hydrazine by the procedure of Patel and Castle (1339) gave 2,3-dimethyl(and 2,3-diphenyl)-5,8-diaminopyrazino[2,3-rfJ-pyridazine(s) (66) (1435). Fusion of 2-chloro-3-cyano-5,6-diphenylpyrazine with urea and thiourea was reported to give 4-amino-2-hydroxy(and mercapto)-6,7-diphenylpteridine (848). 

There are many examples of phthalocyanine derivatives, given the general designation azaphtha-locyanines, in which one (or two) of the carbons in each benzo unit is replaced by a nitrogen. The synthesis and properties of such macrocycles has been the subject of a detailed review.65 The physical properties of azaphthalocyanines differ from those of phthalocyanines. For example, they form hydrates readily, which complicates purification and they are protonated by, and soluble in, dilute acids. In addition, the Q-band in the UV/visible absorption spectrum is blue shifted relative to that of phthalocyanine.65 Importantly, the aza moiety can be quaternerized to give water-soluble or amphiphilic derivatives.66 Thus, the cyclotetramerization of symmetrical 2,3-dicyanopyrazines provides a route to isomerically pure 1,4,8,11,15,18,22,25-octaazaphthalocyanines. 

The ease of synthesis of substituted 2,3-dicyanopyrazines has allowed the preparation of 1,4,8,11,15,18,22,15-octaazaphthalocyanines with a variety of substituents attached to each of the remaining 2,3,9,10,16,17,23,24 positions (e.g., (lh)). These include alkyl and alkyloxy side-chains.67,68... 

This method yields the best results with symmetrical starting compounds. Diaminomaleonitrile 22 as a diaminoethene condenses directly with 1,2-diketones or reacts with y keto sulfoxides followed by dehydrogenation [157] yielding 2,3-dicyanopyrazines 23. 

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