A-Alkylpyrazinium

Ring nitrogens in pyrazines and the benzo derivatives react with electrophiles to form quaternary ammonium species such as iV-alkylpyrazinium salts and pyrazine iV-oxides. N-Alkylation has generally been performed by treatment with a reactive alkyl iodide. The N-1 nitrogen in 2(l//)-pyrazinone 5 is methylated using chloro(chloromethyl)dimethyl-silane followed by desilylation with cesium fluoride to yield l-methyl-2(l//)-pyrazinone <2000TL4933>. 

In the present study, [N-Alk-Pz](TCNQ)m and [N-Alk-Pz](MTCNQ)m salts have been synthesized, with Aik for CnH2n+i n = 1, 2,...5 m 1,2. Aldrich- KodxLCQ pyrazine was used without any additional purification, while TCNQ and MTCNQ were refined by vacuum zone sublimation. Iodide alkyls were synthesized by the reaction of corresponding alcohols with phosphate tri-iodide followed by a distillation in inert atmosphere. To obtain alkylpyrazinium iodides, the quatemization reaction was used ... 

Bifunctional nucleophilic compounds can add to TV-alkylpyrazinium salts, and the benzo fused pyrazino[2,3-e][l,3,4]thiadiazine (471) as well as the benzo fused pyrazino[2,3-e]-l,2,4-oxadiazine (472) can be made by this method (Scheme 40). A closely related reaction is exemplified by the preparation of the pyrazino[2,3-e]-1,2,4-triazine (473) (Equation (94)) <87KGS557, 87KGS1118). The pyrimido[5,4-c][l,2,5]oxadiazine (475) can be prepared by treatment of the uracil derivative (474) with isoamyl nitrite (Equation (95)). Presumably the reaction proceeds by cyclization of an initially formed 5-nitrosopyrimidine intermediate (64ZC454). 

Note Alkylpyrazinium salts (or corresponding ylides) lend themselves to cy-clization or cycloaddition, as typified in these examples. l-Acetonyl-2,3-dfinethylpyrazinium bromide (358) (made in situ) gave 1,8-di-methylpyrrolol 1,2-a pyrazinc (359) (NaHC03, H20, reflux, 30 min 41%) 794 also analogues likewise.328 794 1571... 

NO is one of the classical strong Jt acceptors (3,4) and one of the very few Hgands with a positive charge other cationic % acceptor ligands are JV-alkylpyrazinium (Rpz ) and related quatemized heterocycles (5). 

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