Reactions of A-Alkylpyrazinium Salts

The few recently described reactions of A-alkylpyrazinuim salts are typified in the following examples  

3-Cyano-5-(3,4-dimethoxyphenyl)-l-methylpyrazinium iodide (356) gave 6-(3,4-dimethoxyphenyl)-4-methyl-4,5-dihydro-2-pyrazinecarbonitrile (,357) [ Hantzsch ester (diethyl 2,6-dimethyl-l,4-dihydro-3,5-pyridinedicar-boxylate) (1 mol), MeCN, 20°C, 3 h 80% or NaBH4, MeCN, 20C, 30 min 83%], and thence 6-(3,4-dimethoxyphenyl)-4-methyl-l,4,5,6-tetrahydro-2-pyrazinocarbonitrile (357a) (repeat procedures for 24 and 3 h. respectively, both affording —72%)  

Also an unsuccessful attempt to reduce l-benzyl-2,3-diphenylpyrazinium bromide with TiCl,.  

Note Alkylpyrazinium salts (or corresponding ylides) lend themselves to cyclization or cycloaddition, as typified in these examples. 

Pyrazinium-l-dicyanomethylide (360) gave 7,8-bis(trimethylsilyl)pyrrolo[l,2-fl] pyrazine-6-carbonitrile (362) via the dicarbonitrile intermediate (361) (Mc,Si( =( SiMc,. PhMe, reflnx, 1 h 1% ) -  

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 

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