By Interconversion of Simple Alkyl Substituents

Alkyl-, alkenyl-, or alkynylpyrazines [usually with no functional groups attached to the alkyl substituent(s)] may be converted into other such pyrazines in several ways, as illustrated in the following examples  

5-Dimethyl-3-phenylethynylpyrazine (150) gave 2,5-dimethyl-3-styrylpyrazine (150a) [H2, Lindlar catalyst (Pd/CaC03, Pb-deactivated), C6H14, 20°C 97% or LiAlH4, THF, reflux, 4 h 20%].96 

In contrast, methyl 5-(pent-l-ynyl)-2-pyrazinecarboxylate (151, R = C CPr) gave methyl 5-pentyl-2-pyrazinecarboxylate (151, R = CH2Bu) (H2, Pd/C, MeOH, 20°C 94%).93 Also other examples.969,1588 

2-Methylpyrazine (152) gave 2-benzylpyrazine (153) [NaNH2, NH3 (liquid), trace Fe(N03)3, -78°C then PhBr j 15 min 53%]199 or several other 2-alkylpyrazines likewise.886 

6-Tetramethylpyrazine gave l,2-bis(3,5,6-trimethylpyrazine-2-yl)ethane (154) Pr 2NLi, Et20—C6H14, 0°C, 1 h then I2 j, 0°C, 30 min 31%) also homologues likewise.1128 

5-Dimethylpyrazine gave 2,5-distyrylpyrazine (PhCHO, BzuO, reflux, no further details).  

---