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DOI: 10.1055/sos-SD-016-00919

Sato, N.Science of Synthesis, (200416797.

The most important organometallic forms of electron-deficient heteroaromatics are the organolithium compounds; the formation of these in the pyrazine series is discussed in Section Pyrazinyllithium complexes react with a variety of reagents, therefore they are versatile intermediates for the synthesis of otherwise inaccessible pyrazine derivatives 188 (Scheme 66). The exchange of ring hydrogen with deuterium is realized by quenching of the lithiated pyrazines 139 with deuterated solvent (Scheme 41, Section Pyrazinyllithiums 139 undergo transmetalation with zinc(II) chloride[‌303‌] or tributyltin chloride.[‌226‌,‌233‌] The organozinc compounds couple with iodobenzene in the presence of tetrakis(triphenylphosphine)palladium(0) to afford phenylpyrazines; cross-coupling is often improved by sonication. (Trimethylsilyl)pyrazines are generated by simultaneous addition of metalating agent and chlorotrimethylsilane to a solution of the substrate.[‌222‌,‌226‌,‌227‌,‌231‌,‌233‌] Electrophilic substitution on pyrazinyllithiums 139 provides a variety of pyrazine derivatives (Scheme 66), for example methylpyrazines,[‌227‌,‌233‌] (trifluoromethyl)pyrazines,[‌304‌] pyrazinemethanol derivatives,[‌222‌,‌226‌,‌227‌,‌229‌,‌231‌,‌233‌‌235‌] pyrazinecarbaldehydes,[‌222‌,‌223‌,‌226‌,‌227‌] acylpyrazines,[‌223‌,‌226‌,‌227‌] and pyrazinecarboxylic acids.[‌222‌,‌227‌] In addition, heteroatom functionalities can be similarly introduced, for example chloropyrazines are prepared by treatment of pyrazinyllithiums 139 with hexachloroethane,[‌226‌,‌233‌] and iodopyrazines are similarly synthesized with iodine.[‌223‌,‌226‌,‌227‌,‌233‌,‌235‌] (Phenylsulfanyl)pyrazines are obtained by treatment of pyrazinyllithiums 139 with diphenyl disulfide.[‌226‌,‌227‌,‌233‌] When tosyl azide is used as the electrophile, azidopyrazine is produced.[‌228‌] Grignard derivatives of pyrazines can be prepared (Section and coupled with an aldehyde to afford low to moderate yields of pyrazinemethanol derivatives.[‌305‌]

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