Synthesis of pyrazine via chemoselective reduction of β-keto-α-oximino ester using baker’s yeast

•Pyrazines were prepared from β-keto-α-oximino esters using baker’s yeast.•Baker’s yeast reduced oxime selectively over ketone.•β-Keto-α-amino ester might be a key intermediate toward pyrazines.•β-Keto-α-oximino amide reacted with baker’s yeast to give pyrazines too.•Pyrazines were prepared efficiently and eco-friendly by biocatalyzed reaction.