Twenty-five acyloins were generated by biotransformation of aliphatic aldehydes and 2- ketocarboxylic acids using whole cells of baker's yeast as catalyst. Six of these acyloins were synthesized and tentatively characterized for the first time. Subsequent chemical reaction with 1, 2-propanediamine under mild conditions resulted in the formation of thirteen 5, 6-dihydropyrazines and six tetrahydropyrazines. Their odor qualities were evaluated, ...