Abstract Enones (Z)-3-methyl-(Z)-3-chloromethyl-and (Z)-3-bromomethyl-4-R-3-buten-2-one (R= n-pentyl, phenyl, 2′-and 4′-chlorophenyl, 3′-and 4′-nitrophenyl, 4′- methoxyphenyl) were synthesized and subjected to reduction by the microorganisms Saccharomyces cerevisiae andGeotrichum candidum. Whereas the bioreduction of 3-methy- 4-R-3-buten-2-ones afforded the corresponding (S)-4-R-3-methybutan-2-ones, the ...