This paper reports the synthesis of a new optically active synthon 6 for the asymmetricsynthesis of 19-norsteroids. Symmetric trione 9 obtained by the reaction of γ-carbonyl sulfo-xide 12b with 2-cthyl-1, 3-cyclopetanedione 8, was reduced asymmetrically by Saccharomycescerevisiae to (2R,3S)-(-)-14 and subsequently transformed into (2R,3S)-(+)-6 by a shortreaction sequence. The absolute configuration of the asymmetrical product, (2R, 3S)-(-)-14,was established by converting it into the known compound (2R, 3S)-(+)-17. This paper reports the synthesis of a new optically active synthon 6 for the asymmetrical synthesis of 19-norsteroids. Symmetric trione 9 obtained by the reaction of γ-carbonyl sulfo-xide 12b with 2-cthyl-1, 3-cyclopetanedione 8, was reduced asymmetrically by Saccharomyces cerevisiae to (2R, 3S) - (-) - 14 and the like and transformed into (2R, 3S) - (+) - 6 by a short reaction sequence. The absolute configuration of the asymmetrical product. (2R, 3S) ) -14, was established by converting it into the known compound (2R, 3S) - (+) - 17.