1, 4-Addltion reaction of lithiated methyl dithioacetate with alpha,-beta-disubstituted enones affords diastereomeric 5-oxodithioalkanoates. Syn configuration was assigned to the major diastereomer by chemical correlation. High diastereoselectivities were obtained with 2, 2, 4- trimethyl-4-hexen-3 one and 2-ethylldenecycloalkanones, making this reaction useful for selective synthesis of acyclic or semi-cyclic chains with 1, 2-adjacent asymmetric carbons. ...