A new and general synthesis of ketene S, S-thioacetals (1) and ketene OS-thioacetals (6) which involves the Horner-Wittig reaction of carbonyl compounds with the metallated S, S- and O, S-thioacetals of formyl-phosphonates (4 and 5) is described. The Horner-Wittig reaction of 4 with aromatic aldehydes can be carried out under two-phase conditions. The generation of the carbanions from 4 and 5 as well as the course of their reaction with ...