Ketene O, S-acetals have been prepared by condensation of malononitrile 1 with chlorothionoformate esters 2 (X O) in the presence of two equivalents of sodium hydride followed by alkylation of the intermediate thiolate anion 3. In a similar manner a number of unsymmetrical ketene S, S-acetals were synthesised via thioacylation of 1 with chlorodithioformate esters 2 (X S). The reaction of the ketene O, S-acetals with ...