A similar observation was made with the smaller crown ether (i.e. 12-crown-4, (12-c-4)) and switching to the potassium yldiide 1b-K in combination with 18-crown-6 (18-c-6) yielded the ketenyl anion in perfect selectivity (Entry 10). The efficiency of these reaction conditions was further confirmed with 1c-K which likewise selectively delivered the 2-K (Entry 11).