Download PDF Opens in a new window. Article suggestions will be shown in a dialog on return to ScienceDirect. ... Please enable JavaScript to use all the features on this page. ... An efficient use of triphosgene, as an acid activator, for the synthesis of substituted azetidin-2-ones via ketene–imine cycloaddition reaction using various acids and imines have been described. ... An efficient use of triphosgene, as an acid activator, for the synthesis of substituted ...