 If the ylide carbon is substituted with an electron @-@ withdrawing group ( EWG ) , the reagent is referred to as a stabilized ylide . These , similarly to sulfoxonium reagents , react much slower and are typically easier to prepare . These are limited in their usefulness as the reaction can become prohibitively sluggish : examples involving amides are widespread , with many fewer involving esters and virtually no examples involving other EWG 's . For these , the related Darzens reaction is typically more appropriate . 
