 If the ylide carbon is substituted with an electron @-@ withdrawing group ( <unk> ) , 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 <unk> sluggish : examples involving <unk> are widespread , with many fewer involving <unk> and virtually no examples involving other <unk> 's . For these , the related <unk> reaction is typically more appropriate . 
