 Catalytic reagents have been less successful , with most variations suffering from poor yield , poor enantioselectivity , or both . There are also issues with substrate scope , most having limitations with methylene transfer and aliphatic aldehydes . The trouble stems from the need for a nucleophilic sulfide that efficiently generates the ylide which can also act as a good leaving group to form the epoxide . Since the factors underlying these desiderata are at odds , tuning of the catalyst properties has proven difficult . Shown below are several of the most successful catalysts along with the yields and enantiomeric excess for their use in synthesis of ( E ) -stilbene oxide . 
