text: In 1978, Hoffmann reported the first asymmetric carbonyl allylation using a chiral allylmetal reagent, an allylborane derived from camphor. Such methods utilize preformed allyl metal reagents. The approach is well developed using allyl boranes
   As illustrated by the Keck allylation, catalytic enantioselective additions of achiral allylmetal reagents to carbonyl compounds also are possible by organostannane additions. 
  Allylic boronate and -borane reagents have also been developed for enantioselective addition to carbonyls—in this class of reactions, the allylic boron reagent confers stereochemical control