Allylation

Allylation is the enantioselective, iridium-catalyzed addition of an allyl group to an alcohol or aldehyde, producing a secondary homoallylic alcohol as a consequence. When employing aldehyde reactants, primary alcohol dehydrogenation or hydrogen transfer from 2-propanol is the mechanism of the Krische allylation. The Krische allylation allows for the direct conversion of primary alcohols to secondary homoallylic alcohols without the need of preformed allyl metal reagents, in contrast to other allylation techniques (precluding alcohol to aldehyde oxidation). The production of polyketide natural compounds typically uses enantioselective carbonyl allylations. Hoffmann reported the first asymmetric carbonyl allylation in 1978 using an allylborane produced from camphor and a chiral allylmetal reagent. Later, Kumada, Roush, Brown, Leighton, and others produced more chiral allylmetal reagents.