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Carbonyl allylation

Chemical reaction From Wikipedia, the free encyclopedia

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In organic chemistry, carbonyl allylation describes methods for adding an allyl anion to an aldehyde or ketone to produce a homoallylic alcohol.[1] The carbonyl allylation was first reported in 1876 by Alexander Zaitsev and employed an allylzinc reagent.[2]

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Enantioselective versions

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In 1978, Hoffmann reported the first asymmetric carbonyl allylation using a chiral allylmetal reagent, an allylborane derived from camphor.[3][4] Such methods utilize preformed allyl metal reagents. The approach is well developed using allyl boranes[5]

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As illustrated by the Keck allylation,[6] catalytic enantioselective additions of achiral allylmetal reagents to carbonyl compounds also are possible by organostannane additions.[7]

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[5]

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Catalysis

In 1991, Yamamoto disclosed the first catalytic enantioselective method for carbonyl allylation, which employed a chiral boron Lewis acid-catalyst in combination with allyltrimethylsilane.[8] Numerous other catalytic enantioselective methods for carbonyl allylation followed.[9][6] Catalytic variants of the Nozaki-Hiyama-Kishi reaction represent an alternative method for asymmetric carbonyl allylation, but stoichiometric metallic reductants are required.[10]

Whereas the aforementioned asymmetric carbonyl allylations rely on preformed allylmetal reagents, the Krische allylation exploits allyl acetate for enantioselective carbonyl allylation.[11] Selected methods for asymmetric carbonyl allylation are summarized below.

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Use in total synthesis

Carbonyl allylation has been employed in the synthesis of polyketide natural products and other oxygenated molecules with a contiguous array of stereocenters. For example, allylstannanation of a threose-derived aldehyde affords the macrolide antascomicin B, which structurally resembles FK506 and rapamycin, and is a potent binder of FKBP12.[12] The Krische allylation was used to prepare the polyketide (+)-SCH 351448, a macrodiolide ionophore bearing 14 stereogenic centers.[13]

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Older primary literature

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References

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