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Hydroacylation

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Hydroacylation

Hydroacylation is a type of organic reaction in which an aldehyde is added over an alkene or alkyne bond. The reaction product is a ketone. The reaction requires a metal catalyst and intramolecular reaction is favored over an intermolecular one. With alkynes the reaction product is an cyclopentenone.[1]

The reaction was discovered by K. Sakai in 1972 as part in a synthetic route to certain prostanoids.[2] The reagent in this reaction was tin tetrachloride. With an stoichiometric amount of Wilkinson's catalyst in chloroform, acetonitrile or benzene an equal amount of a cyclopropane was formed as the result of decarbonylation.

The first catalytic application was reported by Miller in 1976 [3] in the reaction of 4-pentenal with Wilkinson's catalyst to form cyclopentanone. In this reaction the solvent was saturated with ethylene.

Cyclopentane ring-formation is favored, the reaction product of 5-pentenal is again a cyclopentanone. Another suitable catalyst is cationic rhodium compound Rh(dppe)ClO4

Reaction mechanism

In a general reaction mechanism step one in hydroacylation is oxidative addition of the metal into the aldehyde carbon-hydrogen bond followed by side-on addition of the alkene, then followed by reductive elimination. A lurking side-reaction is decarbonylation from the acyl metal hydride RCH2(CO)MH to the alkane RCH3 and M(CO) via the RCH2M(CO)H intermediate.

Asymmetric hydroacylation

Hydroacylation as an asymmetric reaction was first demonstrated by James and Young in 1983 (kinetic resolution) [4][5] and by Sakai in 1989 (true asymmetric synthesis) [6][7] both employing rhodium and a chiral diphosphine ligand. In one application the ligand is Me-DuPhos:[8]

References

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