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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, often rhodium. It is almost invariably practice as an intramolecular reaction. With an alkyne in place of alkenes, the reaction product is an α,β-unsaturated ketone.
Contents
The reaction was discovered as part of a synthetic route to certain prostanoids. The reaction required tin tetrachloride and a stoichiometric amount of Wilkinson's catalyst. An equal amount of a cyclopropane was formed as the result of decarbonylation.
The first catalytic application was reported by Miller in 1976. In their reaction, treatment of 4-pentenal with Wilkinson's catalyst gave cyclopentanone. In this reaction the solvent was saturated with ethylene.
Another suitable catalyst is the salt Rh(dppe2)ClO4.
Reaction mechanism
In terms of the reaction mechanism, hydroacylation involves oxidative addition of the aldehydic carbon-hydrogen bond and complexation of the alkene. The order is often unclear. The alkene inserts into either the metal-acyl or the metal-hydride bonds. In the final step, the resulting alkyl-acyl or beta-ketoalkyl-hydride complex undergoes reductive elimination. A competing side-reaction is deinsertion from the acyl metal hydride:
RCH2C(O)MH → RCH2M(CO)HThis step can be followed by CO loss and reductive elimination of the alkane.
Asymmetric hydroacylation
Hydroacylation as an asymmetric reaction was first demonstrated in the form of a kinetic resolution. A true asymmetric synthesis was also described. Both conversions employed rhodium catalysts and a chiral diphosphine ligand. In one application the ligand is Me-DuPhos: