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, 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.[1]

The reaction was discovered as part of a synthetic route to certain prostanoids.[2] 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.[3] 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.[1] A competing side-reaction is deinsertion from the acyl metal hydride:

RCH2C(O)MH → RCH2M(CO)H

This 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.[4][5] A true asymmetric synthesis was also described.[6][7] Both conversions employed rhodium catalysts and a chiral diphosphine ligand. In one application the ligand is Me-DuPhos:[8]

References

  1. 1 2 Michael C. Willis Transition Metal Catalyzed Alkene and Alkyne Hydroacylation Chem. Rev. 2009 doi:10.1021/cr900096x
  2. ↑ Synthetic studies on prostanoids 1 synthesis of methyl 9-oxoprostanoate K. Sakai, J. Ide, O. Oda and N. Nakamura Tetrahedron Letters Volume 13, Issue 13, 1972, Pages 1287-1290 doi:10.1016/S0040-4039(01)84569-X
  3. ↑ Transition-Metal-Promoted Aldehyde-Alkene Addition Reactions Charles F. Lochow, Roy G. Miller J. Am. Chem. Soc., 1976, 98 (5), pp 1281–1283 doi:10.1021/ja00421a050
  4. ↑ The Asymmetric cyclisation of substituted pent-4-enals by a chiral rhodium phosphine catalyst Brian R. James and Charles G. Young J. Chem. Soc., Chem. Commun., 1983, 1215 - 1216, doi:10.1039/C39830001215
  5. ↑ Catalytic decarbonylation, hydroacylation, and resolution of racemic pent-4-enals using chiral bis(di-tertiary-phosphine) complexes of rhodium(I) Brian R. James, and Charles G. Young Journal of Organometallic Chemistry Volume 285, Issues 1-3, 16 April 1985, Pages 321-332 doi:10.1016/0022-328X(85)87377-0
  6. ↑ Asymmetric cyclization reactions by Rh(I) with chiral ligands Yukari Tauraa, Masakazu Tanakaa, Kazuhisa Funakoshia and Kiyoshi Sakai Tetrahedron Letters Volume 30, Issue 46, 1989, Pages 6349-6352 doi:10.1016/S0040-4039(01)93891-2
  7. ↑ Asymmetric cyclization reactions. Cyclization of substituted 4-pentenals into cyclopentanone derivatives by rhodium(I) with chiral ligands Yukari Taura, Masakazu Tanaka, Xiao-Ming Wu, Kazuhisa Funakoshi and Kiyoshi Sakai Tetrahedron Volume 47, Issue 27, 1991, Pages 4879-4888 doi:10.1016/S0040-4020(01)80954-6
  8. ↑ Synthesis of D- and L-Carbocyclic Nucleosides via Rhodium-Catalyzed Asymmetric Hydroacylation as the Key Step Patricia Marce, Yolanda Dıaz, M. Isabel Matheu, Sergio Castillon Org. Lett., 2008, 10 (21), pp 4735–4738 doi:10.1021/ol801791g
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