Reduction of α,β-unsaturated compounds

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A Pd/C-catalyzed hydrogenation using diphenylsulfide as a catalyst poison selectively reduces olefin and acetylene functionalities without hydrogenolysis of aromatic carbonyls and halogens, benzyl esters, and N-Cbz protective groups.
A. Mori, Y. Miyakawa, E. Ohashi, T. Haga, T. Maegawa, H. Sajiki, Org. Lett., 2006, 8, 3279-3281.

Pd/P(t-Bu)₃ is an efficient and mild catalyst for selective reduction of various alkenes under transfer-hydrogenation conditions leading to the corresponding saturated derivatives in good yields.
J. M. Brunel, Synlett, 2007, 330-332.

A new recyclable catalyst composed of palladium nanoparticles dispersed in an organic polymer was synthesized by a simple procedure from readily available reagents. This catalyst is robust, and highly active in many organic transformations including alkene and alkyne hydrogenation, carbon-carbon cross-coupling reactions, and aerobic alcohol oxidation.
C. M. Park, M. S. Kwon, J. Park, Synthesis, 2006, 3790-3794.

A system composed of nickel(II) chloride, lithium metal, a catalytic polymer-supported arene, and ethanol, has been efficiently applied to the conjugate reduction of various α,β-unsaturated carbonyl compounds under very mild reaction conditions.
F. Alonso, I. Osante, M. Yus, Synlett, 2006, 3017-3020.

An efficient and highly enantioselective conjugate transfer hydrogenation of α,β-unsaturated ketones is catalyzed by a salt made from tert-butyl valinate and a recently introduced powerful chiral phosphoric acid catalyst (TRIP).
N. J. A. Martin, B. List, J. Am. Chem. Soc., 2006, 128, 13368-13369.

The use of a chiral imidazolidinone catalyst has provided a new organocatalytic strategy for the enantioselective reduction of β,β-substituted α,β-unsaturated aldehydes to generate β-stereogenic aldehydes using ethyl Hantzsch ester as the hydrogen source. In addition, an acceleration of E-Z isomerization prior to selective E-olefin reduction allows the use of geometrically impure enals in this operationally simple protocol.
S. G. Ouellet, J. B. Tuttle, D. W. C. MacMillan, J. Am. Chem. Soc., 2005, 7, 32-33.

Selective conjugate reductions of α,β-unsaturated aldehydes were achieved in the presence of rhodium(bisoxazolinylphenyl) complexes as catalysts and alkoxyhydrosilanes as reducing agents.
Y. Kanazawa, H. Nishiyama, Synlett, 2006, 3343-3345.

A highly chemoselective conjugate reduction of electron-deficient Michael acceptors, including α,β-unsaturated ketones, carboxylic esters, nitriles and nitro compounds with PMHS in the presence of a catalytic amount of B(C₆F₅)₃ is described.
S. Chandrasekhar, G. Chandrasekhar, M. S. Reddy, P. Srihari, Org. Biomol. Chem., 2006, 4, 1650-1652.

A complex of catalytic amounts of CuH with a nonracemic JOSIPHOS or SEGPHOS ligand leads to exceedingly efficient and highly enantioselective 1,4-reductions of α,β-disubstituted enoates and lactones using PMHS as the stoichiometric reducing agent.
B. H. Lipshutz, J. M. Servesko, B. R. Taft, J. Am. Chem. Soc., 2004, 126, 8352-8353.

Catalytic amounts of copper hydride ligated by a nonracemic SEGPHOS ligand leads in situ to an extremely reactive species capable of effecting asymmetric hydrosilylations of conjugated cyclic enones with very high enantioselectivity.
B. H. Lipshutz, J. M. Servesko, T. B. Petersen, P. P. Papa, A. A. Lover, Org. Lett., 2004, 6, 1273-1275.

Various carbon-carbon double bonds in olefins and α,β-unsaturated ketones were effectively reduced to the corresponding alkanes and saturated ketones, using ammonium formate as a hydrogen transfer agent in the presence of Pd/C as catalyst in refluxing methanol.
Z. Paryzek, H. Koenig, B. Tabacka, Synthesis, 2003, 2023-2026.

Poly(ethylene glycol) (PEG) (400) has been found to be a superior solvent over ionic liquids by severalfold in promoting the hydrogenation of various functional groups using Adams' catalyst. Both the catalyst and PEG were recycled efficiently over 10 runs without loss of activity, and without substrate cross contamination.
S. Chandrasekhar, S. Y. Prakash, C. L. Rao, J. Org. Chem., 2006, 71, 2196-2199.

A microwave-assisted, palladium-catalyzed catalytic transfer hydrogenation of different homo- or heteronuclear organic compounds using formate salts as a hydrogen source was performed in ([bmim][PF₆]. Essentially pure products could be isolated in moderate to excellent yields by simple liquid-liquid extraction.
H. Berthold, T. Schotten, H. Hönig, Synthesis, 2002, 1607-1610.

The electrophilic reactivity of α,β-unsaturated amides towards weak nucleophiles such as arenes and cyclohexane is initiated either with triflic acid (CF₃SO₃H) or with excess AlCl₃. The amides generally condense readily with aromatics in the presence of AlCl₃ to give 3-arylpropionamides and related compounds in excellent yields, while some amides also undergo selective ionic hydrogenation with cyclohexane to give saturated amides.
K. Y. Koltunov, S. Walspurger, J. Sommer, Eur. J. Org. Chem., 2004, 4039-4047.

Treatment of γ-hydroxy-α,β-acetylenic esters with sodium borohydride or Red-Al gave γ-hydroxy-α,β-alkenoic esters by means of trans-selective addition of two hydrogen atoms or a hydrogen atom and an iodine atom across the triple bond.
C. T. Meta, K. Koide, Org. Lett., 2004, 6, 1785-1787.

Ruthenium complexes of rigid diphosphane ligands with large dihedral angles are highly efficient catalysts for the asymmetric hydrogenation of α,β-unsaturated carboxylic acids.
X. Cheng, Q. Zhang, J.-H. Xie, L.-X. Wang, Q.-L. Zhou, Angew. Chem., 2005, 117, 1142-1145.

A highly enantioselective reduction of α,β-unsaturated nitriles can be conducted by using a Cu(OAc)₂/josiphos complex as the catalyst under hydrosilylation conditions. The reaction provides access to valuable β-aryl-substituted chiral nitriles in good yields and with excellent enantioselectivities.
D. Lee, D. Kim, S. Yun, Angew. Chem. Int. Ed., 2006, 45, 2785-2787.

Various di- and triarylfurans were prepared in high yields from but-2-ene-1,4-diones and but-2-yne-1,4-diones using formic acid in the presence of a catalytic amount of palladium on carbon in poly(ethylene glycol)-200 as solvent under microwave irradiation.
H. S. P. Rao, S. Jothilingam, J. Org. Chem., 2003, 68, 5392-5394.

Several aryl-substituted pyrrole derivates were prepared conveniently in a microwave-assisted one pot-reaction from but-2-ene-1,4-diones and but-2-yne-1,4-diones via Pd/C-catalyzed hydrogenation of the carbon-carbon double bond/triple bond followed by amination-cyclization.
H. S. P. Rao, S. Jothilingam, H. W. Scheeren, Tetrahedron, 2004, 60, 1625-1630.