Categories: C-H Bond Formation >
Reduction of Alkynes
|Related:||Synthesis of Alkenes|
An unprecedented reduction of alkynes with formic acid can selectively produce cis-, trans-alkenes and alkanes by slightly tuning the reaction conditions via the generation of an alkenylpalladium intermediate and subsequent transformation of this complex in a variety of reactions catalyzed by a combination of Brønsted acid and Pd(0) complex.
R. Shen, T. Chen, Y. Zhao, R. Qiu, Y. Zhou, S. Yin, X. Wang, M. Goto, L.-B. Han, J. Am. Chem. Soc., 2011, 133, 17037-17044.
Using small amounts of a copper catalyst, an efficient semireduction of alkynes can be accomplished with a wide range of substrates, including both internal and terminal alkynes without over-reduction. The new method has excellent chemoselectivity and tolerates nitro and aryl iodo groups. Finally, commercial availability of a catalyst precursor adds to the appeal of the new catalytic system.
A. M Whittaker, G. Lalic, Org. Lett., 2013, 15, 1112-1115.
(Ph3P)3RuCl2 is an inexpensive catalyst, that enables a chemoselective reduction of alkyne, ketones, or nitro groups in the presence of Zn/water as a stoichiometric reductant. Depending on the nature of the additive and the temperature, chemoselective reduction of a nitro group in the presence of a ketone or an alkyne was possible.
T. Schabel, C. Belger, B. Plietker, Org. Lett., 2013, 15, 2858-2861.
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.
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.
In situ generation of molecular hydrogen by addition of triethylsilane to palladium on charcoal results in rapid and efficient reduction of multiple bonds, azides, imines, and nitro groups, as well as deprotection of benzyl and allyl groups under mild, neutral conditions.
P. K. Mandal, J. S. McMurray, J. Org. Chem., 2007, 72, 6599-6601.
A generally applicable method for the introduction of gaseous hydrogen into a sealed reaction system under microwave irradiation allows the hydrogenation of various substrates in short reaction times with moderate temperatures between 80 °C and 100 °C with 50 psi of hydrogen.
G. S. Vanier, Synlett, 2007, 131-135.
The use of hydrogen micro and nanobubbles (MNBs) enables an autoclave-free, gas-liquid-solid multiphase hydrogenation of carbon-carbon unsaturated bonds, in which a high concentration of hydrogen gas is maintained in the liquid phase.
N. Mase, S. Isomura, M. Toda, N. Watanabe, Synlett, 2013, 24, 2225-2228.
In situ preparation of an active Pd/C catalyst from Pd(OAc)2 and charcoal in methanol enables a simple, highly reproducible protocol for the hydrogenation of alkenes and alkynes and for the hydrogenolysis of O-benzyl ethers. Mild reaction conditions and low catalyst loadings, as well as the absence of contamination of the product by palladium residues, make this a sustainable, useful process.
F.-X. Felpin, E. Fouquet, Chem. Eur. J., 2010, 12440-12445.
DMF/KOH is an efficient hydrogen source in the Pd(OAc)2-catalyzed transfer semihydrogenation of various functionalized internal alkynes to afford cis-alkenes in good to high yields with excellent chemo- and stereoselectivity. This catalytic process was also applied to the synthesis of analogues of combretastatin A-4.
J. Li, R. Hua, T. Liu, J. Org. Chem., 2010, 75, 2966-2970.
γ-Hydroxy-α,β-acetylenic esters are used as precursors for the preparation of γ-hydroxy-α,β-alkenoic esters by means of trans-selective additions of two hydrogen atoms or one hydrogen atom and one iodine atom across the triple bonds. These methods allow the preparation of β-substituted and α,β-disubstituted alkenoic esters in highly stereoselective manners.
C. T. Meta, K. Koide, Org. Lett., 2004, 6, 1785-1787.
The hydrosilylation of alkynes using the ruthenium catalyst [Cp*Ru(MeCN)3]PF6 gives only (Z)-trans addition products. Subsequent protodesilylation of the crude vinylsilane products by the action of cuprous iodide and TBAF provides a general trans-alkyne reduction, which is compatible with many sensitive functional groups.
B. M. Trost, Z. T. Ball, T. Joege, J. Am. Chem. Soc., 2002, 124, 7922-7923.
Indium hydride generated from readily available Et3SiH and InCl3 offers mild conditions and low toxicity, and is therefore a promising alternative to Bu3SnH.
N. Hayashi, I. Shibata, A. Baba, Org. Lett., 2004, 6, 4981-4983.
A number of alkynyl pinacolboronates were stereoselectively reduced to the cis-alkenyl pinacolboronates via hydroboration with dicyclohexylborane followed by chemoselective protodeboronation using acetic acid. Treatment with potassium hydrogen fluoride smoothly converted these to the corresponding potassium organotrifluoroborates.
G. A. Molander, N. M. Ellis, J. Org. Chem., 2008, 73, 6841-6844.