Synthesis of ketones by derivatisation (hydration) of alkynes
A highly efficient [(NHC)AuCl]-based catalytic system allows the hydration of terminal and internal alkynes possessing any combination of alkyl and aryl substituents under acid-free conditions and at very low catalyst loadings.
N. Marion, R. S. Ramón, S. P. Nolan, J. Am. Chem. Soc., 2009, 131, 448-449.
TfOH as the catalyst and trifluoroethanol as solvent enable a mild Markovnikov-type hydration protocol applicable to various alkynes, including terminal arylalkynes, terminal nonfunctionalized aliphatic alkynes, and internal alkynes with excellent regioselectivity in very good yields. The reaction procedure offers broad functional group compatibility and uses a stoichiometric amount of water in the absence of any transition metal.
W. Liu, H. Wang, C.-J. Li, Org. Lett., 2016, 18, 2184-2187.
A simple combination of p-toluenesulfonic acid and acetic acid enables an efficient hydration of alkynes. The reaction provides ketones in good to excellent yields under mild conditionsvia stepwise process (addition and then hydrolysis).
H. Liu, Y. Wei, C. Cai, Synlett, 2016, 27, 2378-2383.
The neutral gold(I) complex [(IPr)AuCl] is a highly effective catalyst for the regioselective hydration of terminal alkynes, including aromatic alkynes and aliphatic alkynes providing methyl ketones in high yields. Furthermore, optically active alcohols could be obtained in high yields with very good enatioselectivities via one-pot sequential hydration/asymmetric transfer hydrogenation using Cp*RhCl[(R,R)-TsDPEN] as additional catalyst.
F. Li, N. Wang, L. Lu, G. Zhu, J. Org. Chem., 2015, 80, 3538-3546.
Aliphatic and aromatic terminal alkynes can be hydrated by the AuCl/MeOH catalyst system to afford the corresponding methyl ketones in good yields without any additive, ligand, or acid promoter. This methodology is simple, mild, and convenient.
A. K. Das, S. Park, S. Muthaiah, S. H. Hong, Synlett, 2015, 26, 2517-2520.
Small amounts of a water-soluble cobalt(III) porphyrin complex promote the hydration of terminal alkynes to give methyl ketones in very good yield. The reaction tolerates acid/base- or redox-sensitive functional groups such as alkyl silyl ethers; allyl ethers; trityl ethers; benzyl ethers; carboxylic esters; boronic esters; carboxamides; nitriles; and nitro, iodo, and acetal groups.
T. Tachinami, T. Nishimura, R. Ushimaru, R. Noyori, H. Naka, J. Am. Chem. Soc., 2013, 135, 50-53.
TiO2-supported nanosize gold particles catalyze the hydration of alkynes using morpholine as a basic cocatalyst. As the TiO2-Au/morpholine system is weakly basic, the reaction tolerates acid-sensitive functional groups (e.g., silyl ethers, ketals) and strongly coordinating group such as pyridine. In addition, the gold catalyst can be recycled by simple filtration and works well in flow reactors.
S. Liang, J. Jasinski, G. B. Hammond, B. Xu, Org. Lett., 2015, 17, 162-165.
A mild ruthenium(II)-catalyzed hydration of terminal alkynes in PEG-400 provides methyl ketones in high yield through Markovnikov addition of water.
P. S. Mainkar, V. Chippala, R. Chegondi, S. Chandrasekhar, Synlett, 2016, 27, 1969-1972.
Activated pyridine borane complexes (Py·BH2X) are capable of hydroborating alkenes at room temperature. An unusual hydroboration mechanism is discussed. Hydroboration of alkynes with Py·BH2I selectively affords the monoadducts. The preparation of synthetically useful potassium alkyltrifluoroborate salts is described.
J. M. Clay, E. Vedejs, J. Am. Chem. Soc., 2005, 127, 5766-5767.
A phosphorous acid promoted alkyne-aldehyde hydration-condensation enables a simple and environmentally benign synthesis of chalcones in high to excellent yields in an oil/water two-phase system.
Y. Zhou, Z. Li, X. Yang, X. Chen, M. Li, T. Chen, S.-F. Yin, Synthesis, 2016, 48, 231-237.
A catalyst comprising of Ph3PAuCl and AgSbF6 efficiently hydrolyzes terminal alkyne groups of propargyl acetates in the absence of acid promoters at ambient temperature within a short time. Effective regioselective hydration is facilitated by the neighboring carbonyl group. Synthesis of actinopolymorphol B is achieved involving hydration of the propargyl acetate as the key step.
N. Ghosh, S. Nayak, A. K. Sahoo, J. Org. Chem., 2011, 76, 500-511.
A mild, atom-economical, Au(III)-catalyzed hydration of 3-alkynoates allows a practical one-step synthesis of a wide range of γ-keto esters in good yields, through a carbonyl group participation enabled by a favored 5-endo-dig cyclization.
W. Wang, B. Xu, G. B. Hammond, J. Org. Chem., 2009, 74, 1640-1643.
Au-catalyzed hydration of haloalkynes enables an atom-economical synthesis of a wide range of α-halomethyl ketones as an alternative to conventional α-halogenation of ketones. Other outstanding features include excellent yields from both alkyl- and aryl-substituted haloalkynes and wide functional group tolerance.
L. Xie, Y. Wu, W. Yi, L. Zhu, J. Xiang, W. He, J. Org. Chem., 2013, 78, 9190-9191.
Gold-catalyzed intermolecular oxidation enables an efficient conversion of various terminal alkynes into the corresponding α-acetoxy ketones in the presence of 8-methylquinoline 1-oxide as the oxidant. The reaction probably proceeds through an α-oxo gold carbene intermolecular O-H insertion.
C. Wu, Z. Liang, D. Yan, W. He, J. Xiang, Synthesis, 2013, 45, 2605-2611.
An efficient, indirect anti-Markovnikov hydration of unsymmetrically substituted terminal and internal alkynes is based on TiCl4-catalyzed hydroamination reactions. Its application to ortho-alkynylhaloarenes, followed by a copper-catalyzed O-arylation, provides substituted benzo[b]furans.
L. Ackermann, L. T. Kaspar, J. Org. Chem., 2007, 72, 6149-6153.
Cyclopentanone as an electron pair donor proved highly efficient for the stabilization of allyl and vinyl cations in combination with a calcium-based catalyst system. The system enabled a transition-metal-free intermolecular carbohydroxylation of alkynes with allyl and propargyl alcohols.
T. Stopka, M. Niggemann, Org. Lett., 2015, 17, 1437-1440.
A ruthenium-catalyzed hydrative cyclization converts a range of 1,5-enynes bearing terminal alkyne and Michael acceptor moieties into cyclopentanone derivatives.
Y. Chen, D. M. Ho, C. Lee, J. Am. Chem. Soc., 2005, 127, 12184-12185.
An expedient and reliable method for accessing reactive α-oxo gold carbenes via gold-catalyzed intermolecular oxidation of terminal alkynes offers a safe and economical alternative to strategies based on diazo substrates. Its synthetic potential is demonstrated by expedient preparation of dihydrofuran-3-ones containing a broad range of functional groups.
L. Ye, L. Cui, G. Zhang, L. Zhang, J. Am. Chem. Soc., 2010, 132, 3258-3259.
Photoredox catalysis enables a direct oxidative addition of CF3 and H2O to alkynes to provide α-trifluoromethyl ketones via rapid enol-keto tautomerization. The reaction exhibits high functional group tolerance and regioselectivity. In addition, trifluoromethylated heterocycles of various sizes were synthesized from α-CF3-substituted diketones.
Y. R. Malpani, B. K. Biswas, H. S. Han, Y.-S. Jung, S. B. Han, Org. Lett., 2018, 20, 1693-1697.
A very rapid and efficient method enables a one-pot synthesis of α,α-dibromoalkanones and β-bromoenol alkanoates directly from alkynes using N,N-dibromo-p-toluenesulfonamide. The protocol offers ambient temperature, high regioselectivity, operational simplicity, and metal- and catalyst-free conditions.
R. Chawla, A. K. Singh, L. D. S. Yadav, Synlett, 2013, 24, 1558-1562.
Triflate salts of several transition metal catalysts greatly faciliate the conversion of alkynes to their corresponding vinyl triflates. Products are formed in high regioselectivity under mild conditions most especially using Zn(OTf)2. Internal alkynes bearing an aryl substituent afford vinyl triflates with a modest preference for the Z-isomer. A mechanism explains the unique role of silicon in this system.
M. H. Al-huniti, S. D. Lepore, Org. Lett., 2014, 16, 4154-4157.
Ruthenium complexes were successfully applied in highly regioselective Markovnikov additions of carboxylic acids to terminal alkynes, yielding valuable enol esters. Selectivity and activity could be further improved by the addition of catalytic amounts of AgOTf. A broad range of simple as well as electronically or sterically challenging substrates could be isolated in good to excellent yields with high regioselectivity and under mild reaction conditions.
J. Jeschke, C. Gäbler, H. Lang, J. Org. Chem., 2016, 81, 476-484.
A cobalt-catalyzed highly regio- and stereoselective hydro-oxycarbonylation of terminal and internal alkynes with carboxylic acids provides enol esters in high yields. A catalyst in situ generated from Co(BF4)2, a tridentate phosphine ligand, and zinc exhibits a higher reactivity than the corresponding cobalt/diphosphine complex.
J.-F. Chen, C. Li, Org. Lett., 2018, 20, 6719-6724.
A rhodium-catalyzed, selective intermolecular anti-Markovnikov addition of carboxylic acids to terminal alkynes gives valuable Z-enol esters. The catalyst system is applicable to a broad substrate scope and displays a wide functional group tolerance.
A. Lumbroso, N. R. Vautravers, B. Breit, Org. Lett., 2010, 12, 5498-5501.
PPh3AuCl/AgPF6-catalyzed hydroacyloxylation of alkynes with carboxylic acids affords the Markonikov addition products, whereas PPh3AuCl/AgOTf catalyst gives the more stable isomerized products via the Markonikov products.
B. C. Chary, S. Kim, J. Org. Chem., 2010, 75, 7928-7931.