Synthesis of 1,2-diketones
A highly efficient and mild procedure for the oxidation of different types of alcohols uses TEMPO as catalyst, iodobenzene dichloride as stoichiometric oxidant, and pyridine as base. Oxidation of 1,2-diols gives α-hydroxy ketones or α-diketones depending on the amount of oxidant used. High yielding procedures for the preparation of iodoarene dichlorides have been developed.
X.-F. Zhao, C. Zhang, Synthesis, 2007, 551-557.
Aerobic oxidation of deoxybenzoins is efficiently catalyzed by 1,4-diazabicyclo[2.2.2]octane (DABCO) with air as the sole oxidant to give the corresponding benzils in excellent yields. The process has been successfully extended to a one-pot synthesis of quinoxalines from benzyl ketones and aromatic 1,2-diamines.
C. Qi, H. Jiang, L. Huang, Z. Chen, H. Chen, Synthesis, 2011, 387-396.
A series of α-diketones were readily prepared by the nitroxyl-radical-catalyzed oxidation of silyl enol ethers using magnesium monoperoxyphthalate hexahydrate (MMPP • 6 H2O) as the co-oxidant.
M. Hayashi, M. Shibuya, Y. Iwabuchi, Synlett, 2012, 23, 1025-1030.
Natural sunlight and air enable an efficient oxidation of α-aryl halogen derivatives to the corresponding α-aryl carbonyl compounds at room temperature through the combination of photocatalysis and organocatalysis. A plausible mechanism was proposed on the basis of the mechanistic studies.
Y. Su, L. Zhang, N. Jiao, Org. Lett., 2011, 13, 2168-2171.
A ruthenium-catalyzed oxidation of alkenes allows an efficient route to α-diketones using TBHP as an oxidant, is highly functional group tolerant and practically convenient, requires no additional ligand, and operates under mild conditions with short reaction times. Based upon experimental observations, a plausible mechanism is proposed.
S. Chen, Z. Liu, E. Shi, L. Chen, W. Wei, H. Li, Y. Cheng, X. Wan, Org. Lett., 2011, 13, 2274-2277.
A Wacker-type oxidation of alkynes catalyzed by PdBr2 and CuBr2 allows an efficient access to 1,2-diketones using molecular oxygen. Under optimized conditions, various alkynes give 1,2-diketones in good yield. The mechanism of this reaction was preliminarily investigated by control experiments.
W. Ren, Y. Xia, S.-J. Ji, Y. Zhang, X. Wan, J. Zhao, Org. Lett., 2009, 11, 1841-1844.
The combination of potassium persulfate and ambient air enables a catalyst- and transition-metal-free oxidation of various internal alkynes to the corresponding 1,2-diketones in very good yields. Mechanistic studies indicate a radical process with both the persulfate salt and molecular oxygen as source of the incorporated oxygen atoms.
D. Shen, H. Wang, Y. Zheng, X. Zhu, P. Gong, B. Wang, J. You. Y. Zhao, M. Chao, J. Org. Chem., 2021, 86, 5354-5361.
2,3-Dichloropyridine N-oxide as oxygen transfer reagent enables gold(I)-catalyzed oxidation of alkynes to 1,2-dicarbonyls in the absence of any acid additives and under mild conditions. The developed strategy is also effective for ynamides, alkynyl ethers/thioethers, and substrates bearing highly acid-sensitive groups. A one-pot heterocyclization provides six-membered azaheterocycles.
A. Yu. Dubovtsev, N. V. Shcherbakov, D. V. Dar'in, V. Yu. Kukushkin, J. Org. Chem., 2020, 85, 745-757.
The cheap and readily available organic dye eosin Y as photocatalyst enables the oxidation of alkynes using air as the oxidant under metal-free conditions upon irradiation with blue light to provide dicarbonylation products in good yields. Some oxidation-sensitive groups, such as formyl and a carbon-carbon double bond, were tolerated under the reaction conditions.
X. Liu, T. Cong, P. Liu, P. Sun, J. Org. Chem., 2016, 81, 7256-7261.
A concerted metallophotoredox catalysis enables an efficient decarboxylative functionalization of α,β-unsaturated carboxylic acids with aryl iodides in the presence of perylene bisimide dye to afford 1,2-diketones.
S. Chand, A. K. Pandey, R. Singh, K. N. Singh, J. Org. Chem., 2021, 86, 6343-6350.
Benzil derivatives such as diaryl 1,2-diketones are synthesized via a direct copper-catalyzed decarboxylative coupling reaction of aryl propiolic acids with aryl iodides followed by an oxidation. The reaction shows good functional group tolerance toward ester, aldehyde, cyano, and nitro groups. In addition, symmetrical diaryl 1,2-diketones are obtained from aryl iodides and propiolic acid in the presence of palladium and copper catalysts.
H. Min, T. Palani, K. Park, J. Hwang, S. Lee, J. Org. Chem., 2014, 79, 6279-6285.
The combination of electrochemical and organoselenium-catalyzed processes enables an unprecedented synthesis of α-keto acetals from readily available terminal alkynes and alcohols. The desired products are obtained in a single operation at room temperature in the absence of basic or metallic additives.
D. Ding, L. Xu, Y. Wei, J. Org. Chem., 2022, 87, 4912-4917.
A combination of copper powder and Selectfluor generates a cationic copper species that efficiently catalyze the formation of 1,2-diketones from alkynes under mild conditions with water and dioxygen as inexpensive and environmentally benign sources of oxygen.
W. Zhang, J. Zhang, Y. Liu, Z. Xu, Synlett, 2013, 24, 2709-2714.
Oxidation of alkynes using ammonium persulfate and diphenyl diselenide as catalyst in aqueous media leads to 1,2-unprotected dicarbonyl derivatives or to hemiacetals starting from terminal alkynes.
S. Santoro, B. Battistelli, B. Gjoka, C.-w. S. Si, L. Testaferri, M. Tiecco, C. Santi, Synlett, 2010, 1402-1406.
Oxidation of alkynes to α-dicarbonyl derivatives through a convenient one-pot procedure via a Brønsted acid-promoted "hydration" and a DMSO-based oxidation sequence has been achieved in high yields.
Z. Wan, C. D. Jones, D. Mitchell, J. Y. Pu, T. Y. Zhang, J. Org. Chem., 2006, 71, 826-828.
1,3-Diols undergo smooth oxidative cleavage of the C-C bond in the presence of 2-iodoxybenzoic acid (IBX) affording 1,2-diketones in excellent yields under mild conditions.
J. S. Yadav, S. K. Biswas, R. Srinivas, Synthesis, 2006, 4237-4241.
An efficient and practical method enables the synthesis of unsymmetric benzils from readily available β-ketoaldehydes via oxidation by sodium hypochlorite, decarboxylation, and chlorination with Cl2 generated from sodium hypochlorite. Various unsymmetric 1,2-diaryldiketones bearing functional groups have been obtained in very good yields under mild reaction conditions.
L. Ruan, M. Shi, N. Li, X. Ding, F. Yang, J. Tang, Org. Lett., 2014, 16, 733-735.
A Selectfluor-mediated reaction of α,β-epoxy ketones provides 1,2-diketones in good yields under transition-metal-free oxidative conditions via a ring-opening/benzoyl rearrangement/C-C bond cleavage sequence.
H. Wang, S. Ren, J. Zhang, W. Zhang, Y. Liu, J. Org. Chem., 2015, 80, 6856-6863.
Chalcone epoxides form α,α-dimethoxyacetophenones on heating with iodine in methanol through C-C bond cleavage followed by acetalization of the formyl group. The process occurs through ring opening of the chalcone epoxide by methanol to form β-methoxy alcohol, cleavage of the C-C bond in the latter to form α-ketoaldehyde, and acetalization of the formyl group to give the product.
B. G. Jadhav, S. D. Samant, Synlett, 2014, 25, 1591-1595.
A direct metal-free α-hydroxylation of α-unsubstituted β-oxoesters and β-oxoamides using m-chloroperbenzoic acid as the oxidant enables straightforward metal-free access to important α-hydroxy-β-dicarbonyl moieties under mild reaction conditions. Furthermore, the hydroxylated products can readily be converted into vicinal tricarbonyl compounds, which are useful synthetic precursors.
H. Asahara, N. Nishiwaki, J. Org. Chem., 2014, 79, 11735-11739.
An aerobic decomposition of 1,3-diaryl-2-diazo-1,3-diketones to 1,2-diaryl-1,2-diketones (benzils) can be catalyzed by a few dirhodium carboxylates (5 mol %) under a balloon pressure of oxygen at ambient temperatures. An oxygen atom from O2 is shown to be incorporated into the product accompanied by the extrusion of a carbonyl unit from the starting materials.
J.-L. Zhu, Y.-T. Tsai, J. Org. Chem., 2021, 86, 813-828.
An efficient gold(I)-catalyzed oxidation of COR2-functionalized internal alkynes provides α,β-diketoesters, 1,2,3-triketones, and α,β-diketoamides in good yields under mild conditions in the presence of 2,6-dichloropyridine N-oxide. The utility of these compounds was demonstrated by facile one-pot syntheses of azaheterocycles.
A. Y. Dubovtsev, D. V. Dar'in, V. Y. Kukushkin, Org. Lett., 2019, 21, 4116-4119.