Multicomponent Reactions (MCRs) are convergent reactions, in which three or more starting materials react to form a product, where basically all or most of the atoms contribute to the newly formed product. In an MCR, a product is assembled according to a cascade of elementary chemical reactions. Thus, there is a network of reaction equilibria, which all finally flow into an irreversible step yielding the product. The challenge is to conduct an MCR in such a way that the network of pre-equilibrated reactions channel into the main product and do not yield side products. The result is clearly dependent on the reaction conditions: solvent, temperature, catalyst, concentration, the kind of starting materials and functional groups. Such considerations are of particular importance in connection with the design and discovery of novel MCRs. (A. Dömling, Org. Chem. Highlights 2004, April 5. Link)
Multicomponent Reactions with Carbonyl Compounds
Some of the first multicomponent reactions to be reported function through derivatization of carbonyl compounds into more reactive intermediates, which can react further with a nucleophile. One example is the Mannich Reaction:
Obviously, this reaction only proceeds if one carbonyl compound reacts faster with the amine to give an imine, and the other carbonyl compound plays the role of a nucleophile. In cases where both carbonyl compounds can react as the nucleophile or lead to imines with the same reaction rate, preforming the intermediates is an alternative, giving rise to a standard multistep synthesis.
Carbonyl compounds played a crucial role in the early discovery of multicomponent reactions, as displayed by a number of name reactions:
Isocyanide-based Multicomponent Reactions
Isocyanides play a dual role as both a nucleophile and electrophile, allowing interesting multicomponent reactions to be carried out. One of the first multicomponent reactions to use isocyanides was the Passerini Reaction. The mechanism shows how the isocyanide displays ambident reactivity. The driving force is the oxidation of CII to CIV, leading to more stable compounds.
This interesting isocyanide chemistry has been rediscovered, leading to an overwhelming number of useful transformations. One of these is the Ugi Reaction:
Both the Passerini and Ugi Reactions lead to interesting peptidomimetic compounds, which are potentially bioactive. The products of these reactions can constitute interesting lead compounds for further development into more active compounds. Both reactions offer an inexpensive and rapid way to generate compound libraries. Since a wide variety of isocyanides are commercially available, an equivalently diverse spectrum of products may be obtained.
Variations in the starting compounds may also lead to totally new scaffolds, such as in the following reaction, in which levulinic acid simultaneously plays the role of a carboxylic acid and a carbonyl compound:
But how can multicomponent reactions be discovered? It's sometimes a simple matter of trial and error. Some very interesting MCRs have even been discovered by preparing libraries from 10 different starting materials. By analyzing the products of each combination (three-, four-, up to ten-component reactions), one is able to select those reactions that show a single main product. HPLC and MS are useful analytical methods, because the purity and mass of the new compounds help to decide rapidly whether a reaction might be interesting to investigate further. (L. Weber, K. Illgen, M. Almstetter, Synlett, 1999, 366-374. DOI)
Links of Interest
Organic Chemistry Highlights: Multicomponent Reactions
Reviews on Multicomponent Reactions
Books on Multicomponent Reactions
Jieping Zhu, Hugues Bienaymé
Hardcover, 468 Pages
First Edition, 2005
ISBN: 3-527-30806-7 - Wiley-VCH
A photoredox-catalyzed sulfonylation of silyl enol ethers with DABCO·(SO2)2 and thianthrenium salts provides diverse β-keto sulfones in moderate yields with good functional group compatibility. The use of a MeOH-derived methyl thianthrenium intermediate enables the synthesis of α-methylsulfonated ketones.
F.-S. He, P. Bao, Z. Zang, F. Yu, W.-P. Deng, J. Wu, Org. Lett., 2022, 24, 2955-2960.
A Ni-catalyzed carbonylation of cyclopropanols with benzyl bromides provides multisubstituted cyclopentenones in good yields under 1 atm of CO. The reaction proceeds through cascade carbonylation of benzyl bromides, followed by generation of nickel homoenolate from cyclopropanols via β-C elimination to afford 1,4-diketones, which undergoes intramolecular Aldol condensation.
L. Hou, W. Huang, X. Wu, J. Qu, Y. Chen, Org. Lett., 2022, 24, 2699-2704.
A copper-catalyzed highly anti-selective radical 1,2-alkylarylation of terminal alkynes with aryl boronic acids and alkyl bromides providesg facile access to various stereodefined trisubstituted alkenes in high yield under mild reaction conditions. The reaction exhibits high compatibility with a wide range of terminal alkynes and diverse aryl boronic acids.
J.-B. Tang, J.-Q. Bian, Y.-S. Zhang, Y.-F. Cheng, H.-T. Wen, Z.-L. Yu, Z.-L. Yu, Z.-L. Li, Q.-S. Gu, G.-Q. Chen, X.-Y. Liu, Org. Lett., 2022, 24, 2536-2540.
Dibenziodolium triflate displays high catalytic activity for the Groebke-Blackburn-Bienaymé Reaction that leads to a series of imidazopyridines. This salt can play the role of a hybrid hydrogen- and halogen-bond-donating organocatalyst, which electrophilically activates the carbonyl and imine groups.
M. V. Il'in, A. A. Sysoeva, A. S. Novikov, D. S. Bolotin, J. Org. Chem., 2022, 87, 4569-4579.
A [3+1+1+1] annulation of arylamines, arylaldehydes and dimethyl sulfoxide (DMSO) provides 3-arylquinolines in very good yields. In this annulation, arylamines provide two carbon atoms and one nitrogen atom, arylaldehydes furnish one carbon atom, and DMSO provides two nonadjacent methines (=CH-).
T. Yang, H. Li, Z. Nie, M.-d. Su, W.-p. Luo, Q. Liu, C.-C. Guo, J. Org. Chem., 2022, 87, 2797-2808.
Water mediates a greener and mild synthesis of thioamides with no input energy, additives, or catalysts. The presented protocol enables the conversion of readily available starting materials and the use of different array amines, and can easily be scaled-up.
A. Gupta, J. K. Vankar, J. P. Jadav, G. N. Gururaja, J. Org. Chem., 2022, 87, 2410-2420.
An ultrasound-promoted three-component reaction provides C3-cyanomethylated imidazo[1,2-a]pyridines under catalyst-free, oxidant-free, and mild conditions. A series of C3-cyanomethylated imidazo[1,2-a]pyridines were rapidly prepared with satisfactory yields and good functional group compatibility.
. Zhang, Y. Zhang, J. Zhang, Q. Wu, H. Yang, Synlett, 2022, 33, 264-268.
A copper-catalyzed three-component reaction of α,β-unsaturated ketoximes, paraformaldehyde, and amines provides imidazoles and dihydroimidazoles depending on the reaction conditions in good yields with a broad substrate scope.
G. Xu, C. Jia, X. Wang, H. Yan, S. Zhang, Q. Wu, N. Zhu, J. Duan, K. Guo, Org. Lett., 2022, 24, 1060-1065.
An N-heterocyclic carbene (NHC) and photo-co-catalyzed alkylacylation of olefins in the presence of a diazo ester provides 1,5-ketoesters with great atom economy and N2 as the only byproduct. Particularly, this radical process employs a traditional carbene precursor as the radical source.
B. Zhang, J.-Q. Qi, Y. Liu, Z. Li, J. Wang, Org. Lett., 2022, 24, 279-283.
Iodine catalyzes a cascade reaction between enaminones, hydrazines, and DMSO in the presence of Selectfluor to provide 1,4-disubstituted pyrazoles. DMSO plays a dual role as the C1 source and the reaction medium. In addition, the synthesis of 1,3,4-trisubstituted pyrazoles using aldehydes as alternative C1 building blocks has also been achieved.
H. Guo, L. Tian, Y. Liu, J.-P. Wan, Org. Lett., 2022, 24, 228-233.
A metal- and oxidant-free three-component desulfurization and deamination condensation of amidines, isothiocyanates, and hydrazines provides structurally diverse fully substituted 1H-1,2,4-triazol-3-amines. This [2 + 1 + 2] cyclization strategy offers mild reaction conditions, environmental friendliness, and easy gram-scale applications.
W. Guo, G. Liu, L. Deng, W. Mei, X. Zou, Y. Zhong, X. Zhuo, J. Org. Chem., 2021, 86, 17244-17248.
A three-component assembly of α-CF3 carbonyls, NaN3, and amines provides a variety of 5-amino NH-1,2,3-triazoles under transition-metal-free and open-air conditions. The method provides a general and operationally simple route to functionalized biologically important molecules. The NH-1,2,3-triazoles can be smoothly converted to N-2 alkylated 1,2,3-triazole products.
L. Lv, G. Gao, Y. Luo, K. Mao, Z. Li, J. Org. Chem., 2021, 86, 17197-17212.
A three-component coupling reaction of alcohols or thiols with N,N-dibromoarylsulfonamides and isonitrile and in the presence of K2CO3 provides both isoureas and isothioureas in very good yields. This metal-free process proceeds via carbodiimide intermediate at room temperature within a very short reaction time.
D. Mishra, P. Phukan, J. Org. Chem., 2021, 86, 17581-17593.
A three-component coupling involving arynes, CS2, and aliphatic amines enables a facile synthesis of biologically important S-aryl dithiocarbamates. This transition-metal-free and mild reaction is scalable and operates with good functional group compatibility. With 3-triflyloxybenzyne, a unique four-component coupling incorporating tetrahydrofuran was observed.
S. Bhattarcharjee, S. Deswal, N. Manoj, G. Jindal, A. T. Biju, Org. Lett., 2021, 23, 9083-9088.
A three component coupling of amines, carbon dioxide, and halides enables an efficient synthesis of carbamates in the presence of cesium carbonate and TBAI. The method offers mild reaction conditions and short reaction times and avoids N-alkylation of the amine and overalkylation of the carbamate. In addition, chiral substrates were resistant to racemization.
R. N. Salvatore, S. Il Shin, A. S. Nagle, K. W. Jung, J. Org. Chem., 2001, 66, 1035-1037.
An annulation between 2-aminobenzyl alcohols, benzaldehydes, and DMSO provides quinolines. Interestingly, introducing substituent groups to the α-position of sulfoxides resulted in the interchange of the positions between benzaldehydes and sulfoxides in the product quinolines.
T. Yang, Z.-w. Nie, M.-d. Su, H. Li, W.-p. Luo, Q. Liu, C.-C. Guo, J. Org. Chem., 2021, 86, 15232-15241.
A chiral sulfinamide phosphine ligand enables a Pd-catalyzed enantioselective three-component coupling of N-tosylhydrazones, aryl halides, and terminal alkynes under mild conditions utilizing (GF-Phos) to provide chiral diarylmethyl alkynes. This reaction features readily available starting materials, general substrate scope, high enantioselectivity, and ease of scale-up.
G. Zhao, Y. Wu, H.-H. Wu, J. Yang, J. Zhang, J. Am. Chem. Soc., 2021, 143, 17983-17988.
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