Wang, X. Chen, L. Chen, Z. Zhan, Org. Sniady, K. Wheeler, R. Dembinski, Org. Zinc chloride-catalyzed 5- endo-dig cycloisomerization of 1,4-di- and 1,2,4-trisubstituted butynones in dichloromethane at room temperature provides 2,5-di- and 2,3,5-trisubstituted furans in high yields. Sniady, A. Durham, M. Morreale, K. Intramolecular cyclizations of 3-alkyne-1,2-diols and 1-aminoalkynols with very low catalyst loading of Ph 3 P AuCl-AgNTf 2 or Ph 3 P AuCl-AgOTf proceeded at room temperature to provide various substituted furans and pyrroles in excellent yields.
This method was also fully applicable to the conversion of 26 g of a substrate using only 0. Egi, K. Azechi, S. Akai, Org. Furans, pyrroles, and thiophenes are efficiently and conveniently prepared by gold-catalyzed dehydrative cyclizations of readily available, heteroatom-substituted propargylic alcohols. The reactions provide essentially pure aromatic heterocycles in high yields in minutes under open-flask conditions with low catalyst loadings.
Aponick, C. Li, J. Malinge, E. Marques, Org. A convenient, silver I -catalyzed reaction of alkynyl oxiranes in the presence of p -toluenesulfonic acid and methanol gives functionalized furans. Evidence supported a cascade mechanism. Blanc, K. Tenbrink, J. Weibel, P. Pale, J. A subsequent, mild and efficient cycloisomerization in the presence of InCl 3 as catalyst delivers 2,3,5-trisubstituted furans.
Kang, B. Connell, J. Highly substituted furans were conveniently synthesized by the platinum-catalyzed reaction of propargylic oxiranes. Propargylic aziridines were also reacted with the platinum catalyst to produce the corresponding substituted pyrroles in good yields. Yoshida, M. Al-Amin, K. Shishido, Synthesis , , A copper-catalyzed oxidative cyclization of aryl ketones with styrenes to furans, in which DMSO serves not only as a solvent but also as an oxidant, provides multiaryl-substituted furans from cheap and readily available starting materials.
Wu, Z. Huang, Y. Luo, D. Deng, H. Yi, J. Lee, C. Pao, J. Chen, A. Lei, Org. An efficient palladium-catalyzed direct arylation of 2-furaldehyde with aryl halides provides a range of 5-arylformylfuran derivatives in good yields under mild conditions. McClure, B. Glover, E. McSorley, A. Millar, M. Osterhout, F. Roschangar, Org. The reaction features easily available starting materials, a broad substrate scope, and good functional group tolerance. You, Z.
Zhang, Y. Tu, H. Tang, Y. Wang, D. Long, J. Zhao, J. Esteves, M. Koyioni, K. Christensen, P. Smith, T. Donohoe, Org. Diethylene glycol serves as a environmentally friendly and cheap substitute of ethyne, that releases H 2 O and alcohol as clean wastes. Yu, B. Shi, H. Peng, S. Sun, H. Chu, Y. Jiang, J. Cheng, Org. An efficient CuI-catalyzed coupling cyclization of gem -difluoroalkenes with active methylene carbonyl compounds such as 1,3-dicarbonyl compounds, acetoacetonitrile, and phenylsulfonylacetone enables the synthesis of 2,3,5-trisubstituted furans with the assistance of a base.
Very good isolated yields, and excellent functional group compatibility make this transformation a powerful tool for the synthesis of various furans. Zhang, W. Dai, W. Wu, S. Cao, Org.
Cui, X. Xu, L. Wojtas, M. Kim, X. Zhang, J. The method features an inexpensive metal catalyst, readily available substrates, high regioselectivity, and convenient operation. Li, Y. Yu, C. Zhu, W. Wu, H. These cyclization products serve as versatile 1,4-diketone surrogates, allowing facile in situ preparation of 2,3,5-trisubstituted furans, pyrroles, and thiophenes. Tan, N. Yoshikai, J. A highly efficient palladium-catalyzed cascade reaction of aryloxy-enynes with aryl halides under mild reaction conditions offers rapid access to 2,3,4-trisubstituted furans in very good yields in a regioselective manner.
Li, X. Cheng, C. Wang, Y. Shao, Y. Schmidt, C. Malakar, U. Beifuss, Org. A gold-catalyzed water-mediated carbene cascade reaction of propargyl diazoacetates provides furan products in good to high yields with broad substrate generality.
Bao, Y. Qian, H. Su, B. Wu, L. Qiu, W. Hu, X. Xu, Org. A mild, oxidative cycloisomerization of cis -enynols using a combination of a hypervalent iodine III reagent, molecular iodine, and a base offers an efficient synthesis of 2-acyl furans with diverse substitution patterns in a regioselective manner.
A mechanistic proposal for these transformations involving alkyne activation by trifluoroacetylhypoiodite generated in situ is presented. Du, H. Chen, J. Liu, Synlett , , An efficient FeCl 3 -catalyzed tandem propargylation-cycloisomerization reaction of propargylic alcohols or acetates with 1,3-dicarbonyl compounds leads to highly substituted furans. Ji, Y. Pan, S. Zhao, Z. Zhan, Synlett , , The FeCl3-catalyzed addition and cyclization of enamino esters with nitroolefins provides a rapid, straightforward, and general method for the synthesis of tetrasubstituted NH pyrroles in good yields and tolerates a wide range of functionality.
Further, an efficient KOAc-promoted addition and cyclization protocol provides substituted furans as well. Li, M. Ren, J. Li, Z. Guan, Synthesis , , 44 , Different gold catalysts effect either selective bromine migration or hydrogen shift in haloallenyl ketones, leading to the formation of 3- or 2-bromofurans, respectively. AuCl 3 -catalyzed transformations include 1,2-halogen migrations via proposed halirenium intermediates and allow for mild and efficient synthesis of various types of 3-halofurans.
Sromek, M. Rubina, V. Gevorgyan, J. The Au III catalyst is recycable. Zhou, P. Che, Org. Praveen, P. Kiruthiga, P. Perumal, Synlett , , A mild, gold-catalyzed cascade reaction provides efficient access to highly substituted furans. The substrates can be readily prepared from the corresponding enones through cyclopropanation. Zhang, H. Schmalz, Angew. This methodology enables also a selective monoprotodecarboxylation of several aromatic dicarboxylic acids.
Lu, C. Sanchez, J. Cornella, I. Larrosa, Org. Both terminal and internal alkynes take part in the reaction with good functional-group compatibility in the presence of only a small catalyst loading.
Tsuhi, K. Yamagata, Y. Ueda, E. Nakamura, Synlett , , A broad range of highly functional furans can be efficiently generated from Michael acceptors, tributylphosphine, and acyl chlorides in one step at room temperature in good yields. The reaction was proposed to proceed via intramolecular Wittig-type reactions, using phosphorus ylides as intermediates. Kao, S. Syu, Y.
Jhang, W. Li, Org. Catalytic amounts of phosphine and triethylamine enable an efficient protocol for the synthesis of highly functionalized furans via intramolecular Wittig reaction. Lee, T. Chang, J. Yu, G.
Reddy, M. Hsiao, W. Lin, Org. Cao, H. Zhan, J. Cen, J. Lin, Y. Lin, Q. Zhu, M. Fu, H. Jiang, Org. Many common functional groups are tolerated, and the products are obtained in very good yield under mild conditions. Xu, S. E-mail: jxxu mail. Polysubstituted furans were prepared in moderate to good yields from various sulfur ylides and alkyl acetylenic carboxylates. The method was extended to synthesize furancarboxylate, -2,4-dicarboxylates, and -2,3,4-tricarboxylates as well. The current method provides a direct and simple strategy in the synthesis of structurally diverse polysubstituted furans with mono to tricarboxylate groups from safe and readily available dimethylsulfonium acylmethylides and different alkyl acetylenic carboxylates.
Historically, the classical approaches such as Paal—Knorr and Feist—Benary syntheses of furan derivatives have been widely applied. Sulfur ylides sulfonium and sulfoxonium methylides have been used as universal synthetic precursors for various chemical transformations. One interesting and powerful method to construct the furan motif was designed through the precious metal gold-catalyzed addition of sulfur ylides to terminal alkynes in an inter- or intramolecular reaction.
The reactions were the electrophilic addition of metal gold-carbenes to electron-rich alkynes Scheme 1 I. The reactive intermediate sulfonium acylmethylides were trapped by acetylenic esters to yield substituted furans in an inter- or intramolecular reaction.
With the optimized reaction conditions, the reaction scope was then evaluated Table 2. Various sulfonium ylides 2 were examined in the reaction with dimethyl acetylenedicarboxylate DMAD 1a. We were pleased to find that the application of various sulfonium ylides 2 led to the corresponding furan-3,4-dicarboxylates 3 in moderate to good yields.
Various functional groups such as methyl, fluoro, chloro, bromo, trifluoromethyl, and cyano on the aryl group of the sulfur ylides 2 were well tolerated under optimized reaction conditions Table 2 , 3ab—3ah. In comparison with dimethylsulfonium monosubstituted benzoylmethylides 2a—2i , the sulfur ylide with more substituted on the aryl group was tested as well. To extend the application of the synthetic method, several alkyl propynoates were attempted to prepare alkyl 2-substituted furancarboxlyates Table 2.
Gratifyingly, ethyl 4,4,4-trifluorobutynoate 1c was also successful for the synthesis of the corresponding trifluoromethylated furancarboxylate derivatives. Further extension of the synthetic strategy in the preparation of trialkyl furan-2,3,4-tricarboxylates was performed Table 2. Finally, the synthetic strategy was tested in the preparation of dialkyl furan-2,4-dicarboxylates as well Table 2.
However, under our optimal conditions, only 4-ethyl 2-methyl 5-methylfuran-2,4-dicarboxylate 3en was obtained regiospecifically in DMSO as solvent. The results revealed that solvent and temperature played important effects on the reaction pathways, resulting in regioselective formation of different furan derivatives. The exact reason for the selective control is not clear now possible it is attributed the stability of intermediates in different solvents during reaction.
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