Pd-catalyzed sequential reactions via allene intermediate for the synthesis of polycyclic frameworks containing 2,3-dihydrofuran units.
TL;DR: A stepwise process involving Sonogashira coupling, propargyl allenyl isomerization, and consecutive [4 + 2] cyclization has been realized, leading to an efficient synthesis of polycyclic compounds containing a 2,3-dihydrofuran unit.
About: This article is published in Organic Letters.The article was published on 2008-07-10. It has received 38 citations till now. The article focuses on the topics: Sonogashira coupling & Allene.
Citations
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TL;DR: A phosphine-catalyzed highly diastereoselective synthesis of tetrasubstituted 2,3-dihydrofurans, which are subunits of a range of biologically active compounds via [4+1] annulations of Morita–Baylis–Hillman carbonates with activated enones is reported.
Abstract: Nucleophilic phosphines are known to be useful mild catalysts for the synthesis of cyclic and heterocyclic compounds. Generally, tertiary-phosphine-mediated annulations are triggered by nucleophilic addition of phosphines to activated compounds. The resultant zwitterionic intermediates can react with various electrophiles such as aldehydes, imines, and activated polarized C=C bonds to furnish cyclic compounds. Herein, we report a phosphine-catalyzed highly diastereoselective synthesis of tetrasubstituted 2,3-dihydrofurans, which are subunits of a range of biologically active compounds (e.g., aflatoxin B1 and clerodin), [4] via [4+1] annulations of Morita–Baylis–Hillman carbonates with activated enones. In these annulations, Morita–Baylis– Hillman carbonates act as the one-carbon unit, which is distinguished from the modified allylic compounds reported by Lu et al. as the three-carbon units, such as in [3+2], [3+3], [3+4], and [3+6] annulation reactions. In recent years, Morita–Baylis–Hillman adducts have been illustrated as suitable starting materials for the synthesis of a variety of multifunctional compounds. During our study of the new chemistry of electron-deficient enynes, we became interested in the annulation between Morita– Baylis–Hillman carbonate 1a and conjugated yne-enone 2a. We were pleased to find that the reaction proceeded smoothly in toluene at room temperature under catalysis with 10 mol% PPh3, leading to a [4+1] adduct, 2,3-dihydrofuran 3a, in 72% yield of isolated product with 20:1 diastereoselectivity (Table 1, entry 1). The structure of 3a was established by X-ray crystallography analysis of the analogous product 3f (R=p-BrC6H4; Figure 1). [7] To improve the yield of 3a, various solvents and tertiary phosphines were tested and the results are summarized in Table 1. A higher product yield was obtained when the reaction was performed in CH2Cl2, while the selectivity was slightly decreased (Table 1, entry 2). Good yields with high selectivity were also obtained in DCE, Et2O, and 1,4-dioxane, albeit the reactions require a longer time to go to completion (Table 1, en-
105 citations
TL;DR: A review of palladium-catalyzed transformation of allenes can be found in this article, with a focus on transition metal-based reactions of allene π-systems.
Abstract: The three carbon atoms of allene moieties allow unique transformations and rapid generation of complexity. Not surprisingly, allenes became extremely versatile building blocks in organic synthesis. Transition-metal-catalyzed reactions of these cumulene π-systems have been particularly successful, and many applications in the synthesis of complex products have been reported. This review summarizes the palladium-catalyzed transformation of allenes published during the last decade. Many of the examples presented are impressive multicomponent processes or cascade reactions involving two or more steps leading to molecular complexity in simple one-pot operations. Consequently, several reactions have been developed with the goal of delivering new synthetic routes to natural products.
105 citations
TL;DR: The applications of nitroalkenes in the synthesis of three to five-membered O, N and S-heterocycles, including natural products are investigated in this paper.
Abstract: The applications of nitroalkenes in the synthesis of three- to five-membered O, N and S-heterocycles, including natural products are investigated in this review. These heterocyclic compounds were synthesized from nitroalkenes with a variety of substituents at the α and β-positions and those that were part of common and medium rings via a wide variety of reactions such as Michael addition reactions, epoxidation, [3 + 2] cycloaddition and many cascade/domino/tandem reactions. In addition, the potential of nitroalkenes to take part in multi-component and cascade reactions, particularly, in diastereo- and enantioselective versions is reviewed. The high reactivity of nitroalkenes and their potential to coordinate with the metal catalysts as well as organocatalysts signify them as efficient precursors in synthetic organic chemistry. Also, the flexibility of the nitro group in functional group manipulations has expanded the scope of the nitro group, in general, and nitroalkenes, in particular, in organic synthesis.
94 citations
TL;DR: T(m) measurements demonstrate that a covalently attached tripropargylamine side chain increases duplex stability, and molecular modeling indicates that only two out of four pyrene residues are interacting forming the exciplex while the other two do not communicate.
Abstract: The 7-tripropargylamine-7-deaza-2′-deoxyguanosine (2) containing two terminal triple bonds in the side chain was synthesized by the Sonogashira cross-coupling reaction from the corresponding 7-iodo nucleoside 1b. This was protected at the 2-amino group with an iso-butyryl residue, affording the protected intermediate 5. Then, compound 5 was converted to the 5′-O-DMT derivative 6, which on phosphitylation afforded the phosphoramidite 7. This was employed in solid-phase synthesis of a series of oligonucleotides. Tm measurements demonstrate that a covalently attached tripropargylamine side chain increases duplex stability. Both terminal triple bonds of nucleoside 2 and corresponding oligonucleotides were functionalized by the Cu(I)-mediated 1,3-dipolar cycloaddition “double click reaction” with 1-azidomethyl pyrene 3, decorating the side chain with two proximal pyrenes. While the monomeric tripropargylamine nucleoside with two proximal pyrenes (4) shows strong excimer fluorescence, the ss-oligonucleotide con...
78 citations
TL;DR: A one-pot synthesis of substituted dihydrofurans was developed through a Lewis base-catalyzed three-component cascade condensation between nitroalkenes, aldehydes, and 1,3-dicarbonyl compounds in good to excellent yields.
59 citations
References
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TL;DR: The power of cascade reactions in total synthesis is illustrated in the construction of complex molecules and underscore their future potential in chemical synthesis.
Abstract: The design and implementation of cascade reactions is a challenging facet of organic chemistry, yet one that can impart striking novelty, elegance, and efficiency to synthetic strategies. The application of cascade reactions to natural products synthesis represents a particularly demanding task, but the results can be both stunning and instructive. This Review highlights selected examples of cascade reactions in total synthesis, with particular emphasis on recent applications therein. The examples discussed herein illustrate the power of these processes in the construction of complex molecules and underscore their future potential in chemical synthesis.
1,762 citations
1,085 citations
TL;DR: This study illuminates the unusual phenomena and shows how understanding of the central problem to generate a 1,3-dipole from alkynoates or allenoates by interaction with various phosphines allows control of the reaction.
Abstract: The development of some new synthetic reactions derived from nucleophilic addition of phosphines to electron-deficient carbon-carbon triple bonds is described. These reactions show that the phosphine plays the role of a nucleophile as well as an excellent leaving group. The central problem is to generate a 1,3-dipole from alkynoates or allenoates (2,3-butadienoates) by interaction with various phosphines. This study illuminates the unusual phenomena and shows how this understanding allows control of the reaction.
865 citations
715 citations
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