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1.
1,3-Dipolar cycloaddition reactions are important synthetic manipulations allowing the construction of five-membered heterocycles. In this article, we report the cycloaddition of phosphonyl nitrile oxides with vinylphosphonate and phosphaalkyne to form the unexpected 2:1 cycloaddition product with excellent levels of regiocontrol product. The structures of title compounds were confirmed by 1H NMR, 31P NMR, MS, and IR. The mechanism of the cycloaddition was explored using the density functional theory (DFT) method.  相似文献   

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The field of strain-driven, radical formal cycloadditions is experiencing a surge in activity motivated by a renaissance in free radical chemistry and growing demand for sp3-rich ring systems. The former has been driven in large part by the rise of photoredox catalysis, and the latter by adoption of the “Escape from Flatland” concept in medicinal chemistry. In the years since these broader trends emerged, dozens of formal cycloadditions, including catalytic, asymmetric variants, have been developed that operate via radical mechanisms. While cyclopropanes have been studied most extensively, a variety of strained ring systems are amenable to the design of analogous reactions. Many of these processes generate lucrative, functionally decorated sp3-rich ring systems that are difficult to access by other means. Herein, we summarize recent efforts in this area and analyze the state of the field.  相似文献   

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Catalytic asymmetric cycloadditions of ambident Pd‐containing dipolar species with nucleophilic dipolarophiles, namely, inverse‐electron‐demand cycloadditions, are challenging and underdeveloped. Possibly, the inherent linear selectivity of Pd‐catalyzed intermolecular allylations and the lack of efficient chiral ligands are responsible for this limitation. Herein, two cycloadditions of such intermediates with deconjugated butenolides and azlactones were accomplished by using a novel chiral hybrid P,S‐ligand and hydrogen bonding. By doing so, highly functionalized, optically active dihydroquinol‐2‐ones were produced with generally high reaction efficiencies and selectivities. Preliminary DFT calculations were performed to explain the high enantio‐ and diastereoselectivities.  相似文献   

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Numerous examples of intramolecular cycloaddition of 1,3-dienes, nitrones, and azomethine imines attest the preparative value of this variant for regioselective and stereoselective synthesis of annelated and bridged ring systems. The common features, differences, and limitations of these types of reaction are systematically reviewed.  相似文献   

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The concise total syntheses of (?)‐indoxamycins A and B is reported. The chemistry features a seven‐step preparation of a highly congested [5.5.6] tricyclic advanced common intermediate from a readily available R‐carvone derivative. Key steps involve a Pauson–Khand reaction for the rapid construction of a basic scaffold bearing a quaternary carbon, a copper‐catalyzed Michael addition for the introduction of another adjacent all‐carbon quaternary stereocenter, and a tandem retro‐oxa‐Michael addition/1,2‐addition/oxa‐Michael addition for the installation of a trisubstituted olefin side chain. This synthetic strategy allows for easy access to both enantiomers of this family of natural products and their analogues from cost‐effective starting material through straightforward chemical transformations.  相似文献   

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A practical synthesis of (−)‐englerin A was accomplished in 17 steps and 11 % global yield from commercially available achiral precursors. The key step consists of a platinum‐catalyzed [4C+3C] allenediene cycloaddition that directly delivers the trans‐fused guaiane skeleton with complete diastereoselectivity. The high enantioselectivity (99 % ee) stems from an asymmetric ruthenium‐catalyzed transfer hydrogenation of a readily assembled diene–ynone. The synthesis also features a highly stereoselective oxygenation, and a late‐stage cuprate alkylation that enables the preparation of previously inaccessible structural analogues.  相似文献   

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2-Aminoallyl cations are versatile 1,3-dipoles that could potentially be used for diverse (3+n) cycloaddition reactions. Despite some preliminary studies, the asymmetric catalytic transformation of these species is still underdeveloped. We herein report a binuclear copper-catalyzed generation of 2-aminoallyl cations from ethynyl methylene cyclic carbamates and their enantioselective (3+2) cycloaddition reaction with indoles to construct chiral pyrroloindolines. This transformation features a novel C1,N-dipolar reactivity for 2-aminoallyl cations.  相似文献   

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6‐Methylenebicyclo[3.2.1]oct‐1‐en‐3‐one, a twisted and highly reactive enone, was prepared for the first time by elimination of its bromide precursor. Its reactions as a dienophile with several dienes in Diels–Alder reactions proceeded smoothly to provide tricyclic and tetracyclic adducts, which allowed short syntheses (10–11 steps) of four kurane diterpenoids including 11β‐hydroxy‐16‐kaurene, 11α‐hydroxy‐16‐kaurene, liangshanin G, and gesneroidin B.  相似文献   

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1,4‐Di(isopropyl)‐1,4‐diazabutadiene as a Reagent for the Trapping of Monomeric Fragments of the Tetragalliumcluster Ga4[C(SiMe3)3]4 – Formation of an Unsaturated GaN2C2 Heterocycle and an Oxidation Product Containing a Ga‐O‐O‐Ga Group The tetrahedral tetragallium cluster Ga4[C(SiMe3)3]4 ( 1 ) dissociates upon dissolution to yield the monomeric fragments Ga‐R [R = C(SiMe3)3]. These monomers could be trapped now by the treatment of their solutions with 1,4‐di(isopropyl)‐1,4‐diazabutadiene. The product of the cycloaddition reaction ( 2 ) possesses a five‐membered GaN2C2 heterocycle with a coordinatively unsaturated gallium atom and an endocyclic C=C double bond. 2 is rather sensitive towards oxidation by traces of air. The contact with oxygen yielded a digallium peroxide [(C2N2iPr2)RGa‐O‐O‐GaR(C2N2iPr2)] ( 3 ) which was isolated in a very low yield only and which has a gallium atom attached to each oxygen atom of the inner peroxo group. Both chelating ligands of 3 possess an unpaired electron.  相似文献   

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A new class of m-hydroxybenzyl alcohols has been designed as competent three-carbon building blocks and achieved their application in 2-indolylmethanol-involved regioselective (3 + 3) cycloadditions under the catalysis of Brønsted acids. By this appoach, a series of indole-fused six-membered cycloadducts have been synthesized in overall good yields (up to 98%) with excellent regioselectivity (all >95: 5 rr), thus affording a powerful method for the construction of indole-fused six-membered rings. Moreover, a catalytic asymmetric version of this (3 + 3) cycloaddition has been preliminarily investigated, which revealed the potential of the reaction for constructing chiral indole-fused six-membered rings in an enantioselective manner. This work not only has accomplished the first design of m-hydroxybenzyl alcohols as competent reactants, but also represents the first application of m-hydroxybenzyl alcohols as three-carbon building blocks in cycloadditions. In addition, this work provides a good example for regioselective and C3-nucleophilic (3 + 3) cycloadditions of 2-indolylmethanols, which will substantially enrich the chemistry of 2-indolylmethanols.  相似文献   

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The first peri‐ and stereoselective [10+4] cycloaddition between catalytically generated amino isobenzofulvenes and electron‐deficient dienes is described. The highly stereoselective catalytic [10+4] cycloaddition exhibits a broad scope with high yields, reflecting a robust higher‐order cycloaddition. Experimental and computational investigations support a kinetic distribution of intermediate rotamers dictating the enantioselectivity, which relies heavily on additive effects.  相似文献   

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