One-pot diastereoselective synthesis of tetrahydroepimino-benzo[b]azocines through sequential [3+2]-cycloaddition and Staudinger-aza-Wittig reactions

The one-pot synthesis of tetrahydro-epiminobenzo[b]azocines through a sequential 1,3-dipolar cycloaddition and intramolecular Staudinger-aza-Wittig reaction sequence is reported. This methodology provides a new and efficient approach for medium-sized and bridged nitrogen heterocyclic molecules.     

Organocatalytic asymmetric [3+2]-cycloaddition of 3-isothiocyanato oxindoles with 1,3,5-trisubstituted-hexahydro-1,3,5-triazines to access spiro-imidazolidinethione-oxindoles

An efficient asymmetric [3 + 2]-cycloaddition reaction of 3-isothiocyanato oxindoles and formaldimines in-situ generated from 1,3,5-trisubstituted-hexahydro-1,3,5-triazines with a cinchona alkaloid-derived thiourea as the catalyst has been developed. A range of biologically important spiro-imidazolidinethione-oxindoles were obtained in excellent yields with good enantioselectivities (up to 99% yield and 93% ee).     

[3+2]‐Cycloaddition for Fully Decorated Vinyl‐1,2,3‐Triazoles: Design,Synthesis and Applications

The s mall heterocyclic ring of the 1,2,3‐triazole module is one of the most widely investigated compounds in numerous applications of biological, medicinal, pharmaceutical and materially important molecules. In this regard, a large number of synthetic methodologies and approaches have already been reported to construct such a heterocyclic core structure in a selective manner. However, the vinyl‐substituted 1,2,3‐triazole moiety is another privileged segment in heterocyclic chemistry. The selective introduction of simple vinyl and functionalized vinyl groups onto the three different positions of the 1,2,3‐triazole framework can significantly improve the properties of the molecule. Accordingly, high‐yielding efficient approaches for the selective construction of vinyl‐containing 1,2,3‐triazoles becomes a promising branch of chemistry among practitioners of industry and academia. In this minireview, we have discussed recent advances in the construction of highly selective three different vinyl‐containing 1,2,3‐triazoles. In addition, representative synthetic methodologies and approaches for the corresponding three different classes of vinyl‐1,2,3‐triazoles and their applications have been described as well in this review.     

Alkoxycarbonylimines of hexafluoroacetone in reaction of [2+4]-cycloaddition

The [2+4]-cycloadditions of alkoxycarbonylimines of hexafluoroacetone to cyclopentadiene andN-nitriles have been studied. Alkoxycarbonylimines of hexafluoroacetone may be considered as both dienophiles and 1,3-heterodienes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1809–1813, September, 1995.     

Organocatalytic Formal Intramolecular [3+2]-Cycloaddition to Acquire Biologically Important Methanodibenzo[a,f]azulenes and Methanobenzo[f]azulenes

Lawsones were transformed into the functionally rich framework of methanodibenzo[a,f]azulenes and methanobenzo[f]azulenes in a single- or two-pot operation through five organocatalytic sequential reactions in very good yields with excellent selectivities. These resultant molecules are basic skeletons of important antibiotics, which highlights the value of this formal intramolecular [3+2]-cycloaddition as a key protocol.     

乙酸酐促进的[3+3]环化反应合成2-喹啉酮衍生物

2-喹啉酮结构单元广泛存在于天然产物和药物活性分子中,并且是重要的杂环合成砌块.建立了一种乙酸酐促进下,环状β-烯胺酮和丙二酸通过[3+3]环合反应构建2-喹啉酮化合物的新方法,产率为70％～87％.该方法具有原料简单易得、操作简便、路线简洁、目标化合物可修饰性强等优点.     

Catalyst-Free [3+2] Cycloaddition of Isoquinolinium/Pyridinium Ylides and Electron-Deficient Alkenes

The development of simple-to-operate methods for the preparation of indolizidine derivatives are of great importance. A mild one-pot protocol for the [3+2] cycloaddition of isoquinolinium/pyridinium ylides and electron-deficient alkenes using NaBH₃CN as reductant has been developed. The protocol has a broad substrate scope (more than 40 examples) and provides various novel hexahydroindolizidine derivatives in high yields and excellent diastereoselectivities (up to >20/1).     

Frontier-orbital analyses of ketene [2+2] cycloadditions

Twelve kinds of ketene [2+2] cycloadditions have been investigated by ab initio calculations. They are composed of four ketenes (Y–HC=C=O, Y=H, NH₂, Cl, and CN) and three isoelectronic ketenophiles (ethylene, methylenimine, and formaldehyde). All the transition state geometries obtained here are not different significantly, but the extent of formation of two covalent bonds differs appreciably. The difference is attributable to the degree of the charge transfer interactions. One is the interaction from the π orbital and/or the lone pair orbital of a ketenophile to the LUMO of a ketene (dominant charge transfer, CT1). The other is that from the HOMO of the ketene to the π* orbital of the ketenophile (second dominant charge transfer, ct1). CT1 contributes to the formation of only one covalent bond, and ct1 does to the formation of the other. This independent function is characteristic of ketene [2+2] cycloadditions. They are not concerned with the orbital phase. We also have examined Fukui's postulate that the deformation of particular frontier orbitals causes the reaction progress. The role has been verified both by configuration analyses along the intrinsic reaction coordinate of the ketene-ethylene reaction and by the examination of distortions of frontier-orbital shapes along the low-frequency vibrational modes. Received: 25 June 1998 / Accepted: 28 August 1998 / Published online: 11 November 1998     

Reactivity of allenoates toward aziridines: [3+2] and formal [3+2] cycloadditions

The reactivity of buta-2,3-dienoates toward aziridines is reported. Allenoates react as 2π-component in the [3+2] cycloaddition with the azomethine ylide generated from cis-1-benzyl-2-benzoyl-3-phenylaziridine affording 4-methylenepyrrolidines in a site-, regio-, and stereoselective fashion. Under conventional thermolysis, cis- and trans-2-benzoyl-1-cyclohexyl-3-phenylaziridines showed a different reactivity. These aziridines participate in formal [3+2] cycloadditions with allenes via C-N bond cleavage of the three-membered ring leading to functionalized pyrroles.     

Visible light induced intermolecular [2+2]-cycloaddition reactions of 3-ylideneoxindoles through energy transfer pathway

A highly diastereoselective and regioselective [2+2]-cycloaddition reaction of 3-ylideneoxindoles has been accomplished using visible light photocatalysis. This visible light photocatalytic protocol allows an expedient access to diversely functionalized and structurally constrained oxindole derivatives containing two spirocycles and four stereogenic centers, including two all-carbon quaternary centers.     

Ring opening [3+2] cyclization of azaoxyallyl cations with benzo[d]isoxazoles: Efficient access to 2-hydroxyaryloxazolines

A selective ring-opening [3+2] cyclization reaction of benzo[d]isoxazoles with 2-bromo-propanamides has been developed.The azaoxyallyl cation intermediates are employed as C^O 3-atom synthon to build oxa-heterocycles via the selectivity of suitable cyclization partners.This transformation provides rapid access to highly functionalized 2-hydroxyaryl-oxazolines under mild conditions and excellent regioselectivity.     

Stereoselective Insertion of Benzynes into Lawsones: Synthesis of Biologically Important Benzannulated Bicyclo[3.3.0]octanes

An ideal stereoselective insertion of in situ generated benzynes into lawsones through domino formal [2+2]-cycloaddition followed by rearrangement is disclosed. The reaction allowed for the preparation of biologically important benzannulated bicyclo[3.3.0]octanes in good yields and with excellent selectivities by using simple substrates and conditions.     

Synthesis and unusual [2+2]-cycloaddition reactions of ethyl 4-chloro-2-oxobut-3-ynoate with unactivated alkenes

The highly activated acetylenes, ethyl 4-chloro-2-oxobut-3-ynoate and ethyl 4-bromo-2-oxobut-3-ynoate, were prepared from readily available bis(trimethylstannyl)acetylene in two steps with high overall yield. An unusual ability of the former to furnish [2+2]-cycloadducts with 1,1-disubstituted alkenes in the absence of irradiation and catalysts was discovered. The cycloaddition of ethyl 4-chloro-2-oxobut-3-ynoate to the 1,2-disubstituted alkenes was shown to be effectively catalyzed with stannic chloride.     

Synthesis of benzyl halide derivatives of spirohydantoins via [2+2+2] cyclotrimerization reaction

Generally, synthesis of hydantoin derivatives involve use of carbonyl compounds which in turn require multistep synthesis. Here, we report a new approach to assemble spirohydantoins via [2+2+2] cyclotrimerization reaction using commercially available, inexpensive hydantoin as a starting material.     

过渡金属催化[2+2+2]环加成反应合成吡啶衍生物

环加成反应可以一步同时构建多个化学键,是目前国内外研究最为活跃的领域之一。相比于传统方法,过渡金属催化的[2+2+2]环加成反应是合成吡啶衍生物的有效手段。本文从反应机理、非手性吡啶化合物合成和手性吡啶化合物合成三个方面阐述了近年来吡啶衍生物的研究情况,涉及Co、Rh、Ru、Fe、Ni、Ti等金属催化体系。     

Synthesis of substituted imidazolines via [3+2]-cycloaddition of aziridines with nitriles

An efficient synthesis of 2,4-disubstituted 1H-imidazolines from aziridines and nitriles in the presence of BF₃-Et₂O or triethyloxonium tetrafluoroborate has been described. The reaction proceeds via a [3+2]-cycloaddition reaction. Most of the nitriles successfully underwent cycloaddition reactions with aziridines even at room temperature in a very short time.     

Diastereo- and enantioselective palladium-catalyzed dearomative [4+2] cycloaddition of 3-nitroindoles

A Pd-catalyzed asymmetric decarboxylative [4+2] cycloaddition of 3-nitroindoles and vinyl benzoxazinanones is developed through a dearomatization approach. The reaction provides an efficient protocol for constructing a series of chiral tetrahydro-5H-indolo[2,3-b]quinolines in high yields and with excellent diastereo- and enantioselectivities.     

Synthesis of ethyl 4-chloro-2-oxobut-3-ynoate and its addition to alkyl vinyl ethers

Ethyl 4-chloro-2-oxobut-3-ynoate has been synthesized for the first time and its addition to alkyl vinyl ethers of various structures has been studied. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1537–1539, July, 2008.     

N‐Heterocyclic Carbene‐Catalyzed [2+2+2] Annulation of Allenoates with Trifluoromethylketones

In contrast with the reported phosphine‐ and DABCO‐catalyzed [3+2] and [2+2] annulation of allenoates with trifluoromethylketone, the [2+2+2] annulation of allenoates and two molecules of trifluoromethylketone was found under the condition of N‐heterocyclic carbene catalysis.