- Synthesis and Properties of Functional Twisted Tolanes
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The synthesis and optical properties of several novel fluorescent and/or phosphorescent bridged tolanes (tolanophanes) are reported and their optical and structural properties are investigated. Specifically, diiodinated and bisalkynylated tolanophanes were obtained, and characterized by spectroscopy and computational methods. They represent attractive building blocks for novel polymers and emissive solid-state materials.
- Kozhemyakin, Yury,Kretzschmar, Andreas,Kr?mer, Maximilian,Rominger, Frank,Dreuw, Andreas,Bunz, Uwe H. F.
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- Synthesis of Functionalised 3-Isochromanones by Silylcarbocyclisation/Desilylation Reactions
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A new protocol for the synthesis of 3-isochromanone derivatives based on rhodium-promoted silylcarbocyclisation reactions of ethynylbenzyl alcohol with different arylsilanes is described. The structure of the isochromanone depends upon the reaction condit
- Albano, Gianluigi,Morelli, Martina,Aronica, Laura Antonella
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- Configurationally Stabilized Analogs of M. ulcerans Exotoxins Mycolactones A and B Reveal the Importance of Side Chain Geometry for Mycolactone Virulence
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Mycolactones A/B (1a/b) are exotoxins of Mycobacterium ulcerans that are the molecular cause of Buruli ulcer. 1a/b represent a rapidly equilibrating mixture of Z/E isomers about the C4′=C5′ double bond of the C5-side chain. Here, we describe the syntheses
- Gehringer, Matthias,M?der, Patrick,Gersbach, Philipp,Pfeiffer, Bernhard,Scherr, Nicole,Dangy, Jean-Pierre,Pluschke, Gerd,Altmann, Karl-Heinz
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- Au(I)/(R)-BINOL-Ti(IV) concerted catalyzed asymmetric cascade cycloaddition reaction of arylalkynols
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An efficient catalytic asymmetric cascade cycloaddition reaction of arylalkynols with dioxopyrrolidines was developed. This reaction was achieved using Au(I) and (R)-BINOL-Ti(IV) bimetallic catalysts and exclusively delivered a series of chiral oxo-bridged bicyclic benzooxacine compounds in up to 86% yield with 96% ee as well as >33:1 dr. Meanwhile, three new σ bonds and three new stereogenic centers were formed in a one-pot process.
- Wang, Hongkai,Zeng, Tianlong,Chang, Weixing,Liu, Lingyan,Li, Jing
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p. 3573 - 3577
(2021/05/31)
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- Substituent-Controlled Divergent Cascade Cycloaddition Reactions of Chalcones and Arylalkynols: Access to Spiroketals and Oxa-Bridged Fused Heterocycles
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Herein, we report substituent-controlled divergent cascade cycloaddition reactions of chalcones and arylalkynols in the presence of PtI2. Depending on the substituent on the chalcone, either spiroketals or oxa-bridged fused heterocycles could be obtained in the ranges of 86–97% and 87–95% yields under identical reaction conditions. Control experiments were carried out to elucidate the origin of the high chemoselectivity. These provide a method for the synthesis of a diverse array of structurally complex oxygen-containing heterocycles. (Figure presented.).
- Chang, Weixing,Kong, Jingyang,Li, Jing,Liu, Lingyan,Wang, Hongkai,Zeng, Tianlong
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p. 4024 - 4032
(2021/07/12)
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- Synthesis of phthalan derivatives via a formal intramolecular 1,3-insertion of rhodium(II) azavinyl carbenes into O[sbnd]Si bond
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The first formal intramolecular 1,3-insertion into O[sbnd]Si bond of rhodium(II) azavinyl carbene have been developed, and valuable phthalan derivatives could be synthesized efficiently. In addition, various functional groups could be introduced to the pr
- Deng, Changchang,Duan, Shengguo,Jie, Yuchen,Luo, Huan,Xiang, Qiaoyi,Xu, Ze-Feng
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- Palladium-Catalyzed Synthesis of 6H-Dibenzo[c,h]chromenes and 5,6-Dihydrobenzo[c]phenanthridines: Application to the Synthesis of Dibenzo[c,h]chromene-6-ones, Benzo[c]phenanthridines, and Arnottin I
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6H-Dibenzo[c,h]chromenes and 5,6-dihydrobenzo[c]phenanthridines have been synthesized via Palladium (II)-catalyzed domino reactions of acetylenic substrates involving intramolecular trans-oxo/amino palladation onto the triple bond followed by nucleophilic
- Pramanik, Subhendu,Jash, Moumita,Mondal, Debasmita,Chowdhury, Chinmay
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p. 5223 - 5238
(2019/11/11)
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- Structural Basis for Genetic-Code Expansion with Bulky Lysine Derivatives by an Engineered Pyrrolysyl-tRNA Synthetase
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Yanagisawa et al. analyzed the Y306A/Y384F mutant of Methanosarcina mazei pyrrolysyl-tRNA synthetase (PylRS) with 17 non-natural, bulky oxycarbonyllysine derivatives for tRNAPyl aminoacylation and site-specific incorporation into proteins. Fourteen crystal structures of the amino acid-bound PylRS mutant revealed the structural bases of the binding. This information facilitates the structure-based design of novel amino acids. Pyrrolysyl-tRNA synthetase (PylRS) and tRNAPyl have been extensively used for genetic-code expansion. A Methanosarcina mazei PylRS mutant bearing the Y306A and Y384F mutations (PylRS(Y306A/Y384F)) encodes various bulky non-natural lysine derivatives by UAG. In this study, we examined how PylRS(Y306A/Y384F) recognizes many amino acids. Among 17 non-natural lysine derivatives, N?-(benzyloxycarbonyl)lysine (ZLys) and 10 ortho/meta/para-substituted ZLys derivatives were efficiently ligated to tRNAPyl and were incorporated into proteins by PylRS(Y306A/Y384F). We determined crystal structures of 14 non-natural lysine derivatives bound to the PylRS(Y306A/Y384F) catalytic fragment. The meta- and para-substituted ZLys derivatives are snugly accommodated in the productive mode. In contrast, ZLys and the unsubstituted or ortho-substituted ZLys derivatives exhibited an alternative binding mode in addition to the productive mode. PylRS(Y306A/Y384F) displayed a high aminoacylation rate for ZLys, indicating that the double-binding mode minimally affects aminoacylation. These precise substrate recognition mechanisms by PylRS(Y306A/Y384F) may facilitate the structure-based design of novel non-natural amino acids.
- Yanagisawa, Tatsuo,Kuratani, Mitsuo,Seki, Eiko,Hino, Nobumasa,Sakamoto, Kensaku,Yokoyama, Shigeyuki
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p. 936 - 13,949
(2019/07/17)
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- A new and facile approach to 1,2-dihydroisoquinolin-3(4: H)-imines by the Cu(i)-catalyzed reaction of 2-ethynylbenzyl methanesulfonates, sulfonyl azides and amines
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A new, step-economical and operationally simple access to unsubstituted 1,2-dihydroisoquinolin-3(4H)-imines by Cu-catalyzed MCRs under mild conditions is described. In addition, selective hydrolysis of imines to the corresponding 1,2-dihydroisoquinolin-3(4H)-ones under refluxed conc. HCl has also been investigated.
- Huang, Ying,Yi, Weiyin,Sun, Qihui,Zhang, Lirong,Yi, Fengping
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- Copper Promoted Regio- and Stereoselective Aminochlorination of Alkynes and Alkenes with NFSI
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A simple and rapid copper-promoted aminochlorination of unactivated alkynes and alkenes with N-fluorobenzenesulfonimide (NFSI) was developed. Two series of chloroenamines and chloroamines were obtained in good to high yields. The chlorinated enamines could be obtained in a single E configuration. This reaction involved a radical process and the CuCl2 acted as the Cl source and NFSI as the N source.
- Wang, Weilin,Liu, Lingyan,Chang, Weixing,Li, Jing
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p. 8542 - 8547
(2018/05/30)
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- The Divergent Cascade Reactions of Arylalkynols with Homopropargylic Amines or Electron-Deficient Olefins: Access to the Spiro-Isobenzofuran- b-pyrroloquinolines or Bridged-Isobenzofuran Polycycles
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Two divergent cascade reactions of arylalkynols with homopropargylic amines or electron-deficient olefins were developed to synthesize the spiro-isobenzofuran-b-pyrroloquinolines or bridged-isobenzofuran heterocycles in good yields, respectively. One reaction actually involved intramolecular 5-endo-dig hydroamination cyclization-protonation of homopropargylic amines to give cycloiminium ions and intramolecular 5-exo-dig hydroalkoxylation cyclization of arylalkynols to generate isobenzofuran with exocyclic double bond, followed by the nontypical Povarov-type reaction in the presence of PtCl2/FeCl3 cocatalysts. The other underwent intramolecular hydroalkoxylation cycloisomerization of alkynols with the subsequent normal [4 + 2] cycoaddition with dienophiles. Herein, the arylalkynols acted as both "masked" electron-rich olefins and "masked" electron-rich dienes.
- Wang, Lun,Liu, Lingyan,Chang, Weixing,Li, Jing
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p. 7799 - 7813
(2018/06/18)
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- Efficient carbon-supported heterogeneous molybdenum-dioxo catalyst for chemoselective reductive carbonyl coupling
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Reductive coupling of various carbonyl compounds to the corresponding symmetric ethers with dimethylphenylsilane is reported using a carbon-supported dioxo-molybdenum catalyst. The catalyst is air- and moisture-stable and can be easily separated from the reaction mixture for recycling. In addition, the catalyst is chemoselective, thus enabling the synthesis of functionalized ethers without requiring sacrificial ligands or protecting groups.
- Liu, Shengsi,Li, Jiaqi,Jurca, Titel,Stair, Peter C.,Lohr, Tracy L.,Marks, Tobin J.
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p. 2165 - 2169
(2017/07/22)
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- Synthesis of 5-Iodo-1,2,3,4-tetrahydropyridines by Rhodium-Catalyzed Tandem Nucleophilic Attacks Involving 1-Sulfonyl-1,2,3-triazoles and Iodides
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Sodium iodide is used for the first time as a nucleophile to trap an α-imino rhodium carbene, which triggers a tandem process involving intermolecular nucleophilic attack and intramolecular SN2 reaction. A series of 5-iodo-1,2,3,4-tetrahydropyridines are obtained in high yield, and the synthetic utility of the products is demonstrated in cross-coupling reactions and the construction of biorelated polycyclic compounds.
- Man, Zengming,Dai, Haican,Shi, Yinping,Yang, Dongdong,Li, Chuan-Ying
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p. 4962 - 4965
(2016/10/18)
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- Intramolecular C-H activation through gold(I)-catalyzed reaction of iodoalkynes
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The cycloisomerization reaction of 1-(iodoethynyl)-2-(1-methoxyalkyl)arenes and related 2-alkyl-substituted derivatives gives the corresponding 3-iodo-1-substituted-1H-indene under the catalytic influence of IPrAuNTf2 [IPr = 1,3-bis(2,6-diisopropyl)phenylimidazol-2-ylidene; NTf2 = bis(trifluoromethanesulfonyl)imidate]. The reaction takes place in 1,2-dichloroethane at 80°C, and the addition of ttbp (2,4,6-tritert-butylpyrimidine) is beneficial to accomplish this new transformation in high yield. The overall reaction implies initial assembly of an intermediate gold vinylidene upon alkyne activation by gold(I) and a 1,2-iodine-shift. Deuterium labeling and crossover experiments, the magnitude of the recorded kinetic primary isotopic effect, and the results obtained from the reaction of selected stereochemical probes strongly provide support for concerted insertion of the benzylic C-H bond into gold vinylidene as the step responsible for the formation of the new carbon-carbon bond.
- Morn-Poladura, Pablo,Rubio, Eduardo,Gonzlez, Jos M.
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p. 3052 - 3055
(2015/04/14)
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- Formation and in situ reactions of hypervalent iodonium alkynyl triflates to form cyanocarbenes
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The conversion of readily available silylalkynes, iodobenzene diacetate, and azide anions was utilized to form and react cyanocarbenes. A copper(ii)-catalyzed reaction was found to react in a different manner. Both of these methods benefit from the formation and in situ reaction of hypervalent iodonium alkynyl triflates in O-H insertion reactions. This journal is
- Dempsey Hyatt,Nasrallah, Daniel J.,Maxwell, Michael A.,Hairston, A. Christina F.,Abdalhameed, Manahil M.,Croatt, Mitchell P.
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p. 5287 - 5289
(2015/03/30)
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- Selective oxidations of activated alcohols in water at room temperature
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Allylic and benzylic alcohols can be selectively oxidized to their corresponding aldehydes or ketones in water containing nanoreactors composed of the designer surfactant TPGS-750-M. The oxidation relies on catalytic amounts of CuBr, bpy, and TEMPO, with N-methyl-imidazole; air is the stoichiometric oxidant. the Partner Organisations 2014.
- Lipshutz,Hageman,Fennewald,Linstadt,Slack,Voigtritter
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supporting information
p. 11378 - 11381
(2014/11/08)
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- Direct access to enantioenriched spiroacetals through asymmetric relay catalytic three-component reaction
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The gold(I)/chiral Br?nsted acid relay catalysis enabled a highly stereoselective three-component reaction of salicylaldehydes, anilines, and alkynols to give aromatic spiroacetals in high yields and stereoselectivities.
- Wu, Hua,He, Yu-Ping,Gong, Liu-Zhu
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p. 460 - 463
(2013/04/11)
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- [3,3]-Sigmatropic rearrangement step in the gold-catalyzed cyclization of allyl-(ortho-alkinylphenyl)methyl ethers
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The gold-catalyzed conversion of allyl-(ortho-alkynylphenyl)methyl ethers was investigated, and allylated isochromenes were obtained. An optimization of the catalysis conditions with respect to different phosphane and carbene ligands on gold, different counterions, and different solvents was conducted. Subsequently, the scope and limitations of this reaction were investigated with 21 substrates. The mechanistic studies show an allylic inversion, as supported by NMR data and an X-ray crystal structure analysis, as well as an intermolecular reaction, as determined by crossover experiments. There is no competition of protodeauration even in the presence of water. All these observations differ from other related conversions and clearly indicate product formation by a [3,3]sigmatropic rearrangement in the step forming the new C-C bond. The Golden Key: Allylic inversion and crossover experiments reveal a sigmatropic rearrangement as a key step in the gold-catalyzed intramolecular allyl transfer in ortho-alkinyl benzyl allyl ethers. Copyright
- Ackermann, Martin,Bucher, Janina,Rappold, Melissa,Graf, Katharina,Rominger, Frank,Hashmi, A. Stephen K.
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p. 1786 - 1794
(2013/09/02)
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- Regioselective synthesis and evaluation of 3-alkylidene-1, 3-dihydroisobenzofurans as potential antidepressant agents
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3-Alkylidene-1,3-dihydroisobenzofurans exhibited moderate antidepressant activity as evaluated by forced swim and tail suspension test methods. Virtual screening was carried out by docking the designed compounds into the serotonin binding sites of arabinase protein to predict the analogue binding mode of the compounds to the SSRIs. [Figure not available: see fulltext.]
- Praveen,Iyyappan,Girija,Kumar, K Suresh,Perumal
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body text
p. 451 - 462
(2012/08/07)
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- Rhodium(III)-catalyzed intramolecular annulation through C-H activation: Total synthesis of (±)-antofine, (±)-septicine, (±)-tylophorine, and rosettacin
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Annulation: The efficient synthesis of 3-hydroxyalkyl isoquinolones and 6-hydroxyalkyl 2-pyridones is enabled through the intramolecular annulation of alkyne-tethered hydroxamic esters (see scheme, Cp= pentamethylcyclopentadienyl). The reaction features high regioselectivity, broad substrate scope, and excellent functional-group tolerance, proceeds under mild reaction conditions with low catalyst loading, and obviates the need for an external oxidant.
- Xu, Xianxiu,Liu, Yu,Park, Cheol-Min
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supporting information
p. 9372 - 9376
(2012/10/29)
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- Pd(0)-catalyzed [1,5]-sigmatropic hydrogen shift of propargylic esters toward substituent naphthylamines
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A novel and convenient carboannulation method for the synthesis of highly substituted naphthylamine derivatives has been developed though a Pd(0)-catalyzed [1,5]-sigmatropic hydrogen shift and cyclization reaction of propargyl esters.
- Zhao, Shu-Chun,Shu, Xing-Zhong,Ji, Ke-Gong,Zhou, An-Xi,He, Ting,Liu, Xue-Yuan,Liang, Yong-Min
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supporting information; experimental part
p. 1941 - 1944
(2011/05/14)
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- A straightforward double intramolecular cyclization of dibenzyl dichalcogenols into a triple bond
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The intramolecular cyclizations of four types of dibenzyl chalcogenols, which contained one or two ethynyl groups, were carried out. Either the double 5-exo or 6-endo-dig mode ring closure reaction regio- and stereoselectively proceeded to give the corres
- Sashida, Haruki,Kaname, Mamoru,Nakayama, Akemi,Suzuki, Hirokazu,Minoura, Mao
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experimental part
p. 5149 - 5157
(2010/08/20)
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- A simple and mild synthesis of 1H-isochromenes and (Z)-1-alkylidene-1,3- dihydroisobenzofurans by the iodocyclization of 2-(1-alkynyl)benzylic alcohols
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(Chemical Equation Presented) A variety of iodo-substituted isochromenes, dihydroisobenzofurans, and pyranopyridines are readily prepared in good to excellent yields under mild conditions by the iodocyclization of readily available 2-(1-alkynyl)benzylic a
- Mancuso, Raffaella,Mehta, Saurabh,Gabriele, Bartolo,Salerno, Giuseppe,Jenks, William S.,Larock, Richard C.
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supporting information; experimental part
p. 897 - 901
(2010/05/02)
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- Iodine-mediated electrophilic cyclization of 2-alkynyl-1-methylene azide aromatics leading to highly substituted isoquinolines and its application to the synthesis of norchelerythrine
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The reaction of 2-alkynyl-1-methylene azide aromatics 1 with iodine and/or other iodium donors, such as the Barluenga reagent (Py2IBF 4/HBF4) and NIS, gave highly substituted cyclization products, namely, the 1,3-disubstituted 4-iodoisoquinolines 2, in good to high yields. Not only simple 2-alkynyl benzyl azides 1a-j and their substituted analogues 1k-u and 6 but also heteroaromatic analogues, including pyridine 8, pyrroles 10a-c, furane 10d, and thiophenes 10e-g, gave the corresponding isoquinoline derivatives in excellent to allowable yields. Electron-donating and electron-accepting substituents on the aromatic ring were equally tolerated, and either acidic or basic (or even neutral) reaction conditions, depending on the reactivity of the substrate, could be applied to smoothly convert the azide starting materials into the desired isoquinoline products in moderate to good yields. Limits were found only in connection with the substituent at the alkyne terminus, where electron-neutral or electron-donating substituents are clearly favored. The iodine-mediated electrophilic cyclization of 1 most probably proceeds through the iodonium ion intermediate 4 followed by nucleophilic cyclization of the azide and subsequent elimination of N2. This new methodology was successfully applied to the short synthesis of norchelerythrine.
- Fischer, Dirk,Tomeba, Hisamitsu,Pahadi, Nirmal K.,Patil, Nitin T.,Huo, Zhibao,Yamamoto, Yoshinori
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supporting information; scheme or table
p. 15720 - 15725
(2009/03/12)
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- Synthesis of 1,3,4-trisubstituted isoquinolines by iodine-mediated electrophilic cyclization of 2-alkynyl benzyl azides
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(Chemical Equation Presented) The I's have it: A series of 2-alkynyl benzyl azides have been smoothly converted into 1,3,4-trisubstituted isoquinolines in moderate to excellent yields by an iodonium-mediated synthesis (see scheme). Depending on the struct
- Fischer, Dirk,Tomeba, Hisamitsu,Pahadi, Nirmal K.,Patil, Nitin T.,Yamamoto, Yoshinori
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p. 4764 - 4766
(2008/02/10)
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- Synthesis of γ- and δ-lactones from alkynols
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The reaction of alkynyl phenyl selenides with p-toluene-sulfonic acid gives rise to a proton-induced ring-closure reaction affording γ- and δ-lactones. Georg Thieme Verlag Stuttgart.
- Tiecco, Marcello,Testaferri, Lorenzo,Temperini, Andrea,Terlizzi, Raffaella,Bagnoli, Luana,Marini, Francesca,Santi, Claudio
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p. 587 - 590
(2007/10/03)
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- Free radical-mediated vinyl amination: A mild, general pyrrolidinyl enamine synthesis
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The complete scope of free radical-mediated vinyl amination is described, using 5-exo-trig cyclizations of vinyl radicals to the nitrogen of azomethines. The focus is primarily on N,N-dialkyl enamines since their nucleophilicity renders them the most challenging enamines to synthesize using redox conditions. These studies establish several encouraging precedents for the broader application of this strategy.
- Nugent, Benjamin M.,Williams, Amie L.,Prabhakaran,Johnston, Jeffrey N.
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p. 8877 - 8888
(2007/10/03)
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- Versatile synthesis of (Z)-1-alkylidene-1,3-dihydroisobenzofurans and 1H-isochromenes by palladium-catalyzed cycloisomerization of 2-alkynylbenzyl alcohols
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An easy synthesis of (Z)-1-alkylidene-1,3-dihydroisobenzofurans and 1H-isochromenes by palladium-catalyzed cycloisomerization of readily available 2-alkynylbenzyl alcohols under neutral conditions is reported. Reactions were carried out at 70-100°C in the
- Gabriele, Bartolo,Salerno, Giuseppe,Fazio, Alessia,Pittelli, Rosina
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p. 6251 - 6259
(2007/10/03)
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- Cyclization reactions of 2-alkynylbenzyl alcohol and 2-alkynylbenzylamine derivatives promoted by tetrabutylammonium fluoride
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The regioselectivity of the cyclization reaction of 2-ethynylbenzyl alcohol and 2-ethynylbenzylamine derivatives promoted by TBAF was investigated. Six-membered ring derivatives were obtained from the compounds, which have a butyl group on the triple bond. Whereas five-membered ring products were afforded from the substrates having hydrogen or aromatic substituents on the acetylene moiety. It was also concluded that both the tetrabutylammonium cation and fluoride anion were essential for the cyclization. Thus, the actual mechanism and catalytic cycle were also suggested.
- Hiroya, Kou,Jouka, Rumi,Kameda, Mitsuyoshi,Yasuhara, Akito,Sakamoto, Takao
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p. 9697 - 9710
(2007/10/03)
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- Synthesis of biaryls using nickel-catalyzed [2+2+2] cocyclization
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Methods of synthesizing biaryls using nickel-catalyzed [2+2+2] cocyclization were developed. Two ways for the synthesis of biaryl using [2+2+2] cocyclization were investigated: one method is that biaryls synthesized from alkyne having a phenyl group and 2
- Sato, Yoshihiro,Ohashi, Kenji,Mori, Miwako
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p. 5231 - 5234
(2007/10/03)
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- 2-(iodoethenyl)benzylamines as potential probes for radical intermediates formed during monoamine oxidase catalyzed oxidations
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An attempt to trap radical intermediates during the monoamine oxidase (MAO) catalyzed oxidation of amines by intramolecular cyclization with an activated alkene that is built into the substrate was unsuccessful. (E)-2- (Iodoethenyl)benzylamine (3a) was shown to be a reversible inhibitor of MAO B, but the corresponding Z isomer (3b) was a good substrate. By GC-MS analysis, the expected radical trapping product, isoquinoline (5), was observed as one of two products in 1:1 ratio. However, NMR analysis prior to GC-MS analysis showed no evidence of isoquinoline, suggesting that the isoquinoline was generated during gas chromatography. As a model for this GC- dependent reaction, the corresponding aldehyde, (Z)-2- (iodoethenyl)benzaldehyde (14), was treated with ammonia, and the product was analyzed by GC-MS; isoquinoline was detected. Likewise, the reaction of 14 with methylamine also produced isoquinoline by GC-MS analysis (but not by NMR analysis). These results are explained by electrocyclization of the corresponding imines at the elevated temperatures in the GC (Schemes 7 and 8). Substrate 3b and aldehyde 14 were recovered when the enzyme reaction products were chromatographed, although they were not detected by GC-MS. These products could arise via hydrolytic decomposition of the corresponding imine (17, Scheme 9). GC-MS analysis of 17 produced isoquinoline and (Z)-2- (iodoethenyl)benzyl iodide (18) in a 1:1 ratio; these are the two products observed in a 1:1 ratio after incubation of MAO with 3b and apparently arise from thermally induced electrocyclization and iodide ion cleavage (Scheme 9).
- Wang, Xueqing,Silverman, Richard B.
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p. 7357 - 7363
(2007/10/03)
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- Towards a new type of aromatic diynes activation : Synthesis of a novel bicyclic enediyne
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The aromatic acyclic diynes 2 and 3 have been synthesised in order to test the feasibility of a new activation towards their cyclisation. In addition, a difference of stability between 13 and 20 during the Nozaki-Kishi cyclisation reaction occurs when the aromatic ring possesses or not an intramolecular trigger device. Thus, the aromatic bicyclic enediyne 14 is stable while 21 has not been isolated.
- Raeppel, Stéphane,Toussaint, Dominique,Suffert, Jean
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p. 537 - 539
(2007/10/03)
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- The first syntheses of 6-/10-membered ring analogs and of a 6-/11-membered ring analog of the dienediyne core of the neocarzinostatin chromophore by ring-closure according to the Nozaki-Hiyama reaction
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The Z-configurated dienediyne aldehydes 11, 13, 19, and 20 were prepared as pure isomers by Pd(0)-catalyzed C,C couplings between appropriate terminal alkynes and the bis(enol trifluoromethanesulfonate) 5 or its mono(enol trifluoromethanesulfonate) derivative 18. Irrespective whether these aldehydes contained a C≡C-H or a C≡C-SiMe3 moiety, they cyclized with low efficiency (11, 13, 19) or not at all (20) to the corresponding 6-/10-membered ring dienediynes (compounds 10, 8, 21, and 22, respectively). However, the C≡C-I analogs 6 and 26 of these aldehydes furnished the desired 6-/10-membered ring dienediynes 8 and 22 by Nozaki-Hiyama reactions; these cyclizations were complete and essentially clean conversions, provided an excess of CrCl2 and a stoichiometric amount of NiCl2 were used. However, since dienediynes 8 and 22 decompose very readily they were isolated only in 26 and 53 % yield. Similar ring-closure reactions of the iodinated alkinyl aldehydes 36a and b - which were obtained from the same mono(enol trifluoromethanesulfonate) 18 and the alkynes 32a and b, respectively, in four steps (Scheme 7) - furnished the 6-/10-membered ring dienediyne 38 (51% yield) and the 6-/11-membered ring dienediyne 39 (54% yield). They are the most stable dienediyne analogs of the neocarzinostatin chromophore which we have so far synthesized. They were oxidized to the corresponding dienediyne ketones 40 and 41 (Scheme 8). The latter compounds cycloaromatized in the presence of methyl thioglycolate and 1,4-cyclohexadiene at 35-37°C to give the tetrasubstituted benzenes 47 and 48 as the only and as the main product, respectively (Scheme 9). VCH Verlagsgesellschaft mbH, 1996.
- Eckhardt, Matthias,Brueckner, Reinhard
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p. 473 - 488
(2007/10/03)
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- An Unusual Example of a 6-Endo-Dig Addition to an Unactivated Carbon-Carbon Triple Bond
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Methyl 2-ethynyl>benzoate was prepared as an intermediate for subsequent conversion to an α-diazo ketone.Under the basic conditions used to hydrolyze the methyl ester, the neighboring hydroxyl functionality underwent reaction with the unactivated acetylenic group, producing a benzopyranyl-substituted α-diazoacetophenone.Treatment of this diazocarbonyl compound with a catalytic quantity of rhodium(II) mandelate afforded a novel dibenzocyclononenone derivative.The reaction proceeds via an initially formed oxonium ylide which rearranges further by means of a 1,2-alkyl shift.A prime factor in determining the direction of internal cyclization to the triple bond is the presence of the carbomethoxy group in the ortho position of the β-phenyl ring.Thus, in contrast with related systems which exhibit a clear preference for 5-exo-dig cyclization at the acetylenic center, the 6-endo-dig addition is the preferred pathway for the o-formyl- and o-carbomethoxy-substituted alkynyl alcohols.Careful monitoring of the reaction actually showed that the reaction proceeds by initial formation of the 5-exo-dig product followed by a novel rearrangement to the 6-endo product.
- Padwa, Albert,Krumpe, Keith E.,Weingarten, M. David
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p. 5595 - 5603
(2007/10/03)
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- Dimetallation of phenylacetylene. Synthesis of ortho-susbtituted derivatives of phenylacetylene, benzoselenophene and benzotellurophene
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Phenylacetylene can be dimetallated in two ways. o-K-C6H4-CC-Li is formed by treating phenylacetylene at -70 deg C with two equivalents of butyllithium and one equivalent of potassium tert-butoxide in a mixture of tetrahydrofuran and hexane.The dimetallation with BuLi*N,N,N',N'-tetramethylethanediamine (TMEDA) affords a mixture of about 15percent (m + p)-Li-C6H4-CCLi and 85percent o-LiC6H4-CC-Li.Ortho-K-C6H4-CC-Li can be transformed into the dilithio or di-Grignard derivatives by addition of anhydrous lithium bromide or magnesium bromide etherate.Reaction of the dilithio derivative with elemental selenium and tellurium, followed by successive addition of tert-butyl alcohol and hexamethylphosphoric triamide (HMPT), gives benzoselenophene and benzotellurophene in good yields.Regiospecific functionalization of the nucleus via dimetal derivatives succeeds in the case of alkylation, halogenation, sulfenylation and acylation (with dimethylformamide and dimethylacetamide).Trimethylchlorosilane, chloromethyl methyl ether, aldehydes and ketones do not however react regiospecifically.
- Brandsma, L.,Hommes, H.,Verkruijsse, H. D.,Jong, R. L. P. de
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p. 226 - 230
(2007/10/02)
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