- HOMOLYTIC DISPLACEMENT AT CARBON. XI. INTRAMOLECULAR HOMOLYTIC DISPLACEMENT AS A ROUTE TO CYCLOPENTANE AND TETRAHYDROFURAN DERIVATIVES FROM HEX-5-ENYL- AND HEX-3-OXO-5-ENYLCOBALOXIMES
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5-Methylhex-5-enylcobaloxime reacts with carbon tetrachloride and with fluorotrichloromethane at 80-100 deg C to give substantially pure 1-methyl-1-(Β,Β,Β-trichloroethyl)- and 1-methyl-1-(β-fluoro-β,β-dichloroethyl)-cyclopentane.Hex-5-enylcobaloxime also gives trichloroethylcyclopentane from carbon tetrachloride, but the yield is dependent on the concentration of carbon tetrachloride.Similar cyclisation to give trichloroethyl- or fluorodichloroethyltetrahydrofuran is observed in the reactions of hex-3-oxo-5-enylcobaloxime with carbon tetrachloride and fluorotrichloromethane.However, no cyclisation was observed in the reactions of the ester, hex-2-one-3-oxo-5-enylcobaloxime, with carbon tetrachloride.These reactions are believed to take place by attack of a polyhalogenomethyl radical at the terminal unsaturated carbon of the organic ligand, followed either by an intramolecular homolytic displacement in which the carbon radical at position-5 attacks carbon-1 with displacement of cobaloxime(II), or by a halogen atom abstraction.
- Bongars, Christophe,Bougeard, Peter,Bury, Adrian,Cooksey, Christopher J.,Johnson, Michael D.,et al.
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Read Online
- Stereoselective total synthesis of diplodialide A
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Abstract: An efficient stereoselective total synthesis of Diplodialide A has been achieved from inexpensive and commercially available starting material (R)-propylene oxide. This linear synthesis utilizes Wittig reaction, alkylation of 1,3-dithiane and Yamaguchi macrolactonization as key steps. Graphic abstract: [Figure not available: see fulltext.]
- Ramakrishna, Kolluri,Sreenivasulu, Reddymasu,Rao, Mandava Venkata Basaveswara,Vidavalur, Siddaiah,Reddy, Boggu Jagan Mohan
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p. 931 - 937
(2020/10/02)
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- Fe-Catalyzed Anaerobic Mukaiyama-Type Hydration of Alkenes using Nitroarenes
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Hydration of alkenes using first row transition metals (Fe, Co, Mn) under oxygen atmosphere (Mukaiyama-type hydration) is highly practical for alkene functionalization in complex synthesis. Different hydration protocols have been developed, however, control of the stereoselectivity remains a challenge. Herein, highly diastereoselective Fe-catalyzed anaerobic Markovnikov-selective hydration of alkenes using nitroarenes as oxygenation reagents is reported. The nitro moiety is not well explored in radical chemistry and nitroarenes are known to suppress free radical processes. Our findings show the potential of cheap nitroarenes as oxygen donors in radical transformations. Secondary and tertiary alcohols were prepared with excellent Markovnikov-selectivity. The method features large functional group tolerance and is also applicable for late-stage chemical functionalization. The anaerobic protocol outperforms existing hydration methodology in terms of reaction efficiency and selectivity.
- Bhunia, Anup,Bergander, Klaus,Daniliuc, Constantin Gabriel,Studer, Armido
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supporting information
p. 8313 - 8320
(2021/03/08)
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- 1-D manganese(ii)-terpyridine coordination polymers as precatalysts for hydrofunctionalisation of carbonyl compounds
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Reductive catalysis with earth-abundant metals is currently of increasing importance and shows potential in replacing precious metal catalysis. In this work, we revealed catalytic hydroboration and hydrosilylation of ketones and aldehydes achieved by a structurally defined manganese(ii) coordination polymer (CP) as a precatalyst under mild conditions. The manganese-catalysed methodology can be applied to a range of functionalized aldehydes and ketones with turnover numbers (TON) of up to 990. Preliminary results on the regioselective catalytic hydrofunctionalization of styrenes by the Mn-CP catalyst are also presented.
- Johnson, Jahvon,Li, Sihan,Mo, Zixuan,Neary, Michelle C.,Zeng, Haisu,Zhang, Guoqi,Zheng, Shengping
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p. 2610 - 2615
(2020/03/05)
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- A Unified Synthetic Approach to Optically Pure Curvularin-Type Metabolites
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A unified and concise approach to the synthesis of nine curvularin-type metabolites and two analogues has been developed with few steps and high yields. Among them, sumalactones A-D were synthesized for the first time. The key steps in this approach inclu
- Allu, Srinivasa Rao,Banne, Sreenivas,Jiang, Jia,Qi, Na,Guo, Jian,He, Yun
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p. 7227 - 7237
(2019/06/07)
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- An alternative total synthesis of diplodialide-B
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In this paper, an enantioselective synthesis of diplodialide-B has been described. To accomplish this target, a combination of regioselective ring opening of the chiral epoxide, Jacobsen hydrolytic kinetic resolution and Yamaguchi macrolactonization were used as the key steps.
- Kalavakuntla, Chiranjeevi,Kummari, Vijaya Babu,Yadav, Jhillu Singh
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p. 3324 - 3328
(2019/11/11)
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- Total synthesis and stereochemical revision of relgro and 10′-oxorelgro
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The first asymmetric total synthesis and stereochemical assignments of 10-membered macrolactones relgro and 10′-oxorelgro are disclosed. To this end, palladium-catalyzed Stille coupling, the Mitsunobu reaction, ring-closing metathesis, EDCI promoted coupling and the Jacobsen hydrolytic kinetic resolution are used as key steps. The total synthesis followed by thorough evaluation of the optical rotation and CD spectral data led to the revision of the absolute configuration at C-6′ for both relgro and 10′-oxorelgro. Moreover, the 1H as well as 13C NMR data are reported for the first time for relgro.
- Gaddam, Janardhan,Reddy, G. Sudhakar,Marumudi, Kanakaraju,Kunwar, Ajit C.,Yadav, Jhillu S.,Mohapatra, Debendra K.
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p. 5601 - 5614
(2019/06/13)
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- Continuous Pd-Catalyzed Carbonylative Cyclization Using Iron Pentacarbonyl as a CO Source
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This work discloses a continuous flow carbonylation reaction using iron pentacarbonyl as source of CO. The described transformation using this surrogate was designed for use in commonly accessible flow equipment. Optimized conditions were applied to a sca
- Lopatka, Pavol,Markovi?, Martin,Koó?, Peter,Ley, Steven V.,Gracza, Tibor
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p. 14394 - 14406
(2019/11/11)
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- Enantioselective synthesis of (2R,13R,8Z)-2,13-diacetoxy-8-heptadecene, the major component of the sex pheromone of the pear leaf midge, Dasineura pyri
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The first enantioselective synthesis of (2R,13R,8Z)-2,13-diacetoxy-8-heptadecene 1, the major component of the sex pheromone of the pear leaf midge, Dasineura pyri, has been achieved. The key steps include the (R,R)-BINOL/Ti(OiPr)4catalyzed alkynylzinc addition to an unsaturated aldehyde, the ring-opening of the chiral epoxide with a Grignard reagent, and the partial reduction of an acetylenic diol ester to a (Z)-olefinic diol ester with hydrogen and P2-Ni.
- Zhou, Yun,Yang, Pengfei,Li, Shuoning,Wang, Lifeng,Yin, Jingwei,Zhong, Jiangchun,Dong, Yanhong,Liu, Shangzhong,Wang, Min,Bian, Qinghua
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p. 338 - 343
(2017/02/18)
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- Determination of the Absolute Configuration of Gliomasolide D through Total Syntheses of the C-17 Epimers
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The absolute configuration at C-17, the carbon bearing the distal hydroxy group of the 14-membered natural product gliomasolide D, was assigned as R by comparison of 13C NMR shifts and specific rotation values of the epimers at C-17. The first
- Seetharamsingh,Ganesh, Routholla,Reddy, D. Srinivasa
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supporting information
p. 560 - 564
(2017/03/09)
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- Iron-Catalyzed Synthesis of α-Dienyl Five- and Six-Membered N-Heterocycles
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The iron-catalyzed synthesis of α-dienyl N-heterocycles is reported. The method is cost-effective, atom-economic, and led to a range of substituted α-dienyl heterocycles in moderate to good yields and diastereoselectivities. The α-dienyl piperidines are key synthetic intermediates as demonstrated by the preparation of a panel of α-polyenyl N-heterocycles.
- Gonnard, Laurine,Guérinot, Amandine,Cossy, Janine
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supporting information
p. 6160 - 6167
(2017/11/15)
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- A concise stereoselective total synthesis of (-)-cephalosporolide D
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A concise stereoselective total synthesis of eight-membered lactone (-)-cephalosporolide D has been derived from inexpensive and commercially available starting material (S)-propylene epoxide. This concise synthesis utilizes Grignard reaction, Noyori asym
- Alluraiah, Gurrala,Sreenivasulu, Reddymasu,Sadanandam, Palle,Anitha, Kowthalam,Raju, Rudraraju Ramesh
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p. 451 - 455
(2016/02/16)
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- Stereoselective Synthesis of cis-2,5-Disubstituted Pyrrolidines via Copper-Catalyzed Cyclization of Alkenes
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An efficient methodology for the stereoselective synthesis of cis-2,5-disubstituted pyrrolidines using copper catalyst was developed. The corresponding cis-2,5-disubstituted pyrrolidines could be obtained in reasonable yields and with good stereoselectivities in the presence of 4,4′-di-tert-butyl-2,2′-bipyridine as ligand and 1-methyl-2-pyrrolidinone as solvent.
- Cai, Sai-Hu,Da, Bing-Chao,Zhou, Jia-Hui,Xu, Yun-He,Loh, Teck-Peng
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supporting information
p. 1076 - 1080
(2016/11/25)
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- Total synthesis of the Z -isomers of the proposed and revised structures of aspergillide B via an iodocyclization and ring-closing metathesis strategy
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The synthesis of Z-isomers of both the proposed and revised structures of aspergillide B is described. A divergent route is employed that involves kinetically controlled ring-closing metathesis for the construction of a 14-membered macrocyclic ring, ester formation under Yamaguchi conditions, a Wacker-type oxidative cyclization for creation of the C4 stereogenic center and a previously reported diastereoselective isomerization-iodocyclization strategy for the construction of the 2,6-trans-disubstituted tetrahydropyran subunit. Georg Thieme Verlag Stuttgart, New York.
- Pradhan, Tapas R.,Das, Pragna P.,Mohapatra, Debendra K.
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p. 1177 - 1184
(2014/05/20)
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- Total synthesis of nominal gobienine A
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The lichen-derived glycoconjugate gobienine A is structurally more complex than most glycolipids isolated from higher plants by virtue of the all-cis substituted γ-lactone substructure embedded into its macrocyclic frame. A concise entry into this very epimerization-prone and hence challenging structural motif is presented, which relies on an enantioselective cyanohydrin formation, an intramolecular Blaise reaction, a palladium-catalyzed alkoxycarbonylation, and a diastereoselective hydrogenation of the tetrasubstituted alkene in the resulting butenolide. This strategy, in combination with ring-closing olefin metathesis for the formation of the macrocyclic perimeter, allowed the proposed structure of gobienine A (1) to be formed in high overall yield. The recorded spectral data show that the structure originally attributed to gobienine A is incorrect and that it is not the epimerization-prone ester site on the butanolide ring that is the locus of misassignment; rather, the discrepancy must be more profound. Copyright
- Kondoh, Azusa,Arlt, Alexander,Gabor, Barbara,Fürstner, Alois
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supporting information
p. 7731 - 7738
(2013/07/19)
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- Oxidative heck vinylation for the synthesis of complex dienes and polyenes
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We introduce an oxidative Heck reaction for selective complex diene and polyene formation. The reaction proceeds via oxidative Pd(II)/sulfoxide catalysis that retards palladium-hydride isomerizations which previously limited the Heck manifold's capacity f
- Delcamp, Jared H.,Gormisky, Paul E.,White, M. Christina
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supporting information
p. 8460 - 8463
(2013/07/19)
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- Macrolides and alcohols as scent gland constituents of the Madagascan frog mantidactylus femoralis and their intraspecific diversity
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Acoustic and, to a lesser degree, visual signals are the predominant means of signaling in frogs. Nevertheless, certain lineages such as the mantelline frogs from Madagascar use the chemical communication channel as well. Males possess femoral glands on the hind legs, which recently have been shown to contain volatile compounds used in communication as pheromones. Many mantelline species occur in sympatry, and so far species recognition is regarded to occur mainly by acoustic signals. The analysis of the gland constituents of Mantidactylus femoralis by GC/MS revealed the presence of volatile macrolides and secondary alcohols. The new natural products mantidactolides A (4) and B (6), as well as several methyl carbinols, were identified, and their structures were confirmed by synthesis. The analysis of individuals from different locations of Madagascar revealed the presence of two groups characterized by specific patterns of compounds. While one group contained the alcohols and mantidactolide B, the other showed specific presence of the macrolides phoracantholide I (1) and mantidactolide A (4). Genetic analysis of some individuals showed no congruence between genetic relatedness and gland constituents. Several other individuals from related species had different gland compositions. This suggests that a basic set of biosynthetic machinery might be available to a broader group of related species.
- Poth, Dennis,Peram, Pardha Saradhi,Vences, Miguel,Schulz, Stefan
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supporting information
p. 1548 - 1558
(2013/10/22)
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- Rhodium-phosphoramidite catalyzed alkene hydroacylation: Mechanism and octaketide natural product synthesis
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We describe a method that allows salicylaldehyde derivatives to be coupled with a wide range of unactivated alkenes at catalyst loadings as low as 2 mol %. A chiral phosphoramidite ligand and the precise stoichiometry of heterogeneous base are key for high catalytic activity and linear regioselectivity. This protocol was applied in the atom- and step-economical synthesis of eight biologically active octaketide natural products, including anticancer drug candidate cytosporone B. Mechanistic studies provide insight on parameters affecting decarbonylation, a side reaction that limits the turnover number for catalytic hydroacylation. Deuterium labeling studies show that branched hydride insertion is fully reversible, whereas linear hydride insertion is largely irreversible and turnover-limiting. We propose that ligand (R a,R,R)-SIPHOS-PE effectively suppresses decarbonylation, and helps favor a turnover-limiting insertion, by lowering the barrier for reductive elimination in the linear-selective pathway. Together, these factors enable high reactivity and regioselectivity.
- Von Delius, Max,Le, Christine M.,Dong, Vy M.
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supporting information
p. 15022 - 15032
(2012/11/06)
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- Volatile amphibian pheromones: Macrolides from mantellid frogs from madagascar
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Amphibians like water, but do they also notice volatile compounds in the air? Yes, they do. Macrolides, such as phoracantholide-J (see picture; upper right structure) or the newly discovered natural product gephyromantolide-A (left structure), are used for communication by mantelline frogs from Madagascar. Copyright
- Poth, Dennis,Wollenberg, Katharina C.,Vences, Miguel,Schulz, Stefan
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supporting information; experimental part
p. 2187 - 2190
(2012/04/10)
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- A flexible and unified strategy for syntheses of cladospolides A, B, C, and iso-cladospolide B
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A simple, efficient and flexible strategy for the syntheses of cladospolides A-C and iso-cladospolide B is reported here. This strategy involves Julia-Kocienski olefination and Yamaguchi macrolactonization as key steps, starting from either d-ribose or suitable tartaric acid esters. Although our initial efforts towards cladospolide A involving a ring closing metathetic approach were not successful, changing the mode of ring closure and the use of Julia-Kocienski olefination for the construction of the key intermediate solved this issue and paved the way for the completion of total syntheses of this class of natural products.
- Si, Debjani,Sekar, Narayana M.,Kaliappan, Krishna P.
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body text
p. 6988 - 6997
(2011/11/05)
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- Total synthesis of both enantiomers of macrocyclic lactone aspergillide C
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A facile approach to the total synthesis of both enantiomers of the 14-membered macrolactone aspergillide C is described. The strategy employed was also utilized for the synthesis of C4-epimers of both the enantiomers of aspergillide C. The key reactions include Sharpless kinetic resolution, Achmatowicz reaction, Ferrier type alkynylation, hydrosilylation- protodesilylation, Corey-Bakshi-Shibata (CBS) mediated reduction, and Yamaguchi macrolactonization.
- Srihari,Sridhar
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experimental part
p. 6690 - 6697
(2012/01/03)
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- Convergent synthesis of (+)-aspergillide B via a highly diastereoselective oxocarbenium allylation
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The synthesis of (+)-aspergillide B is described by means of a highly diastereoselective oxocarbenium allylation followed by a cross-metathesis and final Yamaguchi macrolactonization.
- Hendrix, Amanda J. Mueller,Jennings, Michael P.
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scheme or table
p. 4260 - 4262
(2010/09/07)
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- FeCl3-catalyzed highly diastereoselective synthesis of substituted piperidines and tetrahydropyrans
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The eco-friendly and highly diastereoselective synthesis of substituted cis-2,6-piperidines and cis-2,6-tetrahydropyrans is described. The key step of this method is the iron-catalyzed thermodynamic equilibration of 2-alkenyl 6-substituted piperidines and 2-alkenyl 6-substituted tetrahydropyrans allowing the isolation of enriched mixtures of the most stable cis-isomers.
- Guerinot, Amandine,Serra-Muns, Anna,Gnamm, Christian,Bensoussan, Charlelie,Reymond, Sebastien,Cossy, Janine
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supporting information; experimental part
p. 1808 - 1811
(2010/10/03)
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- A chemoenzymatic asymmetric synthesis of methyl (6S,13R)-6,13-dihydroxytetradeca-(2E,4E,8E)-trienoate, a component of Mycosphaerella rubella
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The first asymmetric synthesis of (6S,13R)-6,13-dihydroxytetradeca-(2E,4E,8E)-trienoate has been developed. The key steps of the synthesis were the use of an efficient lipase-catalyzed acylation, a chiral template-driven enantiocontrolled allylation for introducing the stereogenic centers, and a cross-metathesis for controlling the C-8 olefin geometry.
- Sharma, Anubha,Gamre, Sunita,Chattopadhyay, Subrata
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experimental part
p. 1164 - 1167
(2009/09/30)
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- Enzyme- and ruthenium-catalyzed dynamic kinetic asymmetric transformation of 1,5-diols. Application to the synthesis of (+)-Solenopsin A
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Dynamic kinetic asymmetric transformation (DYKAT) of 1,5-diols via combined lipase and ruthenium catalysis provides enantiomerically pure diacetates in high diastereoselectivity, which can serve as intermediates in natural product synthesis. This is demon
- Leijondahl, Karin,Boren, Linnea,Braun, Roland,Baeckvall, Jan-E.
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supporting information; experimental part
p. 1988 - 1993
(2009/08/07)
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- Enantiopure 1,5-diols from dynamic kinetic asymmetric transformation. useful synthetic intermediates for the preparation of chiral heterocycles
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Dynamic kinetic asymmetric transformation (DYKAT) of a series of 1,5-diols has been performed in the presence of Candida antarctica lipase B (CALB), Pseudomonas cepacia lipase II (PS-C II), and ruthenium catalyst 4. The resulting optically pure 1,5-diacet
- Leijondahl, Karin,Boren, Linnea,Braun, Roland,Baeckvall, Jan-E.
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supporting information; experimental part
p. 2027 - 2030
(2009/04/10)
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- Combination of RCM and the Pauson-Khand reaction: One-step synthesis of tricyclic structures
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The combination of ring-closing metathesis (RCM) followed by an intramolecular Pauson-Khand reaction gives direct entry to tricyclic compounds. The RCM was carried out on a hexacarbonylcobalt-complexed alkyne, this complex acting as a protecting group against enyne metathesis. The procedure was studied for dienynes containing heteroatoms and allows the building of [6,5,5] and [7,5,5] tricyclic systems. The feasibility of the process depends strongly on the nature of the substrate. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Rosillo, Marta,Arnaiz, Eduardo,Abdi, Delbrin,Blanco-Urgoiti, Jaime,Dominguez, Gema,Perez-Castells, Javier
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experimental part
p. 3917 - 3927
(2009/04/07)
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- Practical synthesis of (E)-α,β-unsaturated carboxylic acids using a one-pot hydroformylation/decarboxylative Knoevenagel reaction sequence
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Combining the regioselective room temperature/ambient pressure hydroformylation and a modification of the Doebner-Knoevenagel reaction allowed for the development of an efficient, one-pot procedure for the synthesis of (E)-α,β-unsaturated carboxylic acids. The reaction proceeds under mild conditions, tolerates a variety of functional groups and gives (E)-α,β-unsaturated carboxylic acids in good yields and with excellent regio-and stereocontrol. The practicability of this process has been demonstrated by a short protecting group-free synthesis of the queen honeybee pheromones 9-ODA[( E)-9-oxodec-2-enoic acid] and 9-HDA[( E)-9-hydroxydec-2-enoic acid].
- Kemme, Susanne T.,?mejkal, Tomá?,Breita, Bernhard
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scheme or table
p. 989 - 994
(2009/05/27)
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- Palladium-catalyzed potassium enoxyborate alkylation of enantiopure Hajos-Parrish indenone to construct rearranged steroid ring systems
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(Chemical Equation Presented) Here we report the stereo- and regiospecific C-6 alkylation of a trans-inden-5-one (from optically pure Hajos-Parrish ketone) with allylic electrophiles. Use of this alkylation procedure has led to an improved synthesis of th
- Jastrzebska, Izabella,Scaglione, Jamie B.,DeKoster, Gregory T.,Rath, Nigam P.,Covey, Douglas F.
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p. 4837 - 4843
(2008/02/05)
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- Stereoselective synthesis of (+)-diplodialides-B, C and a formal synthesis of (+)-diplodialide-A by ring-closing metathesis approach
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Stereoselective synthesis of diplodialides-B and C and the formal synthesis of diplodialide-A are reported. A combination of Jacobsen's hydrolytic kinetic resolution and Sharpless epoxidation is used for the creation of two stereogenic centers, while a ring-closing metathesis strategy was used for the construction of the lactone ring.
- Sharma,Reddy, K. Laxmi
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p. 3197 - 3202
(2007/10/03)
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- Assignment of absolute configuration of natural abundance deuterium signals associated with (R)- and (S)-enantioisotopomers in a fatty acid aligned in a chiral liquid crystal: Enantioselective synthesis and NMR analysis
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Previous experimental natural abundance deuterium (NAD) NMR results have shown an odd/even-related alternation in the (2H/1H) ratio of the methylene groups of fatty acids (ChemBioChem 2001, 2, 425) and, by NAD NMR in CLC, a marked difference between enantiotopic deuterons for each methylenic site (Anal. Chem. 2004, 76, 2827). However, to date, the assignment of the absolute configuration for each deuterium has not been possible. To investigate further the origin of these effects, the assignment of NAD quadrupolar doublets observed in chiral oriented solvent is required. Here we describe the assignment of R- and S-isomers resulting from the isotopic substitution in positions 4 and 5 in the aliphatic chain of 1,1′- bis(thiophenyl)hexane 1 (BTPH) derived from natural linoleic acid of plant origin. This was achieved using an optimized synthetic strategy to obtain separately four regio- and stereoselectively deuterated enantiomers of BTPH. By reference to the deuterium spectra of these isotopically labeled reference compounds, we demonstrate that, on both 4 and 5 positions of BTPH, the isotopic enantiomers of S configuration are depleted relative to those of R configuration. This finding effectively explains the observed low ( 2H/1H) ratio in NAD of some ethylenic sites of unsaturated fatty acids.
- Baillif, Vincent,Robins, Richard J.,Billault, Isabelle,Lesot, Philippe
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p. 11180 - 11187
(2007/10/03)
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- Partially fluorinated liquid crystal material
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The invention provides LC compositions that exhibit V-shaped switching when aligned in an analog device configuration and exhibit bistability when aligned in a bookshelf-type device configuration. The invention more specifically provides LC compositions of formula 1 and particularly chiral nonracemic compounds of formula 1 which exhibit bistable switching as well as V-shaped switching when aligned in appropriate device configurations. The invention also provides methods of using the compounds of the invention in making LC compositions and electooptical devices comprising an aligned layer of the compositions of this invention.
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- Determining the Scope of the Organolanthanide-Catalyzed, Sequential Intramolecular Amination/Cyclization Reaction: Formation of Substituted Quinolizidines, Indolizidines, and Pyrrolizidines
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The scope of the lanthanide-mediated, intramolecular amination/cyclization reaction was determined for the formation of substituted quinolizidines, indolizidines, and pyrrolizidines. A methyl group was installed at diverse positions in the substrates to d
- Molander, Gary A.,Pack, Shawn K.
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p. 9214 - 9220
(2007/10/03)
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- Formation of macrocycles via ring-closing olefin metathesis
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The enhanced metathesis activity of 1,3-dimesityl-4,5-dihydroimidazole-2-ylidene ruthenium carbene catalyst 3 significantly increases the feasibility of synthesizing macrocyclic compounds. Catalyst 3 exhibits sufficient activity in RCM to dimerize α,β-unsaturated ester substrates and afford the corresponding head-to-tail (E,E)-dimeric (and trimeric) macrocycles. The dimerization appears to be under thermodynamic control with the product mixture dependent not only on the electronic and steric nature of the substrate but also on concentration.
- Choon Woo Lee,Grubbs
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p. 7155 - 7158
(2007/10/03)
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- Exploiting the reversibility of olefin metathesis. Syntheses of macrocyclic trisubstituted alkenes and (R,R)-(-)-pyrenophorin.
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[figure: see text] The formation of the trisubstituted cycloalkene 7 by RCM of diene 5 proceeds via the acyclic dimer 6, thus demonstrating the ready reversibility of olefin metathesis if catalyzed by "second generation" ruthenium carbene complexes such as 2-4. When applied to acrylate 11, these catalysts trigger a cyclooligomerization process that evolves with time and serves as key step en route to the lactide antibiotic (-)-pyrenophorin 8.
- Fuerstner,Thiel,Ackermann
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p. 449 - 451
(2007/10/03)
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- Flexible molecules with defined shape. Part 3.1 Conformational analysis of bis(tetrahydropyran-2-yl)methanes
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(R,R)-Bis(tetrahydropyran-2-yl)methane 4 along with its racemate have been synthesized. MM3 calculations suggest that the conformer 4a should be populated to ca. 85% in the conformer equilibrium. Analysis of the 1H NMR coupling constants show that one conformer predominates by about 9:1. That this is the conformer 4a is shown by various NMR techniques, as well as by comparison of calculated with measured CD spectroscopic data. The study is extended to the methyl-substituted bis(tetrahydropyranyl)methanes 21 and 23 which show, as predicted from MM3 calculations, essentially mono-conformational behaviour.
- Hoffmann, Reinhard W.,Colin Kahrs,Schiffer, Jan,Fleischhauer, Joerg
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p. 2407 - 2414
(2007/10/03)
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- Intramolecular Carbometallation of Organozinc Reagents
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The intramolecular cyclization reaction of primary or secondary alkenylzincs leads to a cyclopentylmethylzinc derivatives in a totally regiospecific 5-exo-trig cyclization in the presence of a highly sensitive function.
- Meyer, Christophe,Marek, Ilane,Courtemanche, Gilles,Normant, Jean-F.
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p. 11665 - 11692
(2007/10/02)
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- Enantioselective Preparation of sec. Alcohols from Aldehydes and Dialkyl Zinc Compounds, Generated in situ from Grignard Reagents, Using Substoichiometric Amounts of TADDOL-Titanates
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Using the Schlenk trick (precipitation of MgX2 from etheral solutions by the addition of 1,4-dioxane) mixtures of a Grignard reagent RMgX (X = Cl, Br, I) and 0.5 equiv.ZnCl2 in Et2O can be converted to zinc alkyls R2Zn which in turn are added with enantioselectivities of up to 99:1 to aliphatic and aromatic aldehydes in the presence of Ti(OCHMe2)4 and a chiral titanate derived from an α,α,α',α'-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL).Grignard reagents containing remote double bonds, benzene rings, or acetal groups can also be employed.Different TADDOLs are compared with respect to their usefulness in this kind of enantioselective reactions.
- Bussche-Huennefeld, Joanna Linda v.,Seebach, Dieter
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p. 5719 - 5730
(2007/10/02)
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- Solvolysis Rates and β-Deuterium Secondary Kinetic Isotope Effects of Some Tertiary and Secondary Alk-5-enyl Derivatives. Evidence for ?-Participation
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Tertiary 1,1-dimethylalk-5-enyl chlorides solvolyze in 80percent v/v ethanol with no or moderate rate enhancements attributable to ?-participation.However, secondary β-deuterium kinetic isotope effects (KIE, two deuterated methyl groups) are significantly reduced (kH/kD = 1.22-1.57) relative to the saturated analogues (kH/kD = 1.80), indicating participation of the double bond.Secondary 1-methylalk-5-enyl tosylates show the same trends, i.e., no or very moderate rate enhancements but reduced β-deuterium secondary KIE relative to the saturated analogue.
- Orlovic, Mirko,Borcic, Stanko,Humski, Kresimir,Kronja, Olga,Imper, Vera,et al.
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p. 1874 - 1878
(2007/10/02)
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- Concerning the Mechanism of Grignard Reagent Formation. Evidence for Radical Escape and Return to the Surface of Magnesium
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A study of the mechanism of formation of Grignard reagents using alkyl halide radical probes has been conducted.The effects of activation of the magnesium, temperature, concentration of the alkyl halide, magnesium to alkyl halide ratio, magnesium purity, the nature of the alkyl group, the nature of the halide group, and solvent (viscosity and basicity) on the formation of Grignard reagent were studied.The data obtained were used to test the earlier report by Garst that alkyl radicals, generated in the reaction of an alkyl halide with magnesium, diffuse freely into the solvent phase and return to the magnesium surface to form Grignard reagent.In this study cyclizable radical probes and radical traps were employed to study the extent to which radicals leave and return to the surface of magnesium to form Grignard reagent.In the particular system reported here, the data indicate that ca.25percent of the Grignard reagent is formed from radicals that diffuse into the solvent phase and than return to the magnesium surface to form Grignard reagent.
- Ashby, E. C.,Oswald, John
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p. 6068 - 6076
(2007/10/02)
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- Selective Cyclization and Pinacolization Directed by Tetraalkylammonium Ions
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The effect of the electrolyte composition on the cathodic reduction of cyclohexanone and 6-hepten-2-one was investigated.It was found that addition of catalytic amounts of certain tetraalkylammonium salts to the electrolysis solution alters the reaction pathways.Using a mercury cathode in DMF, dimethylpyrrolidinium (DMP+) tetrafluoroborate, shifts the potential required for preparative reduction to less negative values and changes the reaction products.Cyclohexanone yields the corresponding pinacol and 6-hepten-2-one is stereoselectively cyclized to cis-1,2-dimethylcyclopentanol (95percent).In the absence of DMP+ both substrates are reduced to the corresponding simple alcohols.Stereoselective reductive cylization in DMF can also be induced by tetraethylammonium cations (TEA+) on mercury and by either DMP+ or TEA+ on graphite electrodes.The combination of DMR+ and mercury results in excellent chemical yield and current efficiency.On the basis of results of preparative electrolyses under various conditions and cyclic voltammograms, a mechanism involving the initial reduction of the catalyst cation with participation of the electrode material is proposed.It is suggested that catalysis by specific tetraalkylammonium ions can lead to a preference for one-electron reaction routes.
- Kariv-Miller, Essie,Mahachi, Tendai J.
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p. 1041 - 1045
(2007/10/02)
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- FREE RADICAL REARRANGEMENTS OF ORGANOCOBALOXIMES: ALKYNYL TO CYCLOALKYLIDENE AND HEXENYL TO CYCLOPENTYLMETHYL
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Under irradiation by tungsten light in pyridine solution, several substituted alkylcobaloximes undergo rearrangement to more stable substituted alkyl- or alkenyl-cobaloximes.When the same reactions are carried out in the presence of carbon tetrachloride or chloroform, no rearranged organobaloximes are obtained, but a variety of organic products are obtained derived from the interception of transient organic radicals by the halogenated solvent.The rearrangements are rationalised in terms of a reversible homolysis of the carbon-cobalt bond, rearrangement of the organic radical and recapture by the cobalt(II) fragment to give complexes that are more stable to irradiation than their precursors.
- Bougeard, Peter,Cooksey, Christopher J.,Johnson, Michael D.,Lewin, Melanie J.,Mitchell, Stewart,Owens, Paul A.
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p. 349 - 358
(2007/10/02)
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- Free Radical Chain Nucleophilic Substitution Reactions of 1-Chloro-1-cyclopropyl-1-nitroethane and 2-Chloro-2-nitrohept-6-ene.
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1-Chloro-1-cyclopropyl-1-nitroethane and 2-chloro-2-nitrohept-6-ene underwent free radical chain substitution reactions in which the chlorine was replaced by the nucleophiles Me2C=NO2-, c-C3H5C(CH3)=NO2-, CH2=CH(CH2)3C(CH3)=NO2-, (EtO2C)2CMe-, Me3C(O-=CH2 or the enolate anion of 2-methyl-1,3-cyclopentanedione.Ring opening or closure reactions were not observed in these substitutions or in the reaction of 1-chloro-1-cyclopropyl-1-nitroethane with (n-Bu)3SnH to form 1-cyclopropyl-1-nitroethane.A 1-nitro substituent retards the rate of the cyclopropylcarbinyl radical ring opening by a factor of the at least 104 at 40 deg C.
- Russell, Glen A.,Dedolph, D. F.
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p. 2498 - 2502
(2007/10/02)
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- Further Studies of Substitution Reactions of Stannyl and Germyl Anionoids with Alkyl Bromides. Rearrangement of the 6-Hepten-2-yl Moiety
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The stereochemical outcomes of reactions of (trimethyltin)lithium, (dimethylphenyltin)lithium, (methyldiphenyltin)lithium, and (triphenyltin)lithium in tetrahydrofuran with trans- and cis-2-,3-, and 4-methylcyclohexyl bromides have been determined on the basis of 1H and 13C NMR spectroscopy.The (C6H5)3SnLi reactions proceed stereospecifically with inversion at carbon, while the (CH3)3SnLi reactions are nonstereospecific, as observed previously in some other systems. cis- and trans-2-methoxybromocyclohexanes and -cyclopentanes were also reacted with (CH3)3SnLi, and lowyields of (2-methoxycyclohexyl)- and (2-methoxycyclopentyl)trimethylstannanes were isolated.On the basis of 13C NMR spectra and deoxystannylation reactions , the former is largely ( 90percent) trans while the latter is exlusively trans.The pronounced stereochemical distinction between reactions of (CH3)3SnLi and (C6H5)3SnLi with cyclohexyl bromides is not observed in corresponding reactions of (CH3)3GeLi and (C6H5)3GeLi; both are nonspecific.Certain reactions of cyclopropylcarbinyl bromide and 6-bromo-1-hexene with R3SnLi and R3GeLi (R=CH3 or C6H5) were also studied.Rearranged product (allylcarbinyl) was observed in the reaction of cyclopropylcarbinyl bromide with (CH3)3SnLi, but cyclopentylmethyl products (from cyclization of any hex-5-enyl free radical) was not observed in any case.However, with the secondary 6-bromo-1-heptene all reagents studied (with the exception of (C6H5)3SnLi) afforded rearranged (2-methylcyclopentyl)methyl products, consistent with the intervention of the free radical, wich cyclizes rapidly.Some further estimates of the conformational A values of R3Ge and R3Sn are reported, and triphenyl derivatives have significantly larger values.
- Kitching, William,Olszowy, Henry A.,Harvey, Karen
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p. 1893 - 1904
(2007/10/02)
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