- Glycal approach to the synthesis of macrolide (-)-A26771B
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A convergent total synthesis of a 16-membered macrolactone natural product (-)-A26771B 1 starting from 3,4,6-tri-O-acetyl-d-glucal 7 is reported. The Ferrier rearrangement of acetylated glucal 7, cross metathesis between chiral fragments 3 and 4, Yamaguchi macrolactonization and selective oxidation of the allylic alcohol are the key features of the synthesis.
- Saidhareddy, Puli,Shaw, Arun K.
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Read Online
- A useful modification of the Kraus procedure1 for preparation of ω-bromo-1-alkenes by HMPA-promoted elimination of HBR from 1,ω-dibromoalkanes
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A reliable, reproducible, general, and detailed procedure for the mono-elimination of hydrogen bromide from 1,ω-dibromoalkanes is described.
- Hoye,Van Veidhuizen,Vos,Zhao
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Read Online
- Mechanistic Insights into FLP-Catalyzed Iodoperfluoroalkylations
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The frustrated Lewis pair-catalyzed iodoperfluoroalkylation of olefins, its substrate activation mode, and catalyst degradation pathways are mechanistically investigated by kinetic measurements. The transformation most likely proceeds via coordination of the phosphane to the perfluoroalkyl iodide and involves radical intermediates.
- Spittler, Michael,Helmecke, Lucas,Czekelius, Constantin
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supporting information
p. 458 - 468
(2018/09/06)
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- Synthesis and characterization of some atypical sphingoid bases
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Sphingolipids are ubiquitous and abundant components of all eukaryotic and some prokaryotic organisms. Sphingolipids show a large structural variety not only between the different species, but also within an individual cell. This variety is not limited to alterations in the polar headgroups of e.g. glycosphingolipids, but also affects the lipophilic anchors comprised of different fatty acids on the one hand and different sphingoid bases on the other hand. The structural variations within different sphingoid bases e.g. in pathogens can be used to identify novel biomarkers and drug targets and the specific change in the profile of common and uncommon sphingolipids are associated with pathological conditions like diabetes or cancer. Therefore, the emerging field of sphingolipidomics is dedicated to collect data on the sphingolipidome of a cell and hence to assign changes therein to certain states of a cell or to pathological conditions. This powerful tool however is still limited by the availability of structural information about the individual lipid species as well as by the availability of appropriate internal standards for quantification. Herein we describe the synthesis of a variety of 1-deoxy-sphingoid bases. 1-DeoxySphingolipids have recently acquired significant attention due to its pathological role in the rare inherited neuropathy, HSAN1 but also as predictive biomarkers in diabetes type II. Some of the compounds synthesized and characterized herein, have been used and will be used to elucidate the correct structure of these disease-related lipids and their metabolites.
- Saied, Essa M.,Le, Thuy Linh-Stella,Hornemann,Arenz, Christoph
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supporting information
p. 4047 - 4057
(2018/06/30)
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- Simple and high yield access to octafunctional azido, amine and urea group bearing cubic spherosilicates
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Spherosilicates and polyhedral oligomeric silsesquioxanes represent unique well-defined rigid building blocks for molecular and hybrid materials. Drawbacks in their synthesis are often low yields and the restricted presence of functional groups either based on incomplete transformation of all corners or the reactivity of the functional groups. Particularly amine-functionalization reveals some synthetic challenges. In this study we report the synthesis of a new class of octafunctionalized hydrogen bond forming spherosilicates via a facile route based on octabromo alkyl functionalized cubic spherosilicates. Four different alkyl chain lengths, namely C4, C5, C6 and C11, were realized starting from ω-alkenylbromides via hydrosilylation of Q8M8H. Using sodium azide in a mixture of acetonitrile:DMF = 10:1, the octaazide was obtained quantitatively and could be rapidly transformed in an octaamine cube via catalytic hydrogenation over Pd/C in absolute ethanol. The following reaction to hydrogen bond forming spherosilicates was performed in situ by adding propyl isocyanate. All transformations proceed quantitatively at the eight corners of the cube, which was evidenced by NMR spectroscopy and ESI-MS measurements. The Q8-target compound can be separated after each reaction step over simple chemical workup while no cage rearrangement was observed. The structures were confirmed using 1H, 13C, 29Si-NMR, FT-IR, elemental analysis and ESI-MS. The method opens a high yield route (overall isolated yield 83-88%) for structural building blocks in hybrid materials.
- Sch?fer, Sandra,Kickelbick, Guido
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supporting information
p. 221 - 226
(2016/12/28)
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- Aromatic Claisen Rearrangements of Benzyl Ketene Acetals: Conversion of Benzylic Alcohols to (ortho-Tolyl)acetates
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Claisen rearrangements of benzyl vinyl ethers are much less facile than those of aliphatic allyl vinyl ethers, and their synthetic utility has remained relatively unexplored. A one-pot procedure is reported for the generation and Claisen rearrangement of benzyl vinyl ethers that contain an activating α-alkoxy substituent on the vinyl group. A [3,3]-sigmatropic mechanism was supported by trapping of the intermediate isotoluene in an intramolecular Alder–ene reaction.
- Burns, Jed M.,Krenske, Elizabeth H.,McGeary, Ross P.
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supporting information
p. 252 - 256
(2017/01/24)
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- PERYLENE TETRACARBOXYLIC ACID BISIMIDE DERIVATIVE, n-TYPE SEMICONDUCTOR, PROCESS FOR PRODUCING n-TYPE SEMICONDUCTOR, AND ELECTRONIC DEVICE
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The present invention provides a perylene tetracarboxylic acid bisimide derivative which enables the formation of an n-type semiconductor having high carrier mobility and has superior solubility. The perylene tetracarboxylic acid bisimide derivative is a perylene tetracarboxylic acid bisimide derivative represented by the following chemical formula (I), a tautomer or stereoisomer of the perylene tetracarboxylic acid bisimide derivative, or a salt of the perylene tetracarboxylic acid bisimide derivative or the tautomer or stereoisomer, In the chemical formula (I), R1 to R6 each represents a hydrogen atom, organooligosiloxane, or any substituent, at least one of R1 to R6 represents a monovalent substituent derived from organooligosiloxane, L1 and L2 each represents a single bond or a linking group, R7 to R10 each represents a lower alkyl group or a halogen, and o, p, q, and r each represents an integer from 0 to 2.
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Paragraph 0103-0105
(2014/03/21)
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- Low catalyst loading in ring-closing metathesis reactions
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An efficient procedure is described for ring-closing metathesis reactions. A conversion of 95 % for diethyl diallylmalonate in dilute solution could be achieved within a few minutes, reaching TOF=4173min-1, with very low loading of commercially available Ru catalysts that contained unsaturated NHC ligands. In general, only 50 to 250ppm of the catalyst is required to achieve near-quantitative conversion into a broad variety of 5-16-membered heterocyclic compounds. The practicality of this procedure was illustrated in the synthesis of 5-8-membered N-tert-butoxycarbonyl (N-Boc)- and N-para-toluenesulfonyl (N-Ts)-protected cyclic amines and 9-16-membered lactones. The synthesis of macrocyclic proline-based lactams required slightly higher catalyst loadings. Along with monocyclic products, oligomeric byproducts, mostly cyclodimers, were isolated and characterized. Getting some closure: An efficient procedure is described for ring-closing metathesis reactions in which only 50 to 250ppm of catalyst is required to effect almost-quantitative conversion into a broad range of 5-16-membered heterocyclic compounds. The practicality of this procedure was illustrated in the synthesis of 5-8-membered N-protected cyclic amines, 9-16-membered lactones, and 11-16-membered proline-based lactams. Copyright
- Kadyrov, Renat
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supporting information
p. 1002 - 1012
(2013/02/23)
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- Synthesis and characterization of ferroelectric liquid crystalline siloxanes containing 4-hydroxyphenyl(2S,3S)-2-chloro-3-methylvalerate
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New series of organosiloxane ferroelectric liquid crystalline materials have been synthesized, and their mesomorphic and physical properties have been characterized. These new series contain bis-siloxane or tris-siloxane unit attached to the flexible alkyl chain end of (2S,3S)-2-chloro-3-methylvalerate. The siloxane molecule induction is helpful to the chiral smectic C (S C) formation and chiral SC* stabilization, and it simultaneously causes the liquid crystal temperature range of chiral S C* to be broader. The siloxane member is helpful in reducing the smectic C (SC) transation shift temperature, and the molecule containing tris-siloxane units shows better effect than the bis-siloxane one. The synthesis and characterization of the new FLCs materials which exhibit SC* phase at room temperature and higher spontaneous polarization are presented.
- Lin, Chih-Hung
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experimental part
p. 33 - 42
(2012/05/04)
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- Syntheses and palladium, platinum, and borane adducts of symmetrical trialkylphosphines with three terminal vinyl groups, P((CH2) mCH=CH2)3
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Reactions of Br(CH2)mCH=CH2 with Mg powder and then PCl3 (0.33 equiv.) afford P((CH2)m-CH=CH 2)3 (1; m = a, 4; b, 5; c, 6; d, 7; e, 8; f, 9; 52-87 %). Reactions of 1a-c, e with PdX2(COD) (X = Cl, Br) give trans-PdX 2(P((CH2)mCH=CH2)3) 2 (35-92 %). Reactions of 1b-e with PtCl2 in benzene give mainly trans-PtCl2(P((CH2)mCH=CH 2)3)2 (trans-5b-e; 52-75 %), whereas those with K2PtCl4 in water give mainly cis-5b-e (33-70 %). The reaction of equimolar quantities of 1c and H3B.S(CH3) 2 gives the 1 : 1 adduct H3B·P((CH 2)6CH=CH2)3 (85 %). In none of these transformations are by-products derived from the C=C linkages observed.
- Nawara-Hultzsch, Agnieszka J.,Skopek, Katrin,Shima, Takanori,Barbasiewicz, Micha,Hess, Gisela D.,Skaper, Dirk,Gladysz, John A.
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body text
p. 414 - 424
(2010/10/01)
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- Carbocationic n-endo-trig cyclizations
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Unsaturated benzyl cations (4-MeOC6H4)CH +-(CH2)n-CH=CH2 (1) have been generated laser-flash photolytically in acetonitrile in the presence of enol ethers or 2-methylfuran. The reactions of the cations 1 (n = 2 and 4) with these π-nucleophiles follow second-order rate laws with rate constants comparable to those of the analogous saturated species (4MeOC6H 4)CH+-(CH2)3CH3. Product studies show the absence of cyclization products. In contrast, the carbocation (4-MeOC6H4)CH+-(CH2) 3-CH=CH2 (Id) undergoes a highly reversible 6endo-trig cyclization which is approximately 107 times faster than the corresponding intermolecular reaction of (4MeOC6H4)CH +-(CH2)3CH3 with hex1-ene. This cyclization yields a highly electrophilic, partially bridged carbocation, which accounts for the finding that Id is consumed eight times faster in trifluoroethanol solution than all other carbocations of this series. Quantum-chemical calculations (B3LYP/6311G(d,p) and MP2/6-31+G(2d,p)) have been performed to elucidate the structures of the involved carbocations. Consequences of these findings on the role of π-participation in solvolysis reactions are discussed.
- Shi, Lei,Horn, Markus,Kobayashi, Shinjiro,Mayr, Herbert
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supporting information; experimental part
p. 8533 - 8541
(2010/03/26)
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- Primary alkyl bromides from dimethylthiocarbamates
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The conversion of primary alkyl dimethylthiocarbamates into alkyl bromides using the Vilsmeier reagent occurs in high yields in the presence of other non-acid sensitive and non-nucleophilic functional groups. Georg Thieme Verlag Stuttgart · New York.
- Moynihan, Meghan F.,Tucker, Joseph W.,Abelt, Christopher J.
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experimental part
p. 3565 - 3568
(2009/06/18)
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- Alkenylsilane structure effects on mononuclear and binuclear organotitanium-mediated ethylene polymerization: Scope and mechanism of simultaneous polyolefin branch and functional group introduction
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Alkenylsilanes of varying chain lengths are investigated as simultaneous chain-transfer agents and comonomers in organotitanium-mediated olefin polymerization processes. Ethylene polymerizations were carried out with activated CGCTiMe2 and EBICGCTi2Me4 (CGC = Me2Si(Me4C5)(NtBu); EBICGC = (μ-CH2CH2-3,3′){(η5-indenyl)[1- Me2Si(tBuN)]}2) precatalysts in the presence of allylsilane, 3-butenylsilane, 5-hexenylsilane, and 7-octenylsilane. In the presence of these alkenylsilanes, high polymerization activities (up to 10 7 g of polymer/(mol of Ti-atm ethylene·h)), narrow product copolymer polydispersities, and substantial amounts of long-chain branching are observed. Regardless of Ti nuclearity, alkenylsilane incorporation levels follow the trend C8H15SiH3 6H 11SiH3 ≈ C4H7SiH3 3H5SiH3. Alkenylsilane comonomer incorporation levels are consistently higher for CGCTiMe2-mediated copolymerizations (up to 54%) in comparison with EBICGCTi2Me 4-mediated copolymerizations (up to 32%). The long-chain branching levels as compared to the total branch content follow the trend C 3H5SiH3 4H7SiH 3 ≈ C6H11SiH3 ≈ C 8H15SiH3, with gel permeation chromatography-multi-angle laser light scattering-derived branching ratios (gM) approaching 1.0 for C8H15SiH3. Time-dependent experiments indicate a linear increase of copolymer Mw with increasing polymerization reaction time. This process for producing long-chain branched polyolefins by coupling of an α-olefin with a chain-transfer agent in one comonomer is unprecedented. Under the conditions investigated, alkenylsilanes ranging from C3 to C8 are all efficient chain-transfer agents. Ti nuclearity significantly influences silanolytic chain-transfer processes, with the binuclear system exhibiting a sublinear relationship between Mn and [alkenylsilane]-1 for allylsilane and 3-butenylsilane, and a superlinear relationship between Mn and [alkenylsilane]-1 for 5-hexenylsilane and 7-octenylsilane. For the mononuclear Ti system, alkenylsilanes up to C 6 exhibit a linear relationship between Mn and [alkenylsilane]-1, consistent with a simple silanolytic chain termination mechanism.
- Amin, Smruti B.,Marks, Tobin J.
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p. 2938 - 2953
(2007/10/03)
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- Synthesis and lead(II) sorption of silica gel-immobilized, di-ionizable calix[4]arenes
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Di-ionizable calix[4]arenes with two lower-rim N-(X)sulfonyl carboxamide groups were covalently linked to silica gel via a single attachment on the upper rim. Both the acidity of the ionizable groups (X group variation) and the length of the spacer that joins the ligands to the silica gel matrix were varied. Preliminary evaluation of these new ion-exchange resins for sorption of lead(II) from aqueous solutions was conducted.
- Zhang, Dongmei,Wang, Jing,Lawson, Thomas R.,Bartsch, Richard A.
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p. 5076 - 5082
(2008/02/01)
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- Alkenylsilane effects on organotitanium-catalyzed ethylene polymerization. Toward simultaneous polyolefin branch and functional group introduction
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The comonomer 5-hexenylsilane is introduced into organotitanium-mediated ethylene polymerizations to produce silane-terminated ethylene/5-hexenylsilane copolymers. The resulting polymers were characterized by 1H and 13C NMR, GPC, and DSC. High activities (up to 107 g polymer/(mol Ti·atm ethylene·h)) and narrow polydispersities are observed in the polymerization/chain transfer process. Ethylene/5-hexenylsilane copolymer molecular weights are found to be inversely proportional to 5-hexenylsilane concentration, supporting a silanolytic chain transfer mechanism. Control experiments indicate that chain transfer mechanism by 5-hexenylsilane is significantly more efficient than that of n-hexylsilane for organotitanium-mediated ethylene polymerization. The present study represents the first case in which a functionalized comonomer is efficiently used to effect both propagation and chain transfer chemistry during olefin polymerization. Copyright
- Amin, Smruti B.,Marks, Tobin J.
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p. 4506 - 4507
(2007/10/03)
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- Batch microwave reactor
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An apparatus for performing batchwise chemical reactions using microwave energy (10-11-12) includes a vessel (15) within a microwave cavity (13). The vessel has a sealed cover (16), located outside cavity (13), which mounts a cold-finger type heat exchanger (24) for immersion in the vessel's contents (23). Cover (16) also mounts a pressure measuring device (17) and a temperature sensing device (20) for monitoring the vessel's contents during a chemical reaction. A pressure operable safety valve (18) and a sampling facility (19) are also mounted on the cover (16). The vessel also contains a magnetically operated stirrer (22). The reactor apparatus is constructed to withstand high pressures and temperatures that may be developed within the vessel (15). Various uses of the cold-finger (24) to facilitate the conduct or completion of a chemical reaction are described.
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- Intramolecular Diels-Alder reactions of 4H-furo[3,4-b]indoles. New syntheses of benzo[a]carbazoles and benzo[c]carbazoles
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Furoindoles 7 and 16 undergo smooth intramolecular Diels-Alder reactions to afford, after dehydration, hydrolysis, and oxidation, benzocarbazoles 11 and 21, respectively.
- Gribble, Gordon W.,Silva, Richard A.,Saulnier, Mark G.
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p. 729 - 747
(2007/10/03)
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- Synthesis of Saturated Anacardic Acids, and Alkenyl and Alkynyl Analogues
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The C-alkylation of esters of 2-methoxy-6-methylbenzoic acid and of the 4-methyl isomers affords a route to homologous compounds including in the former case members of the natural anacardic acids from Anacardium occidentale and ω-alkynyl compounds suitable for synthesising other natural phenolic lipids or for structure/activity studies.
- Tyman, John H. P.,Visani, Naina
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p. 228 - 240
(2007/10/03)
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- Liquid crystalline polymer having a polysiloxane backbone
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A side-chain liquid crystalline polysiloxane having the following formula is disclosed: STR1 wherein Me is methyl; m is an integer of 40 to 80; n is an integer of 1 to 12; Ar is phenylene, biphenylene or naphthalene; Ar' is phenylene or naphthalene; X is halogen or methyl; and R is C1 -C4 alkyl.
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- A New Microwave Reactor for Batchwise Organic Synthesis
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A laboratory-scale microwave batch reactor (MBR) has been developed for organic synthesis or kinetic studies on the 20-100 mL scale, with upper operating limits of 260 deg C and 10 MPa (100 atm).The MBR complements a continuous microwave reactor which was the subject of a previous report from the author's laboratory.Microwave-assisted organic reactions were conducted safely and conveniently in the MBR, for lengthy periods when required, and in volatile organic solvents.The use of water as a solvent for organic reactions was also explored.Examples include oxidation, elimination, esterifications, hydrolysis of a tertiary amide, etherification, isomerization, Hofmann elimination, α-iodination of a carboxylic acid, Claisen rearrangement, aminoreductone formation, and Willgerodt reactions.Advantages of the new MBR include the capability for rapid heating and quenching of reaction mixtures, minimal temperature gradients within the sample, and elimination of wall effects.Safety aspects have been discussed.
- Raner, Kevin D.,Strauss, Christopher R.,Trainor, Robert W.,Thorn, John S.
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p. 2456 - 2460
(2007/10/02)
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- Dilithium tetrachlorocuprate catalyzed coupling of allylmagnesium bromide with α,ω-dihaloalkanes
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Allylmagnesium bromide has been shown to cross-couple with α,ω- dihaloalkanes in the presence of dilithium tetrachlorocuprate to yield, depending on reaction conditions, mono-coupled haloalkenes or di-coupled alkadienes. The order of the reactivity of the dihalides is I > Br >> CI and secondary halides show greater reactivity than primary halides.
- Johnson,Donohoe,Kang
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p. 1557 - 1564
(2007/10/02)
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- Influence of strain on chemical reactivity. Relative reactivity of torsionally distorted double bonds in MCPBA epoxidations
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The second-order reaction rates were measured for the MCPBA epoxidation in CH2Cl2 for a series of cyclic olefins including bridgehead olefms and trans-cycloalkenes. As expected, strained bridgehead alkenes and trans-cycloalkenes showed faster reaction rates than nonstrained cis-cycloalkenes. The MM-2 steric energies of alkenes, alkanes, and their corresponding epoxides were calculated to evaluate the strain energy released in each reaction (ΔSE). Plots of log krel vs olefin strain did not show a good correlation. However, the plot of log krel vs ΔSE (which is defined as the steric energy difference between olefin and the corresponding epoxide) showed a good correlation for each set of di- and trisubstituted olefins. This result suggests that ΔSE directly reflects strain energy relief in the transition state. From the slope for the plot log krel vs ΔSE, it was thought that approximately 42% of strain (ΔSE) was released in the transition state for the MCPBA epoxidation. Also, trialkyl-subtituted alkenes were found to be about 50 times more reactive than dialkyl-substituted alkenes in cases where the strain energy relief (ΔSE) is the same. The reaction rate is also plotted versus ionization potential of the olefin, assuming that the major orbital interaction lies between the LUMO of the peracid and the HOMO of the olefin. Although, in some cases, a rough correlation of the reaction rate with the ionization potential of the olefin exists, the frontier orbital interaction is not viewed as the dominant factor since conjugated alkenes, which have higher HOMO energies than simple olefins, are not more reactive in MCPBA epoxidation.
- Shea, Kenneth J.,Kim, Jang-Seob
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p. 3044 - 3051
(2007/10/02)
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- Photoreactions of Enones with Amines - Cyclization of Unsaturated Enones and Reductive Ring Opening by Photoinduced Electron Transfer (PET)
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Photolysis of the unsaturated enones 1 yields cycloaddition products 2 and 3 with varying regioselectivity.Under electron transfer conditions (PET) spirocyclic products 4 are formed.The straight cycloaddition products 2b, c, f are converted to the spirocyclic products 4b, c, f under the same reaction conditions.The cyclobutane 5 and cyclopropane 11 also undergo this new reductive ring opening reaction, while the stabilized system 7 is converted to reduced ring-enlarged triquinane 10 which may be interesting in natural product synthesis. - Irradiation of 2-cyclohexen-1-one (14) in the presence of N,N-dimethylallylamine (15) leads to the decahydroisoquinoline 18.A mechanism involving radical intermediates is discussed. Key Words: Photoinduced electron transfer / Cyclization / Ring opening / Enones
- Mattay, Jochen,Banning, Anja,Bischof, Eric W.,Heidbreder, Andreas,Runsink, Jan
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p. 2119 - 2128
(2007/10/02)
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- An efficient synthesis of (+)-Anatoxin-a.
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An efficient synthesis (38 percent overall yield in 8 steps starting from 2) of the potent neurotoxin (+)-anatoxin-a is described.The key step involves the stereoselective addition of 5-hexenylcopper to the chiral N-acyliminium ion 2a.
- Skrinjar, Marco,Nilsson, Carita,Wistrand, Lars-G.
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p. 1263 - 1270
(2007/10/02)
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- Synthesis of a germination self-inhibitor, (-)-gloeosporone, and related compounds and evaluation of their activities
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Synthesis of (-)-gloeosporone (1a), isolated from spores of Colletotrichum gloeosporioides as a self-inhibitor for germination, and its three diastereomers was accomplished starting from (S)- and (R)-1-tridecen-8-ol obtained from their (S)-naphthyl ethylcarbamates (8a and 8b), both of which were isolated from the mixture of diastereoisomers derived from racemic 1-tridecen-8-ol (7) and the Pirkle reagent. Biological testing of the compounds showed weak self-inhibitor activity toward germination of the spores.
- Matsushita,Yoshida,Zhang,Miyashita,Irie,Ueno,Tsurushima
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p. 524 - 527
(2007/10/02)
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- Synthesis of Various New Nitroxide Free Radical Fatty Acids
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A generally applicable method is presented for the synthesis of various new nitroxide fatty acid isomers in which the fatty acid chains are attached at different positions of the pyrrolidin-1-oxyl ring.These isomers can be obtained by Michael addition of a nitroalkane to an α,β-unsaturated ketone to give a γ-nitro ketone, followed by ring closure with zinc and ammonium chloride to give a 1-pyrroline N-oxide which then reacts with Grignard reagents to give a pyrrolidin-1-oxyl free radical compound, which undergoes phase transfer oxidation of its terminal unsaturated bond.
- Hideg, Kalman,Lex, Laszlo
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p. 1431 - 1438
(2007/10/02)
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- INTRAMOLECULAR CYCLOADDITIONS WITH ISOBENZOFURANS I
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Intramolecular Diels-Alder reactions with isobenzofurans (5,12) offer an attractive route for the preparation of polycyclic systems (6,13).
- Friedrichsen, Willy,Koenig, B. Michael,Hildebandt, Knut,Debaerdemaeker, Tony
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p. 297 - 302
(2007/10/02)
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- Radical Chain Mechanism for Alkyl Rearrangement in Organocobalt Complexes
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The molecular rearrangement of a series of 5-hexenylcobalt(III) complexes of various Schiff bases is demonstrated to proceed via an unusual radical chain process.Thus the facility with the 5-hexenyl --> cyclopentylmethyl rearrangement occurs is highly dependent on the presence of trace impurities which can vary from the age of a highly purified sample to the presence of air.We find that the rearrangement of (5-hexenyl)CoIII(salen) I can be deliberately controlled by inhibiting it completely or by promoting it rapidly.For example, the addition of cobalt(II), nitroxide (TEMPO), dioxygen, or dihydroanthracene as well as an electrochemical preduction procedure can effectively squelch the 5-hexenyl rearrangement.Conversely, chemical and electrochemical oxidations with a ferrocenium salt and a platinium anode at 0.4 V, respectively, trigger the rearrangement.In each case, the limited molar amounts of additives (or faradays of charge) are sufficiently small to ensure high kinetic chain lenghts.Inhibition and initiation of the chain process by these techniques relate directly to the destruction and generation, respectively, of alkyl radicals as the prime reactive intermediates.Accordingly, a homolytic displacement (SH2) of the alkylcobalt(III) complex is proposed, in conjuction with the well-known rearrangement of the hexenyl radical, to constitute the two-step propagation cycle in Scheme III.Such a mechanism accounts for the intermolecular character of the hexenyl rearrangement as established by crossover experiments and the observation of a concurrent alkyl exchange which would otherwise be difficult to explain.The spontaneous rearrangement of a freshly prepared sample of (hexenyl)CoIII(salen) and the dichotomous effect of pyridine as a donor ligand are both readily accommodated within the content of the mechanism in Scheme III.
- Samsel, E. G.,Kochi, J. K.
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p. 4790 - 4804
(2007/10/02)
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- Synthesis of Heptadeca-1,8Z-diene
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Wittig reaction of methylenetriphenylphosphorane on 5-tetrahydropyranyloxypentanal (II) yields 6-tetrahydropyranyloxyhex-1-ene (III) which produces the alcohol IV on treatment with PTS/methanol.The latter (IV) undergoes smooth conversion into the corresponding bromide (V) on reaction with PBr3/pyridine.Alkylation of propargyl alcohol with n-octyl bromide in the presence of Li/liq.NH3 affords undec-2-yn-1-ol (VI) which on reduction in the presence of Lindlar's catalyst gives undec-2Z-en-1-ol (VII).Reaction of MsCl/TEA on VII in anhyd.CH2Cl2 forms the mesylate (VIII) which on coupling with V provides the title compound (I).
- Vig, O. P.,Sharma, M. L.,Kumari, Sarla,Rani, Veena
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p. 771 - 772
(2007/10/02)
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- INTRAMOLECULAR ALKYLATION OF CYCLOPENTENONES: A GENERAL ROUTE TO CONJOINT RING SYSTEMS
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The intramolecular alkylation of several bromo- and epoxy-2-methylcyclopentenones, 18-23 and 33, are described.In all cases, except 33, alkylative cyclization occours at the γ' position to the conjoint ring systems 25-31.The "blocked" bromide 33 (γ' geminal dimethyl substituent) cyclizes to the fused ring hydrindenones 35 and/or 34 depending upon conditions.Enolate anion generation from 3-ethyl-2-methyl-2-cyclopentenone (36) with various bases (KH, LDA, Et3N) is described and the anion populations determined by quenching with chlorotrimethylsilane to afford the enol ethers 39-41.The intramolecular alkylations are discussed.
- Antczak, Kazimierz,Kingston, John F.,Alward, Sandra J.,Fallis, Alex G.
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p. 829 - 837
(2007/10/02)
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- Palladium-Catalyzed Cyclizations of Bromo Dienes
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1-Bromo 1,5-dienes, 2-bromo 1,6-dienes, and 2-bromo 1,7-dienes have been found to undergo palladiumtriarylphosphine catalyzed cyclizations in the presence of piperidine to form five- or six-membered ring products in good yields.The major or only cyclic products formed are piperidino- or (piperidinomethyl)cyclopentenes and -cyclohexenes.The five-membered ring products are preferred over the six when there is a choice.
- Narula, C. K.,Mak, K. T.,Heck, R. F.
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p. 2792 - 2796
(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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