- ν-alkoxy-β-ketoiminate complexes of groups 4 and 5: Synthesis and characterization of the complexes [(η-C5H4R)M{CH3C(O)CHC(NCH 2CHR'O)CH3}Cln] (M = Ti, n = 1; M = Nb, n = 2; R = H, Me; R′ = H, Me), [Ti{CH3C(O)CHC(NCH2CHR'O)CH3}Cl 2(thf)]
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The synthesis and characterization of a range of ν-alkoxo β-ketoiminate complexes of groups 4 and 5 are reported. Reactions between the acylic ν-hydroxyalkyl β-ketoimines CH3C(O)CII2C(NCH2CHR'OH)CH3 (R′ = H, Me) and [(η2-C5H4R)TiCl3] (R = H, Me) in the presence of triethylamine afford the monocyclopentadienyl derivatives [(η-C5H4R)Ti-{CH3C(O)CHC(NCH 2CHR'O)CH3}C1] (R = H, R′ = H, 2a; R = Me, R′ = H, 2b; R = H, R′ = Me, 2c; R = Me, R′ = Me, 2d). Complex 2a adopts a square pyramidal coordination geometry with the Cp occupying the apical site and the terdentate ketoiminate and chloride occupying basal positions. Upon standing in thf, solutions of 2a-d containing NEt3HCl deposit deep orange crystals of [Ti{CH3C(O)CHC(NCH2CHR'O)CH3}Cl2(thf)] (R′ = H, 3a; R′ = Me, 3b) via protonolysis of the Ti-Cp bond. Alternatively, compounds 3a and 3b can be prepared in near quantitative yield either from the reaction between [TiCl4(thf)2] and the corresponding acylic ν-hydroxyalkyl β-ketoimine, in the presence of NEt3, or via a ligand exchange reaction between [Ti(OPri)2Cl2] and the ν-hydroxyalkyl β-ketoimine. Variable-temperature 2H NMR studies of 3a and 3b have shown that stereoisomers of these complexes interchange via a dissociative dynamic process, involving the trigonal bypyramidal intermediate [Ti-{CH3C(O)CHC(NCH2CHR′O)CH3}Cl 2]. The free energy of activation associated with this exchange has been determined (ΔG = 45.5 kJ mol-1, 3a; ΔG = 47.0 kJ mol-1, 3b). Surprisingly, treatment of [TiCOPri4] with ν-hydroxyalkyl β-ketoimine (1:1) results in complete alcoholysis to afford [Ti{CH3C(O)CHC(NCH2CHR'O)CH3}2] (R′ = H, 4a; R′ = Me, 4b), which contain two meridianally coordinated terdentate ketoiminate ligands. The reactions between ν-hydroxyalkyl β-ketoimine derivatives and [(η2-C5H4R)NbCl4] afford [(η2C5H4R)Nb{CH3C(O)CHC(NCH 2CHR'O)CH3}Cl2] (R = H, R′ = H, 5a; R = Me, R′ = H, 5b; R = H, R′ = Me, 5c; R = Me, R′ = Me, 5d). A single-crystal X-ray study of 5a revealed a structure based on an octahedral geometry, such that the nitrogen of the mer-terdentate ligand is trans to the Cp and the two chloro ligands mutually trans. The single-crystal X-ray structures of 2a, 3a, 3b, 4a-CH3Cl3, and 5a are reported.
- Doherty, Simon
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Read Online
- Total synthesis of the Cephalotaxus norditerpenoids (±)-cephanolides A-D
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Concise syntheses of the Cephalotaxus norditerpenoids cephanolides A-D (8-14 steps from commercial material) using a common late-stage synthetic intermediate are described. The success of our approach rested on an early decision to apply chemical network analysis to identify the strategic bonds that needed to be forged, as well as the efficient construction of the carbon framework through iterative Csp2-Csp3 cross-coupling, followed by an intramolecular inverse-demand Diels-Alder cycloaddition. Strategic late-stage oxidations facilitated access to all congeners of the benzenoid cephanolides isolated to date.
- Haider, Maximilian,Sennari, Goh,Eggert, Alina,Sarpong, Richmond
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supporting information
p. 2710 - 2715
(2021/03/01)
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- A short route to access oxaspiro[: N,3,3]propellanes
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Novel access to oxaspiro[n,3,3]propellanes has been developed from bicyclic lactones directly prepared by a photochemical hydroxymethylation or alternatively by a three-step sequence. Thanks to the presence of additional hydroxy- and propargylic groups, a second cyclization catalyzed by silver or bismuth salts, led to the propellane structure which was finally transformed into spiranic derivatives by a Simmons-Smith reaction or condensation with α-ketoesters.
- Nassar, Youssef,Piva, Olivier
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supporting information
p. 5811 - 5815
(2020/08/21)
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- Asymmetric total synthesis of ieodomycin B
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Ieodomycin B, which shows in vitro antimicrobial activity, was isolated from a marine Bacillus species. A novel asymmetric total synthetic approach to ieodomycin B using commercially available geraniol was achieved. The approach involves the generation of 1,3-trans-dihydroxyl at C-3 and C-5 positions via a Crimmins-modified Evans aldol reaction and a chelation-controlled Mukaiyama aldol reaction of a p-methoxybenzyl-protected aldehyde, as well as the generation of a lactone ring in a deprotection-lactonization one-pot reaction.
- Lin, Shuangjie,Zhang, Jianting,Zhang, Zhibin,Xu, Tianxiang,Huang, Shuangping,Wang, Xiaoji
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- New synthetic method of antibacterial natural product Ieodomycin B
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The invention discloses a new synthetic method of antibacterial natural product Ieodomycin B. The method includes the steps of taking a compound of the known formula 7 as a starting material, and synthesizing a target molecule through a series of reactions such as the Evans aldol reaction, the Weinreb amidation reaction, the methoxy benzyl protection reaction, the Mukaiyama aldol reaction, the cyclization reaction. The new synthetic method has the advantages of being unique and novel in design of the whole route, mild in reaction process and condition, high in speed, relatively little in side reaction, and easy and convenient to operate, and using conventional chemical reagents in the route so that the raw materials are cheap and easy to obtain, so as to reduce the synthetic cost greatly.
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Paragraph 0038
(2017/10/26)
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- Synthesis of axially chiral 1,8-diarylnaphthalene ligands and application in asymmetric catalysis: An intriguing fluorine effect
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A fluorinated and a non-fluorinated axially chiral 1,8-diarylnaphthalene ligand have been synthesized through an Ullmann and Suzuki coupling reaction based strategy. A practical methodology for the successful chiral resolution of the newly synthesized catechol based moiety is presented. We also disclose the preliminary application of these axially chiral molecules as ligands in asymmetric transformation reactions.
- Ghosh, Harisadhan,Vavilala, Ravishashidhar,Szpilman, Alex M.
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- Total Synthesis of (+)-7-epi-Tarchonanthuslactone via a Chelation-Controlled Mukaiyama Aldol Reaction
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An asymmetric total synthesis of (+)-7-epi-tarchonanthuslactone was achieved from commercially available methyl (R)-3-hydroxybutyrate. The key step employed a diastereoselective chelation-controlled Mukaiyama aldol reaction to construct the chiral hydroxyl group at the C-5 position.
- Huang, Shuangping,Liu, Dongwang,Tang, Linjun,Huang, Fei Fei,Zhang, Jianting,Wang, Xiaoji
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p. 1240 - 1247
(2015/03/30)
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- A general and enantioselective approach to pentoses: A rapid synthesis of PSI-6130, the nucleoside core of sofosbuvir
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An efficient route towards biologically relevant pentose derivatives is described. The de novo synthetic strategy features an enantioselective α-oxidation reaction enabled by a chiral amine in conjunction with copper(II) catalysis. A subsequent Mukaiyama aldol coupling allows for the incorporation of a wide array of modular two-carbon fragments. Lactone intermediates accessed via this route provide a useful platform for elaboration, as demonstrated by the preparation of a variety of C-nucleosides and fluorinated pentoses. Finally, this work has facilitated expedient syntheses of pharmaceutically active compounds currently in clinical use.
- Peifer, Manuel,Berger, Rapha?lle,Shurtleff, Valerie W.,Conrad, Jay C.,Macmillan, David W. C.
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supporting information
p. 5900 - 5903
(2014/05/20)
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- The 'Mikami'-catalyst in enantioselective diels-alder reactions of juglone-based dienophiles with different 1-oxygenated dienes: An investigation on the substitution pattern dependent regioselectivity
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A mechanistic study investigating the substitution pattern depending regioselectivity of enantioselective BINOL-Ti-catalyzed Diels-Alder reactions of juglone-based dienophiles with 1-oxygenated dienes is reported. The different influences of residues both on the diene as well as on the dienophiles are investigated giving a detailed picture of their role on the regioselectivity.
- B?se, Dietrich,Frey, Wolfgang,Pietruszka, J?rg
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supporting information
p. 2524 - 2532
(2014/11/08)
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- Lithium-titanium exchange of tertiary α-sulfonyl carbanions: Synthesis, structure, dynamics and reactivity of bis(1-sulfonylalkyl) titaniums
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Lithium-titanium exchange of tertiary α-sulfonyl carbanions with ClTi(OiPr)3 and Cl2Ti(OiPr)2 in diethyl ether gave bis(1-sulfonylalkyl) titaniums and not the corresponding (1-sulfon-ylalkyl) titaniums. X-ray crystal structure analysis of di(iso-propoxy) bis[1-(phenylsulfonyl) cyclobutyl]titanium and di-(isopropoxy) bis[1-(phenylsulfonyl) isopropyl]titanium showed asymmetric distorted octahedral complexes, having hexaco-ordinate Ti atoms, two C-Ti bonds, four Ti-O bonds, and two four-membered Ti-O-S-Cα rings. According to 1H NMR spectroscopy bis(1-sulfonylcycloalkyl) titaniums are non-flux-ional at room temperature. This suggests that chiral bis(1-sulfonylalkyl) titaniums should be configurationally stable. The bis(1-sulfonylalkyl) titaniums are stable at room temperature towards β-H elimination. They selectively add to benzaldehyde in the presence of acetophenone but do not react with methyl iodide. The reaction of tertiary acyclic α-sulfonyl carbanions with ClTi(OiPr)3 in tetrahydrofuran (THF) gives different titanium derivatives with unspecified structures, which not only selectively react with benzaldehyde in the presence of acetophenone but are also alkylated by methyl iodide.
- Hess, Thomas,Raabe, Gerhard,Gais, Hans-Joachim
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p. 7134 - 7147
(2015/03/04)
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- The 'Mikami'-Catalyst in Enantioselective Diels-Alder Reactions of Juglone-Based Dienophiles with Different 1-Oxygenated Dienes: An Investigation on the Substitution Pattern Dependent Regioselectivity
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A mechanistic study investigating the substitution pattern depending regioselectivity of enantioselective BINOL-Ti-catalyzed- Diels-Alder reactions of juglone-based dienophiles with 1-oxygenated dienes is reported. The different influences of residues both on the diene as well as on the dienophiles are investigated giving a detailed picture of their role on the regioselectivity.
- B?se, Dietrich,Frey, Wolfgang,Pietruszka, J?rg
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supporting information
p. 2524 - 2532
(2015/12/26)
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- Asymmetric synthesis of andavadoic acid via base-catalyzed 5-exo-tet cyclization of a β-hydroperoxy epoxide
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The first total synthesis of andavadoic acid, a naturally occurring five-membered ring peroxide, and its absolute configuration assignment are reported. Central to this venture was the development of an effective synthesis of a key β-hydroperoxy epoxy ester from (R)-epichlorohydrin via chemoselective methylenation with Nysted reagent in the presence of Ti(Oi-Pr)2Cl2 and chemo- and regioselective Mukaiyama-Isayama peroxidation. This approach also featured the construction of the 1,2-dioxolane ring system by an efficient base-promoted 5-exo epoxide opening by a hydroperoxy group.
- Barnych, Bogdan,Fenet, Bernard,Vatèle, Jean-Michel
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p. 334 - 340
(2013/01/15)
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- Stereoselective amine addition to six-membered cyclic nitronates promoted by silyl triflate
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Six-membered cyclic nitronates couple with amines or their N-silyl derivatives in a diastereoselective fashion to give 3-amino-substituted nitroso acetals in 53-89 % yield through silyl triflate electrophilic catalysis. Stereodifferentiation of this process is determined by thermodynamic control, which is realized due to reversibility of amine addition and a decreased nitrogen inversion barrier in the resulting nitroso acetals. Selected chemical transformations of nitroso acetals were examined. N-Silylamines add to six-membered nitronates with high diastereoselectivity. The reaction follows an original mechanism in which thermodynamic control plays the key role. Copyright
- Mikhaylov, Andrey A.,Dilman, Alexander D.,Khomutova, Yulia A.,Arkhipov, Dmitry E.,Korlyukov, Alexander A.,Ioffe, Sema L.
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supporting information
p. 5670 - 5677
(2013/09/12)
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- Stereoselective synthesis of protected 3-amino-3,6-dideoxyaminosugars
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New syntheses of densely functionalized protected derivatives of 3-amino-3,6-dideoxyaminosugars have been accomplished in an efficient and straightforward manner. The key step of such approaches involves a highly stereoselective titanium-mediated aldol addition of a chiral α-bromo ketone, easily available from lactate esters, to crotonaldehyde. Further functional group transformations, including a new regioselective Staudinger-aza-Wittig reaction of an azidodiacetate, afford in a few steps and high yield the desired carbohydrates as advanced intermediates capable of participating in subsequent glycosylation reactions. The Royal Society of Chemistry 2012.
- Nebot, Joaquim,Romea, Pedro,Urpí, Fèlix
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p. 6395 - 6403
(2012/09/05)
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- Synthesis of pyrrolidine homoazasugars and 3,4-dihydroxy-5- hydroxymethylprolines using aldol additions of metalated bislactim ethers to 2,4-O-ethylidene-d-erythroses
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A strategy for the synthesis of 2,5-dideoxy-2,5-iminohexitols and 2,5-dideoxy-2,5-iminoglyconic acids is described by using diastereoselective aldol additions of metalated bislactim ethers to 2,4-O-ethylidene-d-erythroses and intramolecular N-alkylation a
- Blanco, Olga,Pato, Cristina,Ruiz, Maria,Ojea, Vicente
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p. 2310 - 2321
(2009/09/26)
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- Titanium alkoxides as initiators for the controlled polymerization of lactide
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Fourteen titanium alkoxides were synthesized for comparison of their catalytic properties in the bulk and solution polymerization of lactide (LA). In bulk polymerizations, they are effective catalysts in terms of polymer yield and molecular weight. Titanatranes gave polylactides with significantly increased molecular weight over more extended polymerization times, and those with five-membered rings afforded polymers in higher yields and with larger molecular weights than their six-membered ring counterparts. Steric hindrance of the rings was found to significantly affect polymer yields. Increased heterotactic-biased poly(rac-LA) was formed as the number of chlorine atoms increased in TiClx(O-i-Pr)4-x. In solution polymerizations, titanium alkoxides catalyzed controlled polymerizations of LA, and end group analysis demonstrated that an alkoxide substituent on the titanium atom acted as the initiator. That polymerization is controlled under our conditions was shown by the linearity of molecular weight versus conversion. A tendency toward formation of heterotactic-biased poly(rac-LA) was observed in the solution polymerizations. The rate of ring-opening polymerization (ROP) and the molecular weight of the polymers are greatly influenced by the substituents on the catalyst, as well as by factors such as the polymerization temperature, polymerization time, and concentration of monomer and catalyst.
- Kim, Youngjo,Jnaneshwara,Verkade, John G.
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p. 1437 - 1447
(2008/10/08)
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- Highly efficient ring closure of aromatic dialdehydes to macrocyclic allenes
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The one-pot double deoxygenation of simple alkyl- and polyether-tethered aromatic dialdehydes to give macrocyclic allenes has been accomplished in extraordinarily high yield without the need for slow-addition techniques, using a Ti(IV)-substituted ylide reagent and bis(trimethylsilyl)amide bases. Diastereoselective allene formation occurs when a binaphthyl unit is present in the substrate backbone, and the resulting cyclic allene is characterized by X-ray diffraction. Highly efficient cyclization is proposed to be the result of a combination of preorganization about the amide base counterion and a low concentration of the immediate precursor to Wittig-style olefination ring closure.
- Brody, Marcus S.,Williams, Robin M.,Finn
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p. 3429 - 3433
(2007/10/03)
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- Process for producing optically active dihydropyran derivative
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A process for producing an optically active dihydropyran derivative represented by formula (1): STR1 wherein R1, R2, R3, and R4 each represents a hydrogen atom, a lower alkyl group, a tri-lower alkylsilylmethyl group, a lower alkoxycarbonylamino group, or an --OR5 group, wherein R5 represents a lower alkyl group, a lower acyl group, a lower alkoxycarbonyl group, a di-lower alkylcarbamoyl group, or a tri-lower alkylsilyl group, or R1 and R2 are taken together to form a 5- to 7-membered cyclic hydrocarbon group or to form a condensed heterocyclic group with an oxygen atom, or R2 and R3 are taken together to form a 5- to 7-membered cyclic hydrocarbon group or to form a condensed heterocyclic group with an oxygen atom, provided that all of R1, R2, R3, and R4 do not represent hydrogen atoms at the same time; and R6 represents a lower alkyl group, which comprises reacting a diene compound represented by formula (2): STR2 wherein R1, R2, R3, and R4 have the same meanings as defined above, with a glyoxylic acid ester represented by formula (3): STR3 wherein R6 has the same meaning as defined above, in the presence of a binaphthol-titanium complex represented by formula (4): STR4 wherein X represents a chlorine atom or a bromine atom, is disclosed.
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- Process for producing optically active dihydropyran derivatives
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A process for producing an optically active dihydropyran derivative represented by formula (1): wherein R1 and R4 is each a lower alkyl group or a lower alkoxy group; R2 and R3 is each a hydrogen atom, a lower alkyl group, a lower alkoxy group; and R5 is a lower alkyl group, comprises reacting a diene compound (2): with a glyoxylic acid ester (3): in the presence of an optically active binaphthol-titanium complex (4): wherein X is chlorine or bromine.
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- Asymmetric Diels-Alder Reactions of an Acrylic Acid Derivative Using a Chiral Titanium Catalyst
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Asymmetric Diels-Alder reactions of an acrylic acid derivative using a catalytic amount of a chiral titanium reagent were performed with several dienes.The titanium catalyst was prepared by the alkoxy exchange between dichlorodiisopropoxytitanium(IV) and a chiral 1,4-diol derived from (2R,3R)-tartrate.By the use of the titanium catalyst, the reaction between 3-acryloyl-1,3-oxazolidin-2-one and dienes proceeded in a toluene-petroleum ether mixture in the presence of Molecular Sieves 4A to afford the Diels-Alder adducts in 72-100percent yields and 88 - >96percent enantioselectivity.This reaction can be applied to a diene containing a hetero atom such as 2-ethylthio-1,3-butadiene, which affords the Diels-Alder adduct in a high optical purity.In this paper are also described the methods for determining the optical purities of the obtained 4-substituted 3-cyclohexenecarboxylic acid derivatives.
- Narasaka, Koichi,Tanaka, Hiroko,Kanai, Fumihiko
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p. 387 - 391
(2007/10/02)
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- Enantio- and Diastereo-Selective Synthesis of (+)-Grandisol
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(+)-Grandisol, an insect pheromone having cyclobutane skeleton, is synthesized enantio- and diastereoselectively.The key steps in the synthesis are the asymmetric cycloaddition reaction catalyzed by a chiral titanium reagent and the diastereoselective conjugate addition reaction by the combined use of Me2CuLi and trimethylsilyl trifluoromethanesulfonate.
- Narasaka, Koichi,Kusama, Hiroyuki,Hayashi, Yujiro
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p. 1471 - 1478
(2007/10/02)
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- Catalytic asymmetric glyoxylate-ene reaction: A practical access to α-hydroxy esters in high enantiomeric purities
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An efficient asymmetric catalysis is developed for the glyoxylate-ene reaction to afford the α-hydroxy esters of biological and synthetic importance. The key to the success is the use of the chiral titanium complex prepared in situ from (i-PrO)2TiX2 (X = Cl or Br) and the (R)- or (S)-binaphthol in the presence of molecular sieves (MS 4A). The presence of the molecular sieves (zeolite) is clarified to facilitate the alkoxy-ligand exchange reaction. Thus, the use of MS is shown to be essential for the in situ preparation step of the chiral catalyst and not for the ene reaction step. The present catalytic process is applicable to various 1,1-disubstituted olefins by the judicious choice of the dichloro or dibromo catalyst.
- Mikami, Koichi,Terada, Masahiro,Nakai, Takeshi
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p. 3949 - 3954
(2007/10/02)
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- Process for producing optically active alpha-hydroxycarboxylates
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A process for preparing an α-hydroxycarboxylate represented by formula (I): STR1 wherein R1 represents a hydrogen atom or a lower alkyl group; R2 represents a lower alkyl group, a phenyl group or a cycloalkyl group, or R1 and R2 are bonded to each other to form a five- to seven-membered cycloalkenyl or bicycloalkenyl ring which may be substituted with a lower alkyl group; and R3 represents a lower alkyl group, which comprises reacting an olefin compound represented by formula (II): STR2 wherein R1 ' represents a hydrogen atom or a lower alkyl group; and R2 ' represents a lower alkyl group, a phenyl group or a cycloalkyl group, or R1 ' and R2 ' are bonded to each other to form a five- to seven-membered cycloalkyl or bicycloalkyl ring which may be substituted with a lower alkyl group, with a glyoxylate represented by formula (III): STR3 wherein R3 is as defined above, in the presence of a binaphthol-titanium complex represented by formula (IV): STR4 wherein X represents a chlorine atom or bromine atom.
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- Titanium as a Regio- and Stereo-selective Control Element in the Reaction of α-Alkoxyallylic Phosphine Oxide Anions with Carbonyl Compounds
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A general method is described for directing the condensation of α-methoxyallylphosphine oxide anions (2) with aldehydes, preferentially at the α-position of the allyl system.The procedure, which employs the formation of the titanium ate complex, yields pure diastereoisomers with high stereoselectivity, and these can be used in Horner-Wittig reactions to provide an efficient and convenient synthesis of conjugated methoxydienes of defined geometry.Under the same conditions, acyl halides yield γ-adducts.
- Birse, Ewan F.,McKenzie, Alexander,Murray, Alistair W.
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p. 1039 - 1046
(2007/10/02)
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- Cyclic nitronates from the diastereoselective addition of 1-trimethylsilyloxycyclohexene to nitroolefins. Starting materials for stereoselective Henry reactions and 1,3-dipolar cycloadditions
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Induced by a stoichiometric excess of dichloro(diisopropoxy)-titanium, 1-trimethylsilyloxycyclohexene and (E)-nitroolefins (R-CH=CHNO2, R = C6H5, p-C6H4CH3, p-C6H4OCH3, p-C6H4CN, CH3) combine in CH2Cl2 solution at -90 deg C preferentially with relative topicity ul, opposite to the corresponding reaction of enolates or enamines.The primary products are the epimeric bicyclic nitronates 4-6, which can be separated, and which are converted by KF in MeOH to the alkyl or aryl (nitroethyl)-substituted cyclohexanones 1 and 2 (Table 1).Instead of being solvolysed, the cyclic nitronates 4-6 can be used for nitroaldol additions to give the trisubstituted hexahydrobenzopyranols 15-19.Alternatively, 4-6 can be used in 1,3-dipolar cycloadditions with acrylates to furnish the tricyclic compounds 22-31.In either case, products with four asymmetric carbon atoms (not including acetal centres) are produced diastereoselectively.The addition described here is yet another example of an ul combination of trigonal centres induced by Lewis acids, overriding the influence of the configuration of the donor component.
- Brook, Michael A.,Seebach, Dieter
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p. 836 - 850
(2007/10/02)
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