- Stereoselective total synthesis of (-)-isocladospolide B and cladospolide B and C
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The enantioselective synthesis of bioactive butenolides isocladospolide B, cladospolide B, and cladospolide-C has been achieved from (S)-propylene oxide. Of the three stereogenic centers, the C-4/C-5 vic-diol was obtained using diastereo- and enantio-selective Brown hydroxycrotylation, while the C-11 stereocenter was created by Jacobsen hydrolytic kinetic resolution. Georg Thieme Verlag Stuttgart · New York.
- Yadav,Mandal
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Read Online
- Enantioselective Resolution Copolymerization of Racemic Epoxides and Anhydrides: Efficient Approach for Stereoregular Polyesters and Chiral Epoxides
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Herein we report an efficient strategy for preparing isotactic polyesters and chiral epoxides via enantioselective resolution copolymerization of racemic terminal epoxides with anhydrides, mediated by enantiopure bimetallic complexes in conjunction with a nucleophilic cocatalyst. The chirality of both the axial linker and the diamine backbones of the ligand are responsible for the chiral induction of this kinetic resolution copolymerization process. The catalyst systems exhibit exceptional levels of enantioselectivity with a kinetic resolution coefficient exceeding 300 for various racemic epoxides, affording highly isotactic copolymers (selectivity factors of more than 300) with a completely alternating structure and low polydispersity index. Most of the produced isotactic polyesters are typical semicrystalline materials with melting temperatures in the range from 77 to 160 °C.
- Li, Jie,Ren, Bai-Hao,Wan, Zhao-Qian,Chen, Shi-Yu,Liu, Ye,Ren, Wei-Min,Lu, Xiao-Bing
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supporting information
p. 8937 - 8942
(2019/06/11)
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- An alternative stereoselective total synthesis of (-)-pyrenophorol
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The total synthesis of 16-membered C2–Symmetric dilactone (-)-Pyrenophorol was accomplished starting from commercially available (S)-epoxide prepared by hydrolytic kinetic resolution of (±)–epoxide with key steps of Grignard reaction, Swern oxidation, Wittig reaction and cyclization was achieved by intermolecular Mitsunobu cyclization. The synthesis of (-)-Pyrenophorol accomplished from cheaply available starting material, easily work-up procedures and reduction of cost in industrial process were major advantages of this route.
- Alluraiah, Gurrala,Sreenivasulu, Reddymasu,Chandrasekhar, Choragudi,Raju, Rudraraju Ramesh
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p. 2738 - 2743
(2018/09/25)
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- Homochiral Metal-Organic Cage for Gas Chromatographic Separations
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Metal-organic cages (MOCs) as a new type of porous material with well-defined cavities were extensively pursued because of their relative ease of synthesis and their potential applications in host-guest chemistry, molecular recognition, separation, catalysis, gas storage, and drug delivery. Here, we first reported that a homochiral MOC [Zn3L2] is explored to fabricate [Zn3L2] coated capillary column for high-resolution gas chromatographic separation of a wide range of analytes, including n-alkanes, polycyclic aromatic hydrocarbons, and positional isomers, especially for racemates. Various kinds of racemates such as alcohols, diols, epoxides, ethers, halohydrocarbons, and esters were separated with good enantioselectivity and reproducibility on the [Zn3L2] coated capillary column. The fabricated [Zn3L2] coated capillary column exhibited significant chiral recognition complementary to that of a commercial β-DEX 120 column and our recently reported homochiral porous organic cage CC3-R coated column. The results show that the homochiral MOCs will be very attractive as a new type of chiral selector in separation science.
- Xie, Sheng-Ming,Fu, Nan,Li, Li,Yuan, Bao-Yan,Zhang, Jun-Hui,Li, Yan-Xia,Yuan, Li-Ming
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p. 9182 - 9188
(2018/07/21)
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- Bimetallic Chromium Catalysts with Chain Transfer Agents: A Route to Isotactic Poly(propylene oxide)s with Narrow Dispersities
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Bimetallic chromium catalysts are investigated for the enantioselective polymerization of propylene oxide. The catalyst is composed of two salen chromium species linked by an alkyl chain, the length of which significantly impacts the rate of polymerization. While the use of a chloride initiator on the catalyst resulted in bimodal molecular weight distributions, switching to a trifluoroacetate initiating group and adding a diol chain transfer agent afforded polymers of controllable molecular weight with low, unimodal dispersities.
- Morris, Lilliana S.,Childers, M. Ian,Coates, Geoffrey W.
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supporting information
p. 5731 - 5734
(2018/05/14)
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- Chiral oligomers of spiro-salencobalt(III)X for catalytic asymmetric cycloaddition of epoxides with CO2
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Several new chiral oligomers of spiro-salenCo(III)X (spiro = 1.1′-spirobiindane-7.7′-diol) complexes have been designed, synthesized, and characterized by nuclear magnetic resonance (NMR), infrared (IR), and elemental analyses, in which, the chiral spiro moieties are first introduced into a scaffold of chiral salenCo catalysts. They were used to catalyze the asymmetric cycloaddition of epoxides with carbon dioxide. Under very mild reaction conditions, a kinetic resolution of racemic epoxides with CO2 was smoothly initiated by these chiral oligomer catalysts with good enantioselectivities, which can be attributed to the match effect between chiral backbones of salen and spiro. High stability and easy recyclability are their major advantages.
- Zhu, Zhouhe,Zhang, Yuqian,Wang, Kai,Fu, Xiying,Chen, Fengjuan,Jing, Huanwang
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- POLYESTER STEREOCOMPLEXES, COMPOSITIONS COMPRISING SAME, AND METHODS OF MAKING AND USING SAME
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Compositions comprising stereocomplexes of enantiomeric polymer chains having individual repeat units formed from the reaction of an epoxide and cyclic anhydride. The compositions can be made by mixing two types of enantiomeric polymer chains having opposite absolute stereochemistry. The compositions can be used in applications such as biomedical applications and drug delivery applications.
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Paragraph 0109; 0110
(2016/02/29)
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- Synthesis of (3R,5S)-5-hydroxy-de-O-methyllasiodiplodin: A facile and stereoselective approach
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A concise and facile synthesis of (3R,5S)-5-hydroxy-de-O-methyllasiodiplodin has been demonstrated in 12 steps starting from methylacetoacetate and (±)propylene oxide. The key reactions involved are Jacobsen's hydrolytic kinetic resolution, Sharpless asymmetric epoxidation, Mitsunobu, and ring closing metathesis reaction for the construction of macrolactone with two chiral substitutions on it.
- Bujaranipalli, Sheshurao,Das, Saibal
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p. 3747 - 3749
(2015/06/08)
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- Dinuclear salen cobalt complex incorporating Y(OTf)3: enhanced enantioselectivity in the hydrolytic kinetic resolution of epoxides
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The activation of inactive Jacobsen's chiral salen Co(ii) (salen = N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine) compound is attained by dinuclear chiral salen Co(iii)-OTf complex formation with yttrium triflate. The yttrium metal not only displays a promoting effect on electron transfer, but also assists in forming two stereocentres of a Lewis acid complex with Co(iii)-OTf. We found that the binuclear Co-complex significantly enhanced reactivity and enantioselectivity in the hydrolytic kinetic resolution of terminal epoxides compared to its analogous monomer and kinetic data are also consistent with these results.
- Patel, Deepak,Kurrey, Ganesh Ram,Shinde, Sandip S.,Kumar, Pradeep,Kim, Geon-Joong,Thakur, Santosh Singh
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p. 82699 - 82703
(2015/10/19)
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- Total synthesis of the proposed structures of eushearilide
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Total synthesis of (3R,16Z,20E,23S)- and (3R,16Z,20E,23R)-eushearilide was accomplished in 15 steps, respectively. Using either enantiomer of one of the four building blocks to assemble the phosphonium salt for the latter Wittig reaction, two diastereomers of eushearilide were prepared. Shiina macrolactonization (2-methyl-6-nitrobenzoic anhydride) was a key step in production of the 24-membered lactone in high yield.
- Yamauchi, Takayasu,Takidaira, Jun-Ichi,Okamoto, Kenya,Sugiura, Takaya,Horikoshi, Hiroki,Kudo, Shintaro,Sasaki, Shigeru,Mizushima, Noriko,Higashiyama, Kimio
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p. 1175 - 1189
(2014/01/17)
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- Asymmetric hydrolytic kinetic resolution with recyclable polymeric Co(iii)-salen complexes: A practical strategy in the preparation of (S)-metoprolol, (S)-toliprolol and (S)-alprenolol: Computational rationale for enantioselectivity
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A series of chiral polymeric Co(iii)-salen complexes based on a number of achiral and chiral linkers were synthesized and their catalytic performances were assessed in the asymmetric hydrolytic kinetic resolution of terminal epoxides. The effects of the linker were judiciously studied and it was found that in the case of the chiral BINOL-based polymeric salen complex 1, there was an enrichment in catalyst reactivity and enantioselectivity of the unreacted epoxide, particularly in the case of short as well as long chain aliphatic epoxides. Good isolated yields of the unreacted epoxide (up to 46% compared to 50% theoretical yield) along with high enantioselectivity (up to 99%) were obtained in most cases using catalyst 1. Further studies showed that catalyst 1 could retain its catalytic activity for six cycles under the present reaction conditions without any significant loss in activity or enantioselectivity. To show the practical applicability of the above synthesized catalyst we have synthesised some potent chiral β-blockers in moderate yield and high enantioselectivity using complex 1. The DFT (M06-L/6-31+G??//ONIOM(B3LYP/6-31G?:STO-3G)) calculations revealed that the chiral BINOL linker influences the enantioselectivity achieved with Co(iii)-salen complexes. Further, the transition state calculations show that the R-BINOL linker with the (S,S)-Co(iii)-salen complex is energetically preferred over the corresponding S-BINOL linker with the (S,S)-Co(iii)-salen complex for the HKR of 1,2-epoxyhexane. The role of non-covalent C-H?π interactions and steric effects has been discussed to control the HKR reaction of 1,2-epoxyhexane.
- Roy, Tamal,Barik, Sunirmal,Kumar, Manish,Kureshy, Rukhsana I.,Ganguly, Bishwajit,Khan, Noor-Ul H.,Abdi, Sayed H. R.,Bajaj, Hari C.
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p. 3899 - 3908
(2015/02/19)
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- Tailoring the window sizes to control the local concentration and activity of (salen)Co catalysts in plugged nanochannels of SBA-15 materials
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Ship shape! Chiral (salen)CoIII complexes (spheres) inside plugged nanochannels of SBA-15 materials is achieved using a ship-in-a-bottle synthesis technique. The local concentration of the metal complexes and the catalytic activity (such as the hydrolytic kinetic resolution of 1,2-epoxyalkanes; see scheme) showed a strong dependence on the size of the window. Copyright
- Shakeri, Mozaffar,Klein Gebbink, Robertus J. M.,De Jongh, Petra E.,De Jong, Krijn P.
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p. 10854 - 10857
(2013/10/22)
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- Stereoselective total synthesis of 4-ketoclonostachydiol
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An efficient stereoselective total synthesis of the bioactive 14-membered natural macrocyclic bislactone 4-ketoclonostachydiol is described. The strategy involves a Jacobsen's hydrolytic kinetic resolution (HKR), epoxide opening, MacMillan α-hydroxylation, Horner-Wadsworth-Emmons olefination, a Grignard reaction, and Hoveyda-Grubbs-II-catalyzed ring-closing metathesis (RCM) as key steps.
- Rajaram, Singanaboina,Ramulu, Udugu,Ramesh, Dasari,Prabhakar, Peddikotla,Venkateswarlu, Yenamandra
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p. 2115 - 2123
(2013/12/04)
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- Immobilized Aspergillus niger epoxide hydrolases: Cost-effective biocatalysts for the prepation of enantiopure styrene oxide, propylene oxide and epichlorohydrin
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This study aimed to prepare robust immobilized epoxide hydrolase (EH) preparations for asymmetric hydrolysis of racemic epoxides such as styrene oxide, propylene oxide and epichlorohydrin. For this purpose, Aspergillus niger EH was immobilized onto Lewatit VP OC 1600 support by adsorption, modified Florisil and Eupergit C supports by covalently. The suitability of the supports was examined for protein binding capacity and rate of racemic styrene oxide hydrolysis. The protein-activity recovery yields were 75-85%, 82-78% and 90-75%, respectively for EH immobilized onto Lewatit VP OC 1600, modified Florisil and Eupergit C supports. All A. niger EH preparations catalyzed preferentially hydrolysis of (R)-epoxides. Although enantiomeric excess values of all the tested epoxides were 99%, the highest enantiopure epoxide yields were obtained as 48% for (S)-styrene oxide by the immobilized EHs onto modified Florisil and Eupergit C. The highest diol yield was obtained as 78% for 3-chloro-1,2-propanediol, however, its enantiomeric excess value was 28.2%. Enantioselectivity of A. niger EH was improved with the preparation of mentioned immobilized forms. The highest enantioselectivity value was obtained as 95 toward styrene oxide by A. niger EH immobilized onto modified Florisil . The results of reusability studies show that the immobilized EH preparations offer feasible potentials for the preparation of enantiopure epoxides than that of free form.
- Yildirim, Deniz,Tuekel, S. Seyhan,Alptekin, Oezlem,Alagoez, Dilek
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- Asymmetric hydrolytic kinetic resolution with recyclable macrocyclic CoIII-salen complexes: A practical strategy in the preparation of (R)-mexiletine and (S)-propranolol
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A chiral cobalt(III) complex (1 e) was synthesized by the interaction of cobalt(II) acetate and ferrocenium hexafluorophosphate with a chiral dinuclear macrocyclic salen ligand that was derived from 1R,2R-(-)-1,2-diaminocyclohexane with trigol bis-aldehyde. A variety of epoxides and glycidyl ethers were suitable substrates for the reaction with water in the presence of chiral macrocyclic salen complex 1 e at room temperature to afford chiral epoxides and diols by hydrolytic kinetic resolution (HKR). Excellent yields (47 % with respect to the epoxides, 53 % with respect to the diols) and high enantioselectivity (ee>99 % for the epoxides, up to 96 % for the diols) were achieved in 2.5-16 h. The CoIII macrocyclic salen complex (1 e) maintained its performance on a multigram scale and was expediently recycled a number of times. We further extended our study of chiral epoxides that were synthesized by using HKR to the synthesis of chiral drug molecules (R)-mexiletine and (S)-propranolol.
- Sadhukhan, Arghya,Khan, Noor-Ul H.,Roy, Tamal,Kureshy, Rukhsana I.,Abdi, Sayed H. R.,Bajaj, Hari C.
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supporting information; experimental part
p. 5256 - 5260
(2012/06/01)
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- Asymmetric ring opening of terminal epoxides via kinetic resolution catalyzed by chiral (salen)Co mixture
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The highly enantioselective hydrolytic kinetic resolution (HKR) of racemic terminal epoxides by bimetallic chiral (salen)Co and (salen)Co(III)-OAc mixture provides a simple and effective method for the synthesis of enantiomerically enriched terminal epoxides (ee > 99%) and diols. At the equimolar amounts of bimetallic chiral (salen)Co and (salen)Co(II)-OAc, the catalytic activity increases more than two times in comparison with (salen)Co(III)-OAc used alone. The mixed catalytic system can be recycled and reused. No significant loss of catalytic activity was observed after three runs.
- Jiang, Chengjun
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experimental part
p. 691 - 696
(2011/11/30)
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- Stereoseletive total synthesis of 11-α- and 11-β- methoxycurvularins
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Total synthesis of 11-α-methoxycurvularin and 11-β- methoxycurvularin has been accomplished in a highly stereoselective manner by utilizing Jacobsen hydrolytic kinetic resolution, Maruoka asymmetric allylation and intramolecular Friedel-Crafts acylation as key steps. Georg Thieme Verlag Stuttgart.
- Yadav,Raju,Ravindar,Reddy, B.V. Subba
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experimental part
p. 797 - 802
(2010/10/04)
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- ISOSELECTIVE POLYMERIZATION OF EPOXIDES
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The present invention provides novel bimetallic complexes and methods of using the same in the isoselective polymerization of epoxides. The invention also provides methods of kinetic resolution of epoxides. The invention further provides polyethers with high enantiomeric excess that are useful in applications ranging from consumer goods to materials.
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Page/Page column 68-69
(2009/04/25)
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- NEW CHIRAL SALEN CATALYSTS AND METHODS FOR THE PREPARATION OF CHIRAL COMPOUNDS FROM RACEMIC EPOXIDES BY USING THEM
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The present invention relates to new chiral salen catalysts and the preparation method of chiral compounds from racemic epoxides using the same. More specifically, it relates to new chiral salen catalysts that have high catalytic activity due to new molecular structures and have no or little racemization of the generated target chiral compounds even after the reaction is completed and can be also reused without catalyst regeneration treatment, and its economical preparation method to mass manufacture chiral compounds of high optical purity, which can be used as raw materials for chiral food additives, chiral drugs, or chiral crop protection agents, etc., using the new chiral salen catalysts.
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Page/Page column 39
(2009/01/24)
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- RCM mediated synthesis of macrosphelides I and G
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The total synthesis of 16-membered macrolides, macraosphelides I and G, has been achieved starting from ethyl-(S)-lactate and (S)-malic acid. A combination of Jacobsen's hydrolytic kinetic resolution and Sharpless epoxidation is used for the creation of two stereogenic centres, while Yamaguchi esterification and ring-closing metathesis strategies were used for the construction of the lactone ring.
- Sharma, Gangavaram V.M.,Veera Babu, Kagita
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p. 2175 - 2184
(2008/02/11)
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- Carbonylative ring opening of terminal epoxides at atmospheric pressure
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(Chemical Equation Presented) The carbonylative opening of terminal epoxides under mild conditions has been developed using Co2-(CO) 8 as the catalyst. Under 1 atm of carbon monoxide and at room temperature in methanol, propylene oxide is converted to methyl 3-hydroxybutanoate in up to 89% yield. This transformation is general for many terminal epoxides bearing alkyl, alkenyl, aryl, alkoxy, chloromethyl, phthalimido, and acetal functional groups. The opening takes place without epimerization at the secondary stereocenter.
- Denmark, Scott E.,Ahmad, Moballigh
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p. 9630 - 9634
(2008/03/17)
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- "Cassette" in situ enzymatic screening identifies complementary chiral scaffolds for hydrolytic kinetic resolution across a range of epoxides
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(Figure Presented) Put the cassette in: An in situ enzymatic screen can give real-time estimates of the sense and magnitude of enantioselectivity across more than one substrate. Screening identified CoIII-salen catalysts with β-pinene- and α-naphthylalanine-derived chiral scaffolds with broad, yet complementary, substrate specificities. ADH = alcohol dehydrogenase, HL = horse liver, LK = Lactobacillus kefir, salen = (salicylidene) ethylenediamine.
- Dey, Sangeeta,Powell, Douglas R.,Hu, Chunhua,Berkowitz, David B.
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p. 7010 - 7014
(2008/09/17)
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- A new dinuclear chiral salen complexes for asymmetric ring opening and closing reactions: Synthesis of valuable chiral intermediates
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A new dinuclear chiral Co(salen) complexes bearing group 13 metals have been synthesized and characterized. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity for the asymmetric ring opening of epoxides with H2O, chloride ions and carboxylic acids and consequently provide enantiomerically enriched terminal epoxides (>99% ee). It also catalyzes the asymmetric cyclization of ring opened product, to prepare optically pure terminal epoxides in one step. The homogeneous dinuclear chiral Co(salen) have been covalently immobilized on MCM-41. The potential benefits of heterogenization include facilitation of catalyst separation and recyclability requiring very simple techniques. The system described is very efficient.
- Thakur, Santosh Singh,Chen, Shu-Wei,Li, Wenji,Shin, Chang-Kyo,Kim, Seong-Jin,Koo, Yoon-Mo,Kim, Geon-Joong
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p. 1862 - 1872
(2007/10/03)
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- Catalytic asymmetric addition of carbon dioxide to propylene oxide with unprecedented enantioselectivity
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New chiral catalyst systems were developed for the reaction of carbon dioxide with propylene oxide (PO) at atmospheric pressure to generate enantiomerically enriched propylene carbonate (PC). The best selectivity was achieved with a CoIII(salen)-trifluoroacetyl complex and bis-(triphenylphosphoranylidene)ammonium fluoride (PPN+F-) as catalysts, affording PC in 40% yield and 83% ee (selectivity factor = 19). In addition, PC was prepared for the first time by kinetic resolution of PO with tetrabutylammonium methyl carbonate (TBAMC, nBu4N +-OOCOMe). With TBAMC as "activated CO2", up to 71% ee was obtained.
- Berkessel, Albrecht,Brandenburg, Marc
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p. 4401 - 4404
(2007/10/03)
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- A simple and efficient approach to 1,3-polyols: Application to the synthesis of cryptocarya diacetate
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A highly enantio- and stereoselective synthetic strategy for both syn-and anti-1,3-polyols has been developed. The sequence involves iterative Jacobsen's hydrolytic kinetic resolution (HKR), diastereoselective iodine-induced electrophilic cyclization, and ring-closing metathesis (RCM). This protocol has subsequently been utilized for the synthesis of cryptocarya diacetate, a natural product with broad range of biological activity.
- Kumar, Pradeep,Gupta, Priti,Vasudeva Naidu
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p. 1397 - 1402
(2008/01/27)
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- Asymmetric epoxidation of terminal alkenes with hydrogen peroxide catalyzed by pentafluorophenyl PtII complexes
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Easily accessible chiral PtII complexes 1 allow highly enantioselective and completely regioselective asymmetric epoxidation of terminal alkenes with hydrogen peroxide. Copyright
- Colladon, Marco,Scarso, Alessandro,Sgarbossa, Paolo,Michelin, Rino A.,Strukul, Giorgio
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p. 14006 - 14007
(2007/10/03)
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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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- Synthesis of optically active 2-hydroxy monoesters via-kinetic resolution and asymmetric cyclization catalyzed by heterometallic chiral (salen) Co complex
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The binuclear chiral (salen) Co complexes bearing Lewis acids of Al and Ga catalyze regio- and enantioselective ring opening of terminal epoxides with carboxylic acids. The ring opened product of epichlorohydrin with carboxylic acids followed by cyclization step in the presence of catalyst and base represent straightforward, efficient methods for the synthesis of enatiomerically enriched (>99% ee) valuable terminal epoxides. Strong synergistic effects of different Lewis acid of Co-Al and Co-Ga were exhibited in the catalytic process.
- Li, Wenji,Thakur, Santosh Singh,Chen, Shu-Wei,Shin, Chang-Kyo,Kawthekar, Rahul B.,Kim, Geon-Joong
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p. 3453 - 3457
(2007/10/03)
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- Highly reactive and enantioselective kinetic resolution of terminal epoxides with H2O and HCl catalyzed by new chiral (salen)Co complex linked with Al
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The asymmetric hydrolytic kinetic resolution (HKR) of racemic terminal epoxides by new easily synthesized dimeric chiral (salen)Co bearing Al, provides a practical and straightforward method for the synthesis of enantiomerically enriched terminal epoxides (>99% ee) and diols. An inorganic acid, HCl is applied first time for the asymmetric ring opening reaction of terminal epoxides. Reactions are conveniently carried out at room temperature under an air atmosphere.
- Thakur, Santosh Singh,Li, Wenji,Kim, Seong-Jin,Kim, Geon-Joong
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p. 2263 - 2266
(2007/10/03)
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- Alternating copolymerization of CO2 and propylene oxide catalyzed by CoIII(salen)/Lewis base
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The use of CoIII(salen)/Lewis base catalyst system for copolymerization of CO2 and propylene oxide was analyzed. The ratio of catalyst to Lewis base cocatalyst influenced the TOF. The use of Lewis base cocatalyst enables high catalytic activity at low CO2 pressure and affords superior enantioselectivity. The results show that the use of cocatalyst produced a highly alternating monodisperse polycarbonate product without concomitant cyclic carbonate production.
- Paddock, Robert L.,Nguyen, SonBinh T.
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p. 6251 - 6253
(2008/02/02)
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- 4-ANILINO-QUINAZOLINE DERIVATIVES AS ANTIPROLIFERATIVE AGENTS
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A quinazoline derivative of the formula (I): wherein the substituents are as defined in the text for use in the production of an anti proliferative effect which effect is produced alone or in part by inhibiting erbB2 receptor tyrosine kinase in a warm blooded animal such as man.
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Page/Page column 111
(2008/06/13)
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- AlEt3-promoted eliminative ring-opening of β-hydroxy epoxides: Highly stereoselective synthesis of terminal α-hydroxy olefins
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AlEt3-promoted eliminative ring-opening of β-epoxy alcohols leading to α-hydroxy olefins is reported. This eliminative ring-opening reaction is shown to be highly stereoselective, thus providing an alternative asymmetric synthesis for α-hydroxy olefins.
- Wang, Fei,Wang, Shao Hua,Tu, Yong Qiang,Ren, Shi Kuo
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p. 2189 - 2193
(2007/10/03)
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- A practical oligomeric [(salen)Co] catalyst for asymmetric epoxide ring-opening reactions
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Prepared by a high yield, chromatography-free route, "oligosalen" exists as a mixture of dimer, trimer, and tetramer (see picture). Derived catalyst systems display remarkable activity and selectivity in the asymmetric ring-opening of epoxides, with turnover numbers exceeding 100000 in some cases.
- Ready, Joseph M.,Jacobsen, Eric N.
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p. 1374 - 1377
(2007/10/03)
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- Highly selective hydrolytic kinetic resolution of terminal epoxides catalyzed by chiral (salen)CoIII complexes. Practical synthesis of enantioenriched terminal epoxides and 1,2-diols
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The hydrolytic kinetic resolution (HKR) of terminal epoxides catalyzed by chiral (salen)CoIII complex 1·OAc affords both recovered unreacted epoxide and 1,2-diol product in highly enantioenriched form. As such, the HKR provides general access to useful, highly enantioenriched chiral building blocks that are otherwise difficult to access, from inexpensive racemic materials. The reaction has several appealing features from a practical standpoint, including the use of H2O as a reactant and low loadings (0.2-2.0 mol %) of a recyclable, commercially available catalyst. In addition, the HKR displays extraordinary scope, as a wide assortment of sterically and electronically varied epoxides can be resolved to ≥ 99% ee. The corresponding 1,2-diols were produced in good-to-high enantiomeric excess using 0.45 equiv of H2O. Useful and general protocols are provided for the isolation of highly enantioenriched epoxides and diols, as well as for catalyst recovery and recycling. Selectivity factors (krel) were determined for the HKR reactions by measuring the product ee at ca. 20% conversion. In nearly all cases, krel values for the HKR exceed 50, and in several cases are well in excess of 200.
- Schaus, Scott E.,Brandes, Bridget D.,Larrow, Jay F.,Tokunaga, Makoto,Hansen, Karl B.,Gould, Alexandra E.,Furrow, Michael E.,Jacobsen, Eric N.
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p. 1307 - 1315
(2007/10/03)
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- Synthesis and absolute configuration of two defensive alkaloids from the Mexican bean beetle, Epilachna varivestis
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Syntheses of (2S,12'R)-2-(12'-aminotridecyl)-pyrrolidine (1) and (28,12'R)-1-(2'-hydroxyethyl)-2-(12'-aminotridecyl)-pyrrolidine (2), two defensive alkaloids recently isolated from the Mexican bean beetle, Epilachna varivestis, are described. By a comparison of 1H NMR data of MTPA derivatives of natural alkaloid 2 with those of the synthetic standard, we confirm the (2S,12'R) configuration previously suggested for this alkaloid. Further support of these assignments was provided by the synthesis and 1H NMR investigation of(2S,12'S)-1, (2S,12'S)-2, and their MTPA derivatives.
- Shi, Xiongwei,Attygalle, Athula B.,Meinwald, Jerrold
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p. 6479 - 6482
(2007/10/03)
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- Enantioselective hydrolysis of aryl, alicyclic and aliphatic epoxides by Rhodotorula glutinis
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Enantioselective epoxide hydrolysis by yeasts has been demonstrated for the hydrolysis of several aryl, alicyclic and aliphatic epoxides by a strain of Rhodotorula glutinis. High enantioselectivity was obtained in the hydrolysis of methyl substituted aryl and aliphatic epoxides whereas selectivity towards terminal epoxides in all cases was lower. Homochiral vicinal diols were formed from several methyl substituted epoxides and also from meso epoxides. Kinetic resolution of trans-1-phenyl-1,2-epoxypropane was studied in more detail.
- Weijers, Carel A. G. M.
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p. 639 - 647
(2007/10/03)
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- Pigments of fungi. Part 41. Synthesis of (S)-(+)- and (+/-)-dermolactone; stereochemistry of dermocactone from the Australian fungus Dermocybe sanguinea (Wulf. ex Fr.) Wuensche sensu Cleland
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(S)-(+)-Dermolactone 3 has been synthesised in monochiral form beginning with ethyl (S)-lactate, the tetracyclic nucleus being assembled by way of a regiospecific cycloaddition between the known chloronaphthoquinone 15 and the novel, highly functionalised chiral butadiene 5.Isochiral dermolactone 3 + 4 is prepared in the same way from (+/-)-5.Dermolactone, as it occurs naturally, is shown by 1H NMR shift experimants on the corresponding permethyl ethers 25 and 27, using , to consist of an anisochiral mixture of the (S)-(+)- and (R)-(-)-enantiomers 3 and 4, respectively, in which the former predominates in the ratio of 1.8:1 (28.6percent ee).
- Cotterill, Ann S.,Gill, Melvyn,Milanovic, Nives M.
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p. 1215 - 1224
(2007/10/02)
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- (S)-(-)-ethyl lactate as a convenient precursor for synthesis of chiral liquid crystals
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A strategy is presented for synthesis of optically active precursors derived from (S)-(-)-ethyl lactate for use in synthesis of chiral liquid crystals.
- Merlo,Gallardo
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p. 2159 - 2169
(2007/10/02)
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- Lipase Catalyzed Resolution of 1-t-Butylthio-2-alkanols: Enzyme Mediated Routes to Enantiomerically Pure 1,2-Epoxyalkanes and 2-Alkanols
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A series of 1-t-butylthio-2-alkanols (R)- and (S)-1-5 were prepared via lipase catalyzed resolution of the corresponding chloroacetates (+/-)-1a-5a and further converted into the optically pure alkyloxiranes (R)-6-8 and 2-alkanols (R)-14-15
- Goergens, Ulrich,Schneider, Manfred P.
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p. 1149 - 1152
(2007/10/02)
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- Oxygen Donation by an Intermadiate in the Reaction of 3CF2 with O2
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Reaction of 3CF2, produced by reaction of arc-generated carbon atoms with CF3, with oxygen in the presence of alkenes oxygenates to epoxides, which are formed stereospecifically, and carbonyl compounds.The reaction is postulated to involve the intermediacy of difluorodioxirane, which transfers oxygen stereospecifically to the alkene.Ab inito calculations demonstrate that the difluorodioxirane is more stable than the corresponding carbonyl oxide to the dioxirane should be rapid.The results of these calculations are compared to those on the parent CH2O2 system.Reaction of carbon atoms with oxigen and alkenes in the absence of CF3 gives nonstereospecific epoxidation presumably through the intermediacy of O atoms.
- Rahman, M.,McKee, Michael L.,Shevlin, Philip B.,Sztyrbicka, Renata
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p. 4002 - 4007
(2007/10/02)
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- SYNTHESIS OF THE ENANTIOMERS OF CIS-2-METHYL-5-HEXANOLIDE, THE MAJOR COMPONENT OF THE SEX PHEROMONE OF THE CARPENTER BEE
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(2R,5S)-2-Methyl-5-hexanolide and its antipode were synthesized in highly optically pure state (98-99percent e.e.) starting from ethyl (S)-lactate and the enantiomers of methyl β-hydroxyisobutyrate.The specific rotations of our samples were D +/- 91.0 -93.5 deg (CHCl3), while the reported values of the samples prepared by resolution or asymmetric synthesis were +/- 64.5-65.6 deg.
- Mori, Kenji,Senda, Shuji
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p. 541 - 546
(2007/10/02)
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- ASYMMETRIC HALOGENATION OF CAMPHOR-10-SULFONIC ACID DERIVED ESTERS: AN EFFICIENT NEW ROUTE TO ENANTIOMERICALLY PURE HALOHYDRINS AND EPOXIDES.
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Successive treatment of chiral esters 1 with LDA/Me3SiCl and NBS or NCS gave crystalline α-haloesters 3 which furnished halohydrins 4 and terminal epoxides 5 in high e.e..
- Oppolzer, Wolfgang,Dudfield, Philip
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p. 5037 - 5040
(2007/10/02)
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- Diethoxytriphenylphosphorane: A Mild, Regioselective Cyclodehydrating Reagent for Conversion of Diols to Cyclic Ethers. Stereochemistry, Synthetic Utility, and Scope
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Diethoxytriphenylphosphorane, Ph3P(OEt)2, prepared by reaction of triphenylphosphine and diethyl peroxide, is a "hydrolytically active" dioxyphosphorane which promotes mild cyclodehydration (40-110 deg C) of diols to cyclic ethers in neutral media.The regioselectivity in the closure of (S)-(+)-propane-1,2-diol and (R)-(-)-pentane-1,4-diol with Ph3P(OEt)2 is high (81-82 percent) while the cyclodehydration of (S)-(+)-phenylethane-1,2-diol gives racemized (+/-)-styrene oxide.Simple 1,2-, 1,4-, and 1,5-diols afford good yields of the cyclic ethers but 1,3-propanediol and 1,6-hexanediol give mainly 3-ethoxy-1-propanol and 6-ethoxy-1-hexanol, respectively with Ph3P(OEt)2.Tri- and tetra-substituted 1,2-diols afford the relatively stable 1,3,2-dioxaphospholanes (or ?-dioxyphosphoranes) in the presence of Ph3P(OEt)2, and, depending on conditions, the 1,3,2-dioxaphospholanes are selectively converted to epoxides, ketones or allylic alcohols.The carbonyl compounds arise from 1,2-hydride and 1,2-methyl migrations; the allylic alcohols are derived from thermolytic eliminations. trans-1,2-Cyclohexanediols afford essentially quantitative yields (>95 percent) of the cyclohexene oxides while cis-1,2-cyclohexanediol gives the stable 1,3,2-dioxaphospholane with Ph3P(OEt)2 which decomposes under thermal conditions to cyclohexanone (90 percent).Ph3P(OEt)2 is extremely useful for conversion of "sensitive" 1,2-diols to acidic and /or thermally labile epoxides as demonstrated by the quantitative conversion of 9,10-dihydro-trans-9,10-phenanthrenediol to 9,10-dihydrophenanthrene oxide and 2α,10-pinanediol to 2α,10-epoxypinane.
- Robinson, Philip L.,Barry, Carey N.,Kelly, Jeffery W.,Evans, Slayton A.
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p. 5210 - 5219
(2007/10/02)
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- Preparative Production of Optically Active Esters and Alcohols Using Esterase-Catalyzed Stereospecific Transesterification in Organic Media
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A novel enzymatic approach to the production of optically active alcohols and esters from racemates is developed.It involves the use of esterase catalyzed transesterifications carried out in biphasic aqueous-organic mixtures.Water-insoluble substrates constitute the organic phase, while the enzyme is located in the aqueous phase.Since the fraction of the latter phase can be made very low, such an arrangement solves the problem of both the competition of an alcohol (the nucleophile) with water in the enzymatic reaction and poor solubility of most organic esters and alcohols in water.By use of porous supports (Sepharose or Chromosorb) filled with aqueous solutions of hog liver carboxyl esterase as a stereoselective catalyst and methyl propionate as a matrix ester, the following optically active alcohols and their propionic esters were produced on a preparative scale: 3-methoxy-1-butanol, 3-methyl-1-pentanol, 3,7-dimethyl-1-octanol, and β-citronellol.To overcome a rather narrow substrate specificity of hog liver carboxyl esterase, a nonspecific lipase from yeast (Candida cylindracea) also was employed as a stereoselective transesterification catalyst.Using an aqueous solution of this enzyme confined to the pores of Chromosorb and tributyrin as a matrix ester, we have prepared gram amounts of the following optically active alcohols and their butyric esters: 2-butanol, sec-phenethyl alcohol, 2-octanol, 1-chloro-2-propanol and 2,3-dichloro-1-propanol (subsequently nonenzymatically converted to optically active propylene oxide and epichlorohydrin, respectively), 6-methyl-5-hepten-2-ol, and 1,2-butanediol.
- Cambou, Bernard,Klibanov, Alexander M.
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p. 2687 - 2692
(2007/10/02)
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- SYNTHESIS OF ALL OF THE FOUR ENERGETICALLY POSSIBLE STEREOISOMERS OF 7-ETHYL-2-METHYL-1,6-DIOXASPIRODECANE; A PHEROMONE PRODUCED BY BEES PARAVESPURA VULGARIS L. AND ANDRENA HAEMORRHOA F.
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All of the four energetically possible stereoisomers of 7-ethyl-2-methyl-1,6-dioxaspirodecane were synthesized starting from ethyl (S)-lactate and dimethyl (S)-malate or methyl (R)-β-hydroxy-valerate employing dianion alkylation as the key-step.
- Mori, Kenji,Ikunaka, Masaya
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p. 3471 - 3480
(2007/10/02)
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- THE REACTION OF DICHLOROCARBENE WITH β-ETHANOLAMINES. STEREOSPECIFIC SYNTHESIS OF EPOXIDES
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Optically pure β-ethanolamines were converted into epoxides in good yield and with high e.e. (>= 95percent) by reaction with dichlorocarbene.By this method α-aminoacids were successfully converted into synthetically useful epoxides.
- Castedo, Luis,Castro, Jose L.,Riguera, Ricardo
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p. 1205 - 1208
(2007/10/02)
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- Regioselective Cyclodehydration of Chiral Diols with Diethoxytriphenylphosphorane, Triphenylphosphine-Tetrachloromethane-Potassium Carbonate, and Triphenylphosphine-Diethyl Azodicarboxylate Reagents. A Comparative Study
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The regioselectivity of cyclodehydration of chiral diols has been examined with the reagents diethoxytriphenylphosphorane, triphenylphosphine-tetrachloromethane-potassium carbonate, and triphenylphosphine-diethyl azodicarboxylate. (S)-(+)-Propane-1,2-diol and (R)-(-)-pentane-1,4-diol afford 80-87percent retention of stereochemistry at the chiral carbon in the ether while (S)-(+)-phenylethane-1,2-diol affords essentially racemic styrene oxide with all three reagents.
- Robinson, Philip L.,Barry, Carey N.,Bass, S. Woody,Jarvis, Susan E.,Evans, Slayton A.
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p. 5396 - 5398
(2007/10/02)
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