- Synthesis of Epoxides from Alkyl Bromides and Alcohols with in Situ Generation of Dimethyl Sulfonium Ylide in DMSO Oxidations
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Direct conversion of the readily available alkyl bromides and alcohols to value-added epoxides using dimethyl sulfoxide (DMSO) under mild reaction conditions has been developed. Benzyl and allyl bromides, and activated and unactivated alcohols all proceeded smoothly to give epoxides in high to excellent yield. Dimethyl sulfide, generated by DMSO oxidations, was in situ elaborated to form the substituted dimethyl sulfonium ylide species that participates in the Corey-Chaykovsky epoxidation in a domino and one-pot fashion, respectively.
- Zhang, Zhi-Wei,Li, Hai-Bo,Li, Jin,Wang, Cui-Cui,Feng, Juan,Yang, Yi-Hua,Liu, Shouxin
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p. 537 - 547
(2020/01/02)
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- Method used for direct synthesis of epoxy compounds from alcohol
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The invention discloses a method used for direct synthesis of an epoxy compounds from an alcohol. According to the method, an alcohol is taken as a raw material, Swern oxidation is adopted to synthesize an aldehyde, a bromo-hydrocarbon and an alkali are added into the aldehyde directly to construct epoxy functional groups, and generate the epoxy compound. According to the method, one-pot method is adopted to realize direct epoxidation of the alcohol, the synthesis route is simple, the preparation process is easy to control, no catalyst is needed in the process, substrate suitable range is wide, reagents are cheap and easily available, preparation conditions are mild, reaction yield is high, and the method is suitable for synthesis of epoxy compounds.
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Paragraph 0180-0187
(2019/10/08)
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- Chiral Macrocyclic Organocatalysts for Kinetic Resolution of Disubstituted Epoxides with Carbon Dioxide
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Among chiral macrocycles 1 synthesized, 1m with the 3,5-bis(trifluoromethyl)phenylethynyl group was the best organocatalyst for the enantioselective synthesis of cyclic carbonates from disubstituted or monosubstituted epoxides and CO2. The X-ray crystal structure of 1m revealed a well-defined chiral cavity with multiple hydrogen-bonding sites that is suitable for the enantioselective activation of epoxides. A catalytic cycle proposed was supported by DFT calculations.
- Ema, Tadashi,Yokoyama, Maki,Watanabe, Sagiri,Sasaki, Sota,Ota, Hiromi,Takaishi, Kazuto
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supporting information
p. 4070 - 4073
(2017/08/15)
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- Benzylic Ammonium Ylide Mediated Epoxidations
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A high yielding synthesis of stilbene oxides using ammonium ylides has been developed. It turned out that the amine leaving group plays a crucial role as trimethylamine gives higher yields than DABCO or quinuclidine. The amine group also influences the diastereoselectivity, and detailed DFT calculations to understand the key parameters of these reactions have been carried out.
- Roiser, Lukas,Robiette, Rapha?l,Waser, Mario
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supporting information
p. 1963 - 1968
(2016/08/10)
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- Catalytic, regioselective, and green methods for rearrangement of 1,2-diaryl epoxides to carbonyl compounds employing metallic triflates, Br?nsted-acidic ionic liquids (ILs), and IL/microwave; Experimental and computational substituent effect study on aryl versus hydrogen migration
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The Lewis-acid catalyzed rearrangement of parent trans-stilbene oxide 1 was studied with M(OTf)3/DCM and M(OTf)3/[BMIM][BF 4] (M = Bi, Al, Ga, Sc, and Yb; [BMIM] = butylmethylimidazolium) and Zn(NTf2)2, and with Bi(OTf)3/[BMIM][X] (X = NTf2, OTf, PF6, and BF4), employing 5 mol% of catalyst. Selective formation of 2,2-dipheylacetaldehyde 2 (phenyl migration product) was observed in all cases, with Bi(OTf)3 proving most efficient. The rearrangement of 1 was also effected in [BMIM][X] (X = NTf 2, OTf, PF6, and BF4) without an added catalyst under microwave MW irradiation, and X = PF6 gave the highest yield and selectivity. Efficient and selective rearrangement of 1-2 was also observed with 0.1-0.3 equiv. of [BMIM(SO3H)][OTf] in DCM and in [BMIM][X]. A substituent effect study was performed with a series of singly substituted 1,2-diphenyl oxiranes (with X = OMe, Me, F, CN, and NO2) with 5 mol% Bi(OTf)3 in DCM and in [BMIM][NTf2]. Notable formation of ketones was observed with the NO2 and CN derivatives. Competing formation of ketones was also observed in [BMIM][PF6] under MW and under Br?nsted acid catalysis with [BMIM(SO3H)][OTf] in DCM and in [BMIM][NTf2]. The aryl versus H migration was studied computationally by DFT and MP2 methods and by including solvation effects (IEFPCM).
- Jamalian, Arezu,Rathman, Benjamin,Borosky, Gabriela L.,Laali, Kenneth K.
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- Catalytic, regioselective, and green methods for rearrangement of 1,2-diaryl epoxides to carbonyl compounds employing metallic triflates, Br?nsted-acidic ionic liquids (ILs), and IL/microwave; experimental and computational substituent effect study on aryl versus hydrogen migration
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The Lewis-acid catalyzed rearrangement of parent trans-stilbene oxide 1 was studied with M(OTf)3/DCM and M(OTf)3/[BMIM][BF4] (M = Bi, Al, Ga, Sc, and Yb; [BMIM] = butylmethylimidazolium) and Zn(NTf2)2, and with Bi(OTf)3/[BMIM][X] (X = NTf2, OTf, PF6, and BF4), employing 5 mol% of catalyst. Selective formation of 2,2-dipheylacetaldehyde 2 (phenyl migration product) was observed in all cases, with Bi(OTf)3 proving most efficient. The rearrangement of 1 was also effected in [BMIM][X] (X = NTf2, OTf, PF6, and BF4) without an added catalyst under microwave MW irradiation, and X = PF6 gave the highest yield and selectivity. Efficient and selective rearrangement of 1-2 was also observed with 0.1-0.3equiv. of [BMIM(SO3H)][OTf] in DCM and in [BMIM][X]. A substituent effect study was performed with a series of singly substituted 1,2-diphenyl oxiranes (with X = OMe, Me, F, CN, and NO2) with 5mol% Bi(OTf)3 in DCM and in [BMIM][NTf2]. Notable formation of ketones was observed with the NO2 and CN derivatives. Competing formation of ketones was also observed in [BMIM][PF6] under MW and under Br?nsted acid catalysis with [BMIM(SO3H)][OTf] in DCM and in [BMIM][NTf2]. The aryl versus H migration was studied computationally by DFT and MP2 methods and by including solvation effects (IEFPCM).
- Jamalian, Arezu,Rathman, Benjamin,Borosky, Gabriela L.,Laali, Kenneth K.
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- Enantioselective synthesis of (thiolan-2-yl)diphenylmethanol and its application in asymmetric, catalytic sulfur ylide-mediated epoxidation
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This work describes an expeditious and efficient preparation of enantiopure (thiolan-2-yl)diphenylmethanol (2) featuring a double nucleophilic substitution and Shi epoxidation as key steps. One of the applications of its benzyl ether derivative to asymmetric sulfur ylide-mediated epoxidation with up to 92% ee (14 examples) was also demonstrated herein.
- Wu, Hsin-Yi,Chang, Chih-Wei,Chein, Rong-Jie
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p. 5788 - 5793
(2013/07/25)
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- Sequential- and tandem-oxidation-epoxidation reactions employing guanidine bases
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1,5,7-Triazabicyclo[4.4.0]dec-1-ene (TBD) and 7-methyl-1,5,7- triazabicyclo[4.4.0]dec-1-ene (MTBD) promote the efficient formation of sulfonium ylides from sulfonium salts in the Corey-Chaykovsky epoxidation of aldehydes and provide excellent yields of the corresponding epoxides. This reaction protocol can be further adapted to allow for the development of both sequential and tandem-oxidation-epoxidation protocols from aldehydes generated in situ by manganese dioxide (MnO2) or barium manganate (BaMnO 4) mediated oxidation reactions.
- Phillips, David J.,Kean, Joseline L.,Graham, Andrew E.
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p. 6196 - 6202
(2013/07/19)
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- A non-heme iron(III) complex with porphyrin-like properties that catalyzes asymmetric epoxidation
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In this report, we describe an iron(III) complex containing a carbazole-based tridentate ligand that catalyzes highly enantioselective asymmetric epoxidation of (E)-alkenes at room temperature. The non-heme iron(III) complex has a five-coordinated trigonal-bipyramidal structure, and its two-electron oxidized state has the similar electronic structure as that of iron porphyrins.
- Niwa, Takashi,Nakada, Masahisa
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p. 13538 - 13541
(2012/10/08)
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- A new chiral organosulfur catalyst for highly stereoselective synthesis of epoxides
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A new chrial organosulfide was synthesized through an unexpected Wagner-Meerwein rearrangement. This organosulfide could catalyze the epoxidation reaction of various aromatic aldehydes smoothly with benzyl bromide to give trans-diaryl epoxides in satisfactory yields (60-84%) with excellent diastereoselectivities (trans:cis=95:5-100:0) and good to excellent enantioselectivities (86-96% ee).
- Gui, Yuan,Li, Jian,Guo, Chang-Shan,Li, Xin-Liang,Lu, Zhi-Feng,Huang, Zhi-Zhen
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supporting information; experimental part
p. 2483 - 2487
(2009/09/08)
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- Delineation of the factors governing reactivity and selectivity in epoxide formation from ammonium ylides and aldehydes
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Diastereoselectivity in reactions of aryl-stabilised ammonium ylides are highly sensitive to the nature of the amine and the ylide substituent. DFT calculations are consistent with a mechanism in which reversibility in betaine formation [despite the high energy (and therefore instability) of ammonium ylides] is finely balanced due to the high barrier to ring closure. The Royal Society of Chemistry.
- Robiette, Raphael,Conza, Matteo,Aggarwal, Varinder K.
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p. 621 - 623
(2007/10/03)
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- Novel synthesis of α-arylnaphthalenes from diphenylacetaldehydes and 1,1-diphenylacetones
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A two-step synthesis of 1-amino-4-arylnaphthalene-2-carbonitriles from diphenylacetaldehydes and 1,1-diphenylacetones involves condensation of the carbonyl compounds with malonodinitrile and cyclization of the aryl-ylidenemalonodinitriles obtained in conc
- Kozik, Bart?omiej,Wilamowski, Jaros?aw,Góra, Maciej,Sepio?, Janusz J.
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p. 3435 - 3438
(2007/10/03)
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- New camphor-derived selenonium ylides: Enantioselective synthesis of chiral epoxides
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Optically pure selenonium salts 3 as the precursors of two new chiral selenonium ylides 4 can be synthesized stereoselectively from natural d-camphor in good yields. It is found that the reaction of the selenonium salt 3b, an aldehyde, and potassium tert-butoxide can take place smoothly in ?one-pot' via the formation of selenonium ylide 4b, to give chiral trans-diaryl epoxides 5 in good yields with good diastereoselectivities and enantioselectivities. CSIRO 2005.
- Li, Xin-Liang,Wang, Yi,Huang, Zhi-Zhen
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p. 749 - 752
(2007/10/03)
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- The highly trans-selective Darzens reaction via ammonium ylides
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The Darzens reaction using electron deficient p-substituted benzyltriethylammonium chlorides with aromatic aldehydes afforded 2,3-diaryl epoxides with trans selectivity (>99%) while the corresponding reaction with electron releasing p-substituted benzyltriethylammonium salts gave the epoxides as diastereomeric mixtures. Epoxide formation of p-trifluoromethylbenzylammonium salt, prepared from p-trifluoromethylbenzyl chloride and DABCO, afforded the corresponding 2,3-diaryl epoxide in high yield (>98%).
- Kimachi, Tetsutaro,Kinoshita, Hiroyo,Kusaka, Kumiko,Takeuchi, Yukiko,Aoe, Mai,Ju-Ichi, Motoharu
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p. 842 - 844
(2007/10/03)
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- Design of sulfides with a locked conformation as promoters of catalytic and asymmetric sulfonium ylide epoxidation
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A new generation of 2,5-dimethylthiolanes with a locked conformation was developed to promote the asymmetric addition of chiral sulfonium ylides to aldehydes. The novel chiral sulfur derivative 4 succeeded the synthesis of trans-stilbene oxide derivatives with enantiomeric ratios ranging from 95:5 to 98:2. This user-friendly organocatalytic process proved to be efficient with 20-10% of sulfide 4 in 1 or 2 days of reaction. An insight into the ylide intermediate conformation is given on the basis of a computational ab initio study.
- Davoust, Marion,Briere, Jean-Francois,Jaffres, Paul-Alain,Metzner, Patrick
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p. 4166 - 4169
(2007/10/03)
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- Epoxide Formation by Indirect Electroreductive Coupling between Aldehydes or Ketones and Activated gem-Dichloro Compounds
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Epoxides are prepared by indirect electroreductive coupling of carbonyl compounds (aldehydes or ketones) and activated gem-dichloro compounds. This process is more efficient with aryl ketones than with aryl aldehydes. Though yields are only moderate, this
- Oudeyer,Leonel,Paugam,Nedelec
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p. 389 - 400
(2007/10/03)
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- A new protocol for the in situ generation of aromatic, heteroaromatic, and unsaturated diazo compounds and its application in catalytic and asymmetric epoxidation of carbonyl compounds. Extensive studies to map out scope and limitations, and rationalization of diastereo- and enantioselectivities
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A variety of metalated tosylhydrazone salts derived from benzaldehyde have been prepared and were reacted with benzaldehyde in the presence of tetrahydrothiophene (THT) (20 mol %) and Rh2(OAc)4 (1 mol %) to give stilbene oxide. Of the lithium, sodium, and potassium salts tested, the sodium salt was found to give the highest yield and selectivity. This study was extended to a wide variety of aromatic, heteroaromatic, aliphatic, α,β-unsaturated, and acetylenic aldehydes and to ketones. On the whole, high yields of epoxides with moderate to very high diastereoselectivities were observed. A broad range of tosylhydrazone salts derived from aromatic, heteroaromatic, and α,β-unsaturated rated aldehydes was also examined using the same protocol in reactions with benzaldehyde, and again, good yields and high diastereoselectivities were observed in most cases. Thus, a general process for the in situ generation of diazo compounds from tosylhydrazone sodium salts has been established and applied in sulfur-ylide mediated epoxidation reactions. The chiral, camphor-derived, [2.2.1] bicyclic sulfide 7 was employed (at 5-20 mol % loading) to render the above processes asymmetric with a range of carbonyl compounds and tosylhydrazone sodium salts. Benzaldehyde tosylhydrazone sodium salt gave enantioselectivities of 91 ± 3% ee and high levels of diastereoselectivity with a range of aldehydes. However, tosylhydrazone salts derived from a range of carbonyl compounds gave more variable selectivities. Although those salts derived from electron-rich or neutral aldehydes gave high enantioselectivities, those derived from electron-deficient or hindered aromatic aldehydes gave somewhat reduced enantioselectivities. Using α,β-unsaturated hydrazones, chiral sulfide 7 gave epoxides with high diastereoselectivities, but only moderate yields were achieved (12-56%) with varying degrees of enantioselectivity. A study of solvent effects showed that, while the impact on enantioselectivity was small, the efficiency of diazo compound generation was influenced, and CH3CN and 1,4-dioxane emerged as the optimum solvents. A general rationalization of the factors that influence both relative and absolute stereochemistry for all of the different substrates is provided. Reversibility in formation of the betaine intermediate is an important issue in the control of diastereoselectivity. Hence, where low diastereocontrol was observed, the results have been rationalized in terms of the factors that contribute to the reduced reversion of the syn betaine back to the original starting materials. The enantioselectivity is governed by ylide conformation, facial selectivity in the ylide reaction, and, again, the degree of reversibility in betaine formation. From experimental evidence and calculations, it has been shown that sulfide 7 gives almost complete control of facial selectivity, and, hence, it is the ylide conformation and degree of reversibility that are responsible for the enantioselectivity observed. A simple test has been developed to ascertain whether the reduced enantioselectivity observed in particular cases is due to poor control in ylide conformation or due to partial reversibility in the formation of the betaine.
- Aggarwal, Varinder K.,Alonso, Emma,Bae, Imhyuck,Hynd, George,Lydon, Kevin M.,Palmer, Matthew J.,Patel, Mamta,Porcelloni, Marina,Richardson, Jeffery,Stenson, Rachel A.,Studley, John R.,Vasse, Jean-Luc,Winn, Caroline L.
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p. 10926 - 10940
(2007/10/03)
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- Generation of Sulfur Ylides from Sulfonium Salts and Their Reactions. Comparative Study of Electrochemical Reduction with the Base Method and Mechanism Elucidation by the MO Method
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The cathodic reduction of sulfonium salts in acetonitrile in the presence and absence of benzaldehyde was carried out. Results were compared with results of the base method. In the presence of benzaldehyde, the electrochemical reduction gave epoxides as a result of the Corey-Chaykovsky reaction, thus confirming ylide formation. The electrochemical reduction of sulfonium salts without benzaldehyde yielded rearrangement products in high yield. On the contrary, upon base treatment of sulfonium salts without benzaldehyde, symmetrical epoxides derived from the benzyl group of the sulfonium salt are obtained as main products as a result of the auto oxidation of the sulfur ylide. The reaction mechanisms were elucidated based on the results obtained by a semi-empirical molecular orbital method.
- Okazaki, Yuichi,Ando, Fumio,Koketsu, Jugo
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p. 2155 - 2165
(2007/10/03)
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- Highly stereoselective synthesis of trans-diaryl epoxides via semi-stabilised telluronium ylide
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Benzyldibutyltelluronium bromide can react with LDA to form benzyldibutyltelluronium ylide in situ, followed by the reaction with aromatic aldehydes, developed a novel method for the stereoselective synthesis of trans-diaryl epoxides.
- Wang, Lei,Huang, Zhizhen
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p. 305 - 306
(2007/10/03)
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- Process for the preparation of an oxirane, aziridine or cyclopropane
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A process for the preparation of an oxirane, aziridine or cyclopropane of formula (I), wherein X is oxygen, NR4or CHR5; R1is hydrogen, alkyl, aryl, heteroaromatic, heterocyclic or cycloalkyl; R2is hydrogen, alkyl, aryl, heteroaromatic, CO2R8, CHR14NHR13, heterocyclic or cycloalkyl; or R1and R2join together to form a cycloalkyl ring; R3and R10are, independently, hydrogen, alkyl, aryl, heteroaromatic, CO2R8, R83Sn, CONR8R9, trialkylsilyl or triarylsilyl; R4is an electron withdrawing group; R5is alkyl, cycloalkyl, aryl, heteroaromatic, SO2R8, SO3R8, COR8, CO2R8, CONR8R9, PO(R8)2, PO(OR8)2or CN; R8and R9are independently alkyl or aryl; and R13and R14are independently hydrogen, alkyl or aryl is provided. The process comprises degrading a compound of formula (II), (IIa), (IIb) or (IIc): wherein R3and R10are as defined above; Y is a cation; depending on the nature of Y, r is 1 or 2; and L is a suitable leaving group, to form a diazo compound. The diazo compound is reacted with a suitable transition metal catalyst, and the product thereof reacted with a sulphide of formula SR6R7, wherein R6and R7are independently alkyl, aryl or heteroaromatic, or R6and R7join together to form an optionally substituted ring which optionally includes an additional heteroatom. This product is then reacted with an aldehyde, ketone, imine or alkene.
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- Synthesis of epoxides from aldehydes and tosylhydrazone salts catalysed by triphenylarsine: Complete trans selectivity for all combinations of coupling partners
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Triphenylarsine catalyses the formation of epoxides from carbonyl compounds and tosylhydrazone salts. This convergent synthesis gives complete trans selectivity for all aldehyde and tosylhydrazone salt coupling partners.
- Aggarwal, Varinder K.,Patel, Mamta,Studley, John
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p. 1514 - 1515
(2007/10/03)
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- Asymmetric epoxidation of aldehydes catalyzed by new C2-symmetrical chiral sulfide
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Asymmetric synthesis of chiral epoxides from various aldehydes with benzyl bromide was investigated using new C2-symmetrical chiral sulfides, which were readily prepared from (R,R)-tartaric acid.
- Ishizaki, Miyuki,Hoshino, Osamu
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p. 1399 - 1402
(2007/10/03)
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- First chiral selenium ylides used for asymmetric conversion of aldehydes into epoxides
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Enantioenriched selenonium ylides have been generated by addition of benzyl bromide to C2 symmetric (2R,5R)2,5-dimethylselenolane in the presence of NaOH, and subsequently reacted with a variety of aldehydes to give oxiranes with excellent enantiomeric excesses (a catalytic version has been achieved); also, an aliphatic cyclic hypervalent dibromoselenurane structure has been demonstrated by X-ray analysis.
- Takada,Metzner,Philouze
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p. 2350 - 2351
(2007/10/03)
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- Catalytic asymmetric synthesis of epoxides from aldehydes using sulfur ylides with in situ generation of diazocompounds
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A practical, general, and convergent to epoxides with control of the relative and absolute stereochemistry has been achieved by generating the reactive intermediate (the diazo compound) in situ from tosylhydrazone salts (see scheme, PTC = phase-transfer catalyst, Ts = toluene-4-sulfonyl). High yields (58-82%), high d.r. (88:12-98:2), and high ee values (87-94%) have been obtained using a new class of stable chiral sulfides at low catalyst loading (5 mol%) and [Rh2(OAc)4] (0.5 mol%).
- Aggarwal, Varinder K.,Alonso, Emma,Hynd, George,Lydon, Kevin M.,Palmer, Matthew J.,Porcelloni, Marina,Studley, John R.
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p. 1430 - 1433
(2007/10/03)
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- Preparation of a novel, camphor-derived sulfide and its evaluation as a chiral auxiliary mediator in asymmetric epoxidation via the Corey-Chaykovsky reaction
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Sulfonium ylide-mediated asymmetric one-pot synthesis of optically active epoxides from aldehydes and bromides via the Corey-Chaykovsky reaction is described. The optically pure chiral sulfide was readily prepared from natural camphor via thiabutadiene Diels-Alder cycloaddition, followed by LiAlH4 reduction and hydrogenation of the cycloadduct.
- Saito, Takao,Akiba, Daisuke,Sakairi, Masao,Kanazawa, Shintaro
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- Synthesis of chiral epoxides from aldehydes using sulfur ylide derived from reduced product of bakers' yeast reduction
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Enantiomerically pure β-hydroxy ester derivatives possessing a sulfide group were obtained in the bakers' yeast reduction of the corresponding β- keto esters in the presence of a sulfur compound as an additive. Highly enantioselective synthesis of epoxides from aldehydes was achieved using sulfur ylide derived from chiral I β-hydroxy esters.
- Hayakawa, Ryuuichirou,Shimizu, Makoto
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p. 1328 - 1330
(2007/10/03)
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- Catalytic asymmetric epoxidation of aldehydes. Optimization, mechanism, and discovery of stereoelectronic control involving a combination of anomeric and cieplak effects in sulfur ylide epoxidations with chiral 1,3-oxathianes
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A range of 1,3-oxathianes based on camphorsulfonic acid have been prepared and tested in the catalytic asymmetric epoxidation of carbonyl compounds. It was found that the 1,3-oxathiane derived from acetaldehyde 5b gave the highest yield and enantioselectivity in the epoxidation process. The enantioselectivity was independent of the solvent and metal catalyst used (although yields were dependent on both). The optimum conditions were applied to a range of aldehydes, and good enantioselectivities and diastereoselectivities were observed. The origin of the enantioselectivity was probed, and in particular the role of the oxygen of the 1,3-oxathiane was investigated. Thus, the sulfur and carbon analogues of the camphorsulfonic acid based 1,3-oxathiane (derived from formaldehyde) were prepared (i.e., 1,3-dithiane and thiane analogues). With this series of analogues the steric effects are minimized so that the electronic effects can be investigated. The series of compounds was reacted in the catalytic cycle with benzaldehyde and gave stilbene oxides with 44% ee (sulfur analogue), 41% ee (1,3-oxathiane), and 20% ee (carbon analogue). Thus, it was concluded that the oxygen of the 1,3-oxathiane exerted a significant electronic effect in controlling the face selectivity of the ylide reactions. This electronic effect was a result of combined anomeric (higher with the sulfur analogue, not present with the carbon analogue) and Cieplak effects. A strong anomeric effect was observed in the X-ray structures of one of the 1,3-oxathianes, and an even greater one was observed in the corresponding sulfoxide (this was used as an electronic analogue of the ylide). The face selectivity of the ylide was believed to be complete in reactions with 5b. The minor enantiomer resulted from reaction of the minor conformer of the ylide, reacting again with high face selectivity. This was proven by using a more substituted diazo compound, which was expected to give much less of the minor conformer. Indeed, reaction with mesityldiazomethane gave the corresponding epoxide in essentially enantiomerically pure form.
- Aggarwal, Varinder K.,Ford, J. Gair,Fonquerna, Sílvia,Adams, Harry,Jones, Ray V.H.,Fieldhouse, Robin
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p. 8328 - 8339
(2007/10/03)
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- Cis-trans isomerization and oxidation of radical cations of stilbene derivatives
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Isomerization from cis stilbene derivatives (c-S (S = RCH=CHC6H5: 1, R = C6H5; 2, R = 4-CH3C6H4; 3, R = 4-CH3OC6H4 (= An); 4, R = 2,4-(CH3O)2C6H3; 5, R = 3,4-(CH3O)2C6H3; 6, R = 3,5-(CH3O)2C6H3; 7, AnCH=C(CH3)C6H5; 8, AnCH=CHAn)) to trans isomers (t-S) and oxidation of S with O2 were studied in γ-ray radiolyses of c-S in Ar-saturated 1,2-dichloroethane (DCE) and of S in O2-saturated DCE, respectively. On the basis of product analyses, it is suggested that a smaller barrier to c-t unimolecular isomerization for c-3.+-5.+ and 8.+ than for c-1.+, 2.+, and 6.+ due to the single bond character of the central C=C double bond for c-3.+-5.+ and 8.+ with a p-methoxyl group but not for c-l.+, 2.+, and 6.+ without a p-methoxyl group because of the contribution of a quinoid-type structure induced by charge-spin separation. The isomerization proceeds via chain reaction mechanisms involving c-t unimolecular isomerization and endergonic hole transfer or dimerization and decomposition. The isomerization of c-3.+ to t-3.+ is catalyzed by addition of 1,4-dimethoxybenzene but terminated by triethylamine. The regioselective formation of 3d in oxidation of 3.+ with O2 is explained by spin localization on the β-olefinic carbon in 3.+. The results of product analyses are compared with the rate constants of the unimolecular isomerization and the oxidation for S.+ measured with pulse radiolyses.
- Majima, Tetsuro,Tojo, Sachiko,Ishida, Akito,Takamuku, Setsuo
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p. 7793 - 7800
(2007/10/03)
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- A two-step asymmetric synthesis of pure trans-(R,R)-diaryl-epoxides
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Pure trans-(R,R)-diaryl-epoxides are obtained in two steps and under aprotic conditions using Eliel's oxathiane as the chiral auxiliary. The enantiomeric excesses, determined by chiral HPLC, are 97.9% to 99.9% and the oxathiane is recovered in 78% to 92% yield and may thus be re-used.
- Solladie-Cavallo, Arlette,Diep-Vohuule, Anh,Sunjic, Vitomir,Vinkovic, Vladimir
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p. 1783 - 1788
(2007/10/03)
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- Preparation of enantiomerically enriched (2R,3R)- or (2S,3S)-trans-2,3-diaryloxiranes via camphor-derived sulfonium ylides
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Easily available D-(+)-camphor-derived sulfides 3, 4, 6, and 7 were employed for enantioselective epoxidation via an ylide route. When benzylated or methylated sulfides were used as reagents or mediators for benzylidene transfer, stoichiometric and catalytic epoxidations were realized, respectively. Opposite asymmetric induction was achieved only when sulfides containing exo- (3 and 4) and endo- (6 and 7) alkylthio groups were used. That is, both (+)- and (-)-trans-diaryloxiranes could be obtained in excellent yields and moderate to good ee values under extremely mild conditions from the same chiral pool-derived reagents. A nonbonded interaction between the free OH in the ylides from sulfides (3, 6, and 7) and the carbonyl group of aldehydes controls the approach of the substrates to the ylidic carbon preferentially at one specified face and therefore leads to a more efficient asymmetric induction than that in the case of the ylide from methyl-protected hydroxylated sulfides 4, which cannot cause such an interaction. The same opposite asymmetric induction was also observed in the catalytic reaction with methyl-protected hydroxylated sulfide 4b and unprotected hydroxylated sulfide 3b.
- Li, An-Hu,Dai, Li-Xin,Hou, Xue-Long,Huang, Yao-Zeng,Li, Feng-Wei
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p. 489 - 493
(2007/10/02)
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- Electron-Transfer Photosensitized Oxygenation of Stilbene and Naphthalene Derivatives in the Presence of Acetate Ion. Controlling the Reaction of the Cation Radicals by Weak-Nucleophilic Salts
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The 9,10-Dicyanoanthracene (DCA)- or 9-cyanoanthracene-sensitized photooxygenation of trans-stilbene derivatives gave benzaldehyde derivatives efficiently in the presence of weak-nucleophilic salts, such as Et4NOAc and KOAc/18-crown-6 ether.The product distribution of this photooxygenation was apparently different from that of each photooxygenation in the presence of Mg(ClO4)2 and Et4NBF4 or in the absence of the salt.The DCA-sensitized photooxygenation of 2-methylnaphthalene gave phthalic acid and 4-methylphthalic acid in the presence of Nt4NOAc.These products were different from the products generated from each photooxygenation in the presence of Et4NBF4 and KClO4 or in the absence of the salt.Also, such ring-oxygenation occurred in the DCA-sensitized photooxygenation of 2,3-dimethylnaphthalene and naphthalene in the presence of Et4NOAc.These photooxygenations in the presence of Et4NOAc proceeded by the addition of an acetate ion to the cation radical of the substrate generated by a photochemical electron transfer from the substrate to the sensitizer and the subsequent reaction with O2 and the related oxygen species.
- Yamashita, Toshiaki,Tsurusako, Taiji,Nakamura, Nobuya,Yasuda, Masahide,Shima, Kensuke
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p. 857 - 862
(2007/10/02)
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- Phase transfer catalyzed reaction of some telluronium salts with aromatic aldehydes
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Under the liquid-liquid phase transfer condition, the reaction of aromatic aldehydes with benzyl dibutyl telluronium bromide were found to give epoxy compounds, while the reactions with p-chlorobenzyl dibutyl telluronium bromide were found to give epoxy compounds or olefins.
- Zhong,Shao,Liu,Lu
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p. 869 - 876
(2007/10/02)
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- Reactions of Carbonyl Compounds with Benzyltrialkylstibonium Bromide mediated by Different Strong Bases
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Reactions of carbonyl compounds with benzyltrialkylstibonium bromide mediated by alkyl-lithium gave homobenzylic alcohols, while mediated by lithium di-isopropylamide (LDA) gave a mixture of an alkene and an epoxide
- Huang, Yao-Zeng,Liao, Yi,Chen, Chen
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- GENERATION OF SULFUR YLIDES BY THE DESILYLATION OF α-TRIMETHYLSILYLBENZYL SULFONIUM SALTS
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The -sigmatropic rearrangement of sulfur ylides derived via the desilylation of several α-trimethylsilylbenzyl sulfonium salts has been studied.The initally formed ylide was found to rapidly equilibrate with the thermodynamically more stable ylide.In the absence of trapping reagents, a Sommelet-Hauser type rearrangement occurs.
- Padwa, Albert,Gasdaska, John R.
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p. 4147 - 4156
(2007/10/02)
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- DIRECT EPOXIDATION OF POLYCYCLIC AROMATIC COMPOUNDS BY SUPEROXIDE IN THE PRESENCE OF PHOSGENE DIMER
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Olefins and polycyclic aromatic compounds were oxidized to their epoxides by superoxide (O2-.) in the presence of phosgene dimer.The reaction mechanisms are discussed.
- Nagano, Tetsuo,Yokoohji, Kiyomi,Hirobe, Masaaki
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p. 3481 - 3484
(2007/10/02)
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- Ru(bpy)32+ SENSITIZED PHOTOOXIDATION REACTION OF cis-STILBENES NOVEL PRODUCTS FORMATION
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Ru(bpy)32+ sensitized photooxidation of cis-stilbenes in acetonitrile gave novel cycloadducts.Products distribution changed remarkably depending on sensitizers.
- Futamura, Shigeru,Ohta, Hiroyuki,Kamiya, Yoshio
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p. 381 - 384
(2007/10/02)
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