- Radical-mediated aerobic oxidation of substituted styrenes and stilbenes
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A 2,2-azobis(isobutyronitrile)-catalyzed oxidative cleavage of alkenes with molecular oxygen as the oxidant was described. Carbonyl compounds and oxiranes were obtained in moderate yield under mild conditions. This study provided useful insights into the mechanism of aerobic oxidative cleavage of alkenes.
- Aman, Hasil,Chiu, Wei-Hua,Chuang, Gary Jing,Liu, Pin-Heng
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supporting information
p. 20103 - 20106
(2021/12/02)
-
- 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)
-
- One-pot synthesis of epoxides from benzyl alcohols and aldehydes
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A one-pot synthesis of epoxides from commercially available benzyl alcohols and aldehydes is described. The reaction proceeds through in situ generation of sulfonium salts from benzyl alcohols and their subsequent deprotonation for use in Corey–Chaykovsky epoxidation of aldehydes. The generality of the method is exemplified by the synthesis of 34 epoxides that were made from an array of electronically and sterically varied alcohols and aldehydes.
- Alfonzo, Edwin,Mendoza, Jesse W.L.,Beeler, Aaron B.
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supporting information
p. 2308 - 2312
(2018/09/14)
-
- Continuous Flow Synthesis and Purification of Aryldiazomethanes through Hydrazone Fragmentation
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Electron-rich diazo compounds, such as aryldiazomethanes, are powerful reagents for the synthesis of complex structures, but the risks associated with their toxicity and instability often limit their use. Flow chemistry techniques make these issues avoidable, as the hazardous intermediate can be used as it is produced, avoiding accumulation and handling. Unfortunately, the produced stream is often contaminated with other reagents and by-products, making it incompatible with many applications, especially in catalysis. Herein is reported a metal-free continuous flow method for the production of aryldiazomethane solutions in a non-coordinating solvent from easily prepared, bench-stable sulfonylhydrazones. All by-products are removed by an in-line aqueous wash, leaving a clean, base-free diazo stream. Three successful sensitive metal-catalyzed transformations demonstrated the value of the method.
- Lévesque, éric,Laporte, Simon T.,Charette, André B.
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p. 837 - 841
(2017/01/14)
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- The B(C6F5)3-Catalyzed Tandem Meinwald Rearrangement-Reductive Amination
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A system of three coupled catalytic cycles enabling the one-pot transformation of epoxides to amines via Meinwald rearrangement, imine condensation, and imine reduction is described. This assisted tandem catalysis is catalyzed by B(C6F5)3 resulting in the first tandem Meinwald rearrangement-reductive amination protocol. The reaction proceeds in nondried solvents and yields β-functionalized amines. In particular, β-diarylamines are obtained in high yields.
- Tiddens, Martine R.,Klein Gebbink, Robertus J. M.,Otte, Matthias
-
supporting information
p. 3714 - 3717
(2016/08/16)
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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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p. 1963 - 1968
(2016/08/10)
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- A mild access to chiral syn 1,2-diaryl glycols by stereoselective ring opening of ortho substituted trans 2,3-diaryl-oxiranes using Amberlyst 15 in H2O/THF system
-
Amberlyst 15 was an efficient and green catalyst for the reaction of 2,3-diaryloxiranes with H2O in organic co-solvent to prepare glycols in high yield. Ortho substituted trans 2,3-diaryloxiranes afforded the corresponding syn glycols stereo- and enantiospecifically. Stereoselectivity appeared related to the coordination ability of the substituents, irrespective of their electronic properties. Indeed o-OCH3 and o-OBn substituted syn glycols were obtained in high stereochemical ratios (6/1 and 10/1, respectively), and o-OTIPS and o-NO2 substituted ones were obtained as exclusive products, with the same ee of the parent epoxides.
- Lupattelli, Paolo,Chiummiento, Lucia,Funicello, Maria,Tramutola, Francesco,Marmo, Antonella,Gliubizzi, Natascia,Tofani, Daniela
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supporting information
p. 5662 - 5668
(2015/08/03)
-
- 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
-
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.
-
-
- 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
-
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.
-
-
- An effective dual copper-and sulfide-catalytic system for the epoxidation of aldehydes with phenyldiazomethane
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Epoxides have been obtained from alde-hydes and phenyldiazomethane using catalytic amounts of both the copper homoscorpionate com-plexes Tp xCuL (Tpx = homoscorpionate ligand; L = acetonitrile or tetrahydrofuran, THF) and dimethyl sulfide (SMe2) in high yields and diasteroselectivities, and with activities higher (TOF = 46 h-1) than those already known with rhodium-or copper-based cata-lysts. Among the copper(I) homoscorpionate com-plexes tested, TpBr3Cu(NCCH 3) showed the highest catalytic activity under mild conditions. The catalytic activity is controlled by electronic effects induced by the Tp x ligand as well as by the stability of the TpxCu(SR 2) adducts. Indeed, in the case of TpMs as ligand, the TpMsCu(THT) (THT = tetrahydrothio-phene) and Tp MsCu(SMe2) species could be isolated as very stable crystalline solids, the molecular struc-ture of the former being confirmed by single-crystal X-ray diffraction analysis. The in situ generation of PhCHN 2 from benzaldehyde tosylhydrazone sodium salt at 60 °C in methyl tert-butyl ether as solvent and TpMsCu(THF) as the catalyst also showed high cata-lytic activities, improving those already reported with copper-based catalysts.
- Pereira, Ana,Martín, Carmen,Maya, Celia,Belderrain, Tomás R.,Pérez, Pedro J.
-
supporting information
p. 2942 - 2951
(2014/03/21)
-
- 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)
-
- 3- and 4-uloses derived from N-acetyl- D -glucosamine: A unique pair of complementary organocatalysts for asymmetric epoxidation of alkenes
-
The 4-ulose and the 3-ulose, both derived in two steps from the α-methyl glycoside of N-acetyl-D-glucosamine (GlcNAc), act as organocatalysts in the asymmetric epoxidation of alkenes, with unprecedented complementary enantioselectivity. The best results are found with α,β-unsaturated esters as substrates, with enantiomeric ratios up to 90:10 and 11:89, respectively. Copyright
- Schoeberl, Christof,Jaeger, Volker
-
supporting information; experimental part
p. 790 - 796
(2012/05/04)
-
- Guanidine bases in synthesis: Extending the scope of the corey-chaykovsky epoxidation
-
Guanidine bases, such as 1,5,7-triazabicyclo[4.4.0]dec-1-ene (TBD) or 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-1-ene (MTBD), are highly effective reagents for the in situ generation of sulfonium ylides from sulfonium salts in Corey-Chaykovsky epoxidation reactions of aldehydes. These reactions proceed rapidly to produce the corresponding epoxides in excellent yields and with high selectivity for the trans product. Significantly, this reagent combination is applicable to both nonenolizable and enolizable aldehydes and α,β-unsaturated aldehydes.
- Phillips, David J.,Graham, Andrew E.
-
experimental part
p. 769 - 773
(2010/06/12)
-
- Copper(II) tetrafluroborate-promoted Meinwald rearrangement reactions of epoxides
-
Epoxides undergo a highly efficient Meinwald rearrangement in the presence of catalytic quantities of copper(II) tetrafluoroborate to give carbonyl compounds in high yields and with excellent selectivity. The low toxicity and ease of handling of this reagent make it an attractive alternative to the more corrosive or costly Lewis acids frequently employed.
- Robinson, Mathew W.C.,Pillinger, Kathryn S.,Mabbett, Ian,Timms, David A.,Graham, Andrew E.
-
supporting information; experimental part
p. 8377 - 8382
(2010/11/19)
-
- A new chiral organosulfur catalyst for highly stereoselective synthesis of epoxides
-
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
-
supporting information; experimental part
p. 2483 - 2487
(2009/09/08)
-
- The highly trans-selective Darzens reaction via ammonium ylides
-
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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- Regio- and stereoselective ring opening of 2,3-diaryl oxiranes by LiBr/Amberlyst 15: A new stereocontrolled access to 1,2-diaryl-2-bromo alcohols
-
(Chemical Equation Presented) Both symmetrical and non symmetrical trans-2,3-diaryloxiranes are regio- and stereoselectively opened by the LiBr/Amberlyst 15 system. In the case of symmetrical trans-stilbene oxide, the syn-versus anti-bromohydrins ratio ranged between 88/12 and 30/70, by varying the reaction temperature from 20 to -30°C. In the case of nonsymmetrical para -substituted trans-2,3-diaryloxiranes, the regioselectivity is determined by electronic effects. If one phenyl bears a strong electron-withdrawing group (as NO2 or CF3), the nucleophilic attack is totally on the β-carbon with respect to the substituted phenyl ring. With one phenyl bearing a strong electron-releasing group (OCH3), the regioselectivity is reversed. Ab initio calculation at the DFT/B3LYP/6- 31G* level, run on protonated epoxide structures, supports the formation of a cationic acyclic intermediate. Application of the method on ortho-methoxy and ortho-nitro 2,3-diaryloxiranes afforded the syn-bromohydrins in excellent yield, via regio- and stereoselective opening at either α- or β-carbon, respectively.
- Solladie-Cavallo, Arlette,Lupattelli, Paolo,Bonini, Carlo
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p. 1605 - 1611
(2007/10/03)
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- Catalytic ferrocenyl sulfides for the asymmetric transformation of aldehydes into epoxides
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Six ferrocenyl sulfides, exhibiting planar and central chiralities, have been screened as a catalytic source of asymmetric sulfonium ylides. A one-pot reaction has been achieved, involving the addition of an aldehyde, benzyl bromide, 20% molar equivalent of the ferrocenyl sulfide, sodium iodide in a mixture of tert-butanol and water. The best results were observed with enantiopure sulfide 3a, bearing a tert-butyl group. Good yields of stilbene oxides were obtained, with enantiomeric excesses ranging from 74% to 94%. trans/cis-Diastereomeric ratios ranged from 60:40 to 86:14. The chiral sulfide was recovered. An unexpected case of stereoconvergence was observed with diastereoisomers 3a and 3b. A model is proposed to account for the asymmetric induction, based on a conformation locked by the tert-butyl group and the interplay of planar and remote central chiralities.
- Miniere, Stephanie,Reboul, Vincent,Metzner, Patrick,Fochi, Mariafrancesca,Bonini, Bianca Flavia
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p. 3275 - 3280
(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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- 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
-
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)
-
- Experimental evidence for multiple oxidation pathways in the (salen)Mn-catalyzed epoxidation of alkenes
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The substrate electronic effects on the selectivity in the catalytic epoxidation of para-substituted cis stilbenes 2a-i were investigated by using (R,R)-[N,N′-bis(3,5-di-tBu-salicylidene)-1,2-cyclohexanediamine] manganese(III) chloride 1 in benzene as the catalyst with iodosobenzene as the terminal oxidant. A Hammett study of the selectivity results reveals a stronger electrophilic character than previously assumed in the (salen)Mn-catalyzed reaction. In general, the best correlations with the experimental values were obtained by using the Hammett σ+ values, which gave ρ = -1.37 for the rate of cisepoxide formation and ρ = -0.43 for the rate of the stepwise process leading to the corresponding trans product. The reaction involves two separate pathways as indicated also by the competitive breakdown of the intermediate on the path to trans epoxide for methoxy-substituted substrates. The asynchronicity in the concerted pathway leading to cis epoxide is apparent for 4-methoxy-4′-nitrostilbene, which yields cis epoxide with 75% ee entirely as a result of electronic effects.
- Linde, Christian,Koliai, Nordine,Norrby, Per-Ola,Akermark, Bjoern
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p. 2568 - 2573
(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)
-
- Iron lewis acid catalyzed reactions of phenyldiazomethane with aromatic aldehydes
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The iron Lewis acid 1 was found to catalyze reactions of phenyldiazomethane and aromatic aldehydes to give cis-epoxides along with the corresponding ketones. The yield of the epoxide increased with electron- withdrawing substituents on the aldehyde, while little or no epoxide was formed with electron-donating substituents. The reaction was found to go through the coordination of the aldehyde to the iron Lewis acid instead of a carbene intermediate.
- Mahmood, Syed J.,Saha, Anjan K.,Mahmun Hossain
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p. 349 - 358
(2007/10/03)
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- Process for the preparation of an oxirane, azirdine or cyclopropane
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A process for the preparation of an oxirane, aziridine or cyclopropane of formula (I) wherein, X is oxygen, NR4 or CHR5 ; R1 is hydrogen, alkyl, aryl, heteroaromatic, heterocyclic or cycloalkyl; R2 is hydrogen, alkyl, aryl, heteroaromatic, CO2 R8, CHR14 NHR13, heterocyclic or cycloalkyl; or R1 and R2 join together to form a cycloalkyl ring; R3 is hydrogen, alkyl, aryl, heteroaromatic, CO2 R8, R83 Sn, CONR8 R9 or trimethylsilyl; R4 and R5 are, independently, alkyl, cycloalkyl, aryl, heteroaromatic, SO2 R8, SO3 R8, COR8, CO2 R8, CONR8 R9 or CN, or R4 can also be P(O)(aryl)2 ; R8 and R9 are independently alkyl, aryl or arylalkyl; R13 and R14 are independently hydrogen, alkyl or aryl; the process comprising reacting a mixture of a compound of formula (II), wherein R1, R2 and X are as defined above, and a sulphide of formula SR6 R7, wherein R6 and R7 are independently alkyl, aryl or heteroaomatic, or R6 and R7 join together to form a cycloalkyl ring which optionally includes an additional heteroatom, with either (i) a metallocarbon obtainable by reacting an alkylmetal with a methane derivative of formula CHR3 X'X", wherein R3 is as defined above, and X' and X" are independently, a leaving group, or (ii) a metallocarbon obtainable by reacting a compound of formula (III), (wherein R3 may not be hydrogen) with a suitable organometallic or inorganic reagent.
- -
-
-
- A Novel Catalytic Cycle for the Synthesis of Epoxides Using Sulfur Ylides
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A novel, neutral catalytic cycle for the synthesis of epoxides from carbonyl compounds and diazo compounds using catalytic quantities of transition metal salts and sulfides has been developed.In this catalytic cycle, the diazo compounds is decomposed by the transition metal salt to give a metallocarbene, and this is picked up to the sulfide to give a sulfur ylide, which then reacts with the aldehyde to give an epoxide and returns the sulfide back into the catalytic cycle.To obtain good yields of epoxides it is necessary to maintain a low concentration of the diazo compound (by slow addition), otherwise dimerisation of the diazo compound is the dominant reaction.Factors affecting the outcome of the reaction were studied.The reactions are relatively insensitive to solvent, but are sensitive to the structure of the sulfide, the metal salt and the concentration.Unhindered sulfides give good yields of epoxides with any metal salt, but with hindered sufides higher yields are obtained with Cu(acac)2 than with Rh2(OAc)4.The yields of epoxides are sensitive to sulfide concentration especially when using substoichiometric amounts of sulfides.Higher concentration leads to faster rates of formation and subsequent reaction of the sulfur ylides, and consequently to higher yields.This novel catalytic cycle has also been applied to base-sensitive aldehydes.We found that our new catalytic cycle for epoxidation gives much improved yields of epoxides compared to those obtained by traditional sulfur ylide chemistry and is tolerant to a wide variety of sensitive functional groups.Ketones also participate in the catalytic cycle, although they give reduced yields of epoxides compared to aldehydes and require a slightly elevated temperature. - Keywords: catalysis; diazo compounds; epoxidations; sulfur ylides; synthetic methods
- Aggarwal, Varinder K.,Abdel-Rahman, Hesham,Fan, Li,Jones, Ray V. H.,Standen, Mike C. H.
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p. 1024 - 1030
(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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- A NOVEL CATALYTIC CYCLE FOR THE SYNTHESIS OF EPOXIDES USING SULFUR YLIDES, AND APPLICATION TO THE SYNTHESIS OF CYCLOPROPANES AND AZIRIDINES.
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We have developed a new catalytic cycle for the synthesis of epoxides from carbonyl compounds and diazocompounds.These reactions are mediated by catalytic quantities of rhodium acetate (0.01 eq.) and dimethyl sulfide (0.2 eq.).In this catalytic cycle, phenyl diazomethane is decomposed by rhodium acetate to give a metallocarbene and this reacts with the sulfide to give a sulfur ylide which in turn reacts with the aldehyde to give an epoxide and returns the sulfide back into the catalytic cycle.The use of catalytic amounts of chiral sulfides gives non-racemic epoxides.It has been found that other diazocompounds can be used in the catalytic cycle e.g.N,N-diethyl diazoacetamide.In addition, it has been found that substitution of aldehydes for enones furnishes cyclopropanes, and substitution with imines gives aziridines.For the preparation of terminal epoxides, diazomethane could not be used instead of phenyl diazomethane.Instead, it was discovered that terminal epoxides could be prepared using diethyl zinc, chloroiodomethane, dimethyl sulfide and an aldehyde.A second catalytic cycle for epoxidation has therefore been developed.Key Words catalytic, asymmetric synthesis, sulfur ylide, epoxide, aziridine, cyclopropane, rhodium acetate, Simmons Smith.
- Aggarwal, Varinder K.,Abdel-Rahman, Hesham,Thompson, Alison,Mattison, Beverley,Jones, Ray V. H.
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p. 283 - 292
(2007/10/02)
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- Chiral sulfur-reagents for the preparation of optically active epoxides
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Acyclic chiral sulfides which could be easily synthesized in both enantiomeric forms leading to poor yields and/or to racemic epoxides, Eliel's oxathiane reagent was used and proved to provide chiral trans diarylepoxides in high yield (70-80%) and enantiomeric purities up to 70-100%, with no rearrangement problems. It was also found that phase-transfer conditions were the easiest and the most efficient for these reactions.
- Solladie-Cavallo,Adib
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p. 2453 - 2464
(2007/10/02)
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- Reaction of Diazonium Salts with Transition Metals. Part 11. Palladium-catalyzed Aryldesilylation of Alkenylsilanes by Arenediazonium Salts
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Under palladium(0) catalysis, both (E)- and (Z)-RCH=CHSiMe3(R=Rh, 4-MeC6H4, 4-NO2C6H4, n-C6H13, and MeOCH2) were easily aryldesilylated by ArN2X(Ar=Ph, 4-MeC6H4, 4-BrC6H4 and 4-NO2C6H4; X=BF4, PF6, and Cl) to give (E)-RCH=CHAr and RC(Ar)=CH2 as the main products at 25 deg C in acetonitrile. anti- and syn-1,2-Elimination of Pd(0) and Me3Si from the adducts, threo- and erythro-RCH(PdX)CHSiMe3, generated from ArPdX and (E) and (Z)-RCH=CHSiMe3, respectively, are proposed for the formation of (E)-RCH=CHAr from either isomer of RCH=CHSiMe3.
- Ikenaga, Kazutoshi,Kikukawa, Kiyoshi,Matsuda, Tsutomu
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p. 1959 - 1964
(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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- Flash Vacuum Thermolysis of 1,3-Dioxolan-4-ones
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Flash vacuum thermolysis of 1,3-dioxolane-4-ones yields aldehydes and ketones as the major products as the result of apparent decarboxylation of α lactones formed by collapse of a 1,3 dipole.When phenyl substituents are present, epoxides are also formed via the intermediacy of a carbonyl ylide.
- Cameron, Tim B.,El-Kabbani, Fiesal M.,Pinnick, Harold W.
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p. 5414 - 5417
(2007/10/02)
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- Studies on Unstabilized ?-Sulfuranes: Synthesis of trans-1,2-Disubstituted Epoxides
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4-Nitrobenzylidenedimethylsulfurane, a semi-stabilized sulfonium ylide has been generated by the attack of methylsulfinyl carbanion in dimethylsulfoxide and reacted with a series of substituted benzaldehydes, furfural and benzylideneacetophenone to afford trans-1,2-disubstituted epoxides in fair to good yields.The structural assignments of the products are based on IR and NMR spectral evidences. - Keywords: 4-Nitrobenzylidenedimethylsulfurane
- Tewari, R. S.,Awasthi, A. K.,Chaturvedi, S. C.
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p. 1565 - 1568
(2007/10/02)
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