2 edition of Stereoselective alkene epoxidation using chromium salen complexes found in the catalog.
Stereoselective alkene epoxidation using chromium salen complexes
Cormac T. Dalton
|Statement||by Cormac T. Dalton.|
|Contributions||University College Dublin. Department of Chemistry.|
|The Physical Object|
|Number of Pages||253|
Stereospecific and regioselective catalytic epoxidation of alkenes by a novel ruthenium(II) complex under aerobic conditions V. Kesavan and S. Chandrasekaran, J. Chem. Soc., Perkin Trans. 1, Cited by: In this video, we have discussed about the various reagents used for the epoxidation of alkenes along with the relevant examples. The Houk Model explained using molecular models
Complexes 9 and 10 containing bulky 1,1′-dipyridil ligands are very poor and non-stereoselective catalysts which is apparently due to sterical hindrance around the reaction center. Previously, Nam et al. [ 16 ] in the oxidation catalyzed by Co(ClO 4) 2 used large excess of cis -1,2-dimethylcyclohexane (1 mmol) over MCPBA ( mmol) and Cited by: Stereoselective β-elimination of diastereomeric mixtures of 2-bromohydroxyesters is achieved by using unactivated manganese and trimethylsilyl chloride, to yield (E)-α,β-unsaturated esters with total diastereoselectivity. J. M. Concellón, H. Rodríguez-Solla, V. del Amo, Synlett, ,
1. Introduction. Nowadays, there is a growing requirement to design green synthetic protocols to reduce or to eliminate the use and generation of hazardous substances [1,2,3].Metal-Salen complexes are a wide class of organometallic compounds that have been found applications in several fields, such as catalysis [4,5], imaging , solar cells [7,8] and sensing [9,10,11,12,13].Cited by: The (salen) Co catalyst (4a) can be prepared as a mixture of cyclic oligomers in a short, chromatography-free synthesis from inexpensive, commercially available catalyst displays remarkable enhancements in reactivity and enantioselectivity relative to monomeric and other multimeric (salen) Co catalysts in a wide variety of enantioselective epoxide ring-opening by:
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In the stoichiometric asymmetric epoxidation of E-β-methylstyrene with cationic chromium−salen oxo complexes, enantioselectivity is increased by halo-substitution at the 3,3‘- and 6,6‘-positions and decreased at the 4,4‘- and 5,5‘-positions on the salen rings. Addition of triphenylphosphine oxide significantly increases selection with 3,3‘- or 5,5‘-substituents but not with 4,4 Cited by: Novel manganese complexes containing N 4 ‐tetradentate ligands derived from chiral bipyrrolidinediamines catalyze the stereoselective epoxidation of a wide array of alkenes using low catalyst loadings ( mol%) and hydrogen peroxide ( equiv.) as terminal oxidant.
This family of catalysts affords good to excellent yields (80–%) and moderate to good ees (40–73%) in short Cited by: The epoxidation of (E)-β-methylstyrene mediated by an oxochromium salen complex yields the epoxide in 92% ee in stoichiometric mode, the highest ee yet reported for a metal-mediated epoxidation of an (E)-alkene.
The effect of added donor ligands, previously substantial, has reached a ceiling with this complex. In catalytic mode a slightly reduced ee and higher yield is obtained, indicating Cited by: Catalysis of alkene oxidation by nickel salen complexes using sodium hypochlorite under phase-transfer conditions.
Journal of the American Chemical Society(12), DOI: /jaa John T. Groves, Kwang Hyun. Ahn, Robert. by: The use of metal complexes of chiral salen ligands in catalytic asymmetric synthesis has been widespread in recent years.
1 Especially useful is the manganese–salen catalyzed asymmetric epoxidation of conjugated Z-alkenes (Fig. 1, M=Mn) studied extensively by Jacobsen 2 and Katsuki. 3 We have reported4., 4.(a), 4.(b), 4.(c), 4.(d), 4.(e), 4.(f) on the complementary chiral chromium salen Cited by: The mechanism of alkene epoxidation by chromium(v) oxo salen complexes has been studied by DFT and experimental methods.
The reaction is compared to. The use of metal complexes of chiral salen ligands in catalytic asymmetric synthesis has been widespread in recent ally useful is the manganese–salen catalyzed asymmetric epoxidation of conjugated Z-alkenes (Fig.
1, M=Mn) studied extensively by Jacobsen and have reported,, on the complementary chiral chromium–salen complexes which give good Cited by: Recent Advances in Stereoselective Synthesis of 1,3-Dienes. Hu X. Peter Zhang Selective Olefination of Carbonyl Compounds via Metal-Catalyzed Carbene Transfer from Diazo Reagents.
Lei H. Li Selective Alkene Metathesis in the Total Synthesis of Complex Natural Product. Gu S.-K. Tian Olefination Reactions of Phosphorus-Stabilized Carbon.
Prior to considering the enantioselectivity obtained in the Cr(salen)-mediated AE of alkenes in terms of possible substituent-electronic effects, 2e and 3e would not have been considered good candidates for enantioselective complexes because the chromium analogue of Jacobsen's catalyst was a mediocre epoxidation catalyst and EWGs were best for Cited by: The chromium complexes of these ligands can be used in asymmetric epoxidation of alkenes.
The presence of triphenylphosphine oxide substantially raises the selectivity (ee) of the epoxidation. Chromium salen complexes with two different salicylidene moieties epoxidised E -β-methylstyrene with enantioselectivities strongly dependant on the Cited by: Chromium–salen complexes are well-known catalysts, both in heterogeneous and homogeneous systems.
Other applications of theses complexes are reported, such as, the stereoselective alkene epoxidations, and alcohol by: Asymmetric alkene epoxidation with chromium oxo salen complexes: Effect of π-rich and other types of additives Article in Molecular Catalysis (2) September with 86 Reads.
Stereoselective Synthesis of Tetrasubstituted Alkenes via Torquoselectivity-Controlled Olefination of Carbonyl Compounds with Ynolates, by Mitsuru Shindo and Kenji Matsumoto.- Stereoselective Synthesis of Z-Alkenes, by Woon-Yew Siau, Yao Zhang and Yu Zhao.- Stereoselective Synthesis of.
Advanced organic Stereoselective reactions of alkenes • Earlier, we saw that stereospeciﬁc reactions can produce single diastereoisomers • If there is a pre-existing stereogenic centre reactions can be stereoselective • In other words, the faces of the alkene are diastereotopic • Following two examples show highly diastereoselective iodolactonisations.
A (salen)manganese(III) complex bearing a chiral binaphthyl strapping unit catalyzes the enantioselective hydroxylation of indane (up to 34% ee) and the epoxidation of alkenes.
Salen ligands are a class of Schiff bases simply obtained through condensation of two molecules of a hydroxyl-substituted aryl aldehyde with an achiral or chiral diamine. The prototype salen, or N,N′-bis(salicylidene)ethylenediamine has a long history, as it was first reported inand immediately, some of its metal complexes were also by: 1.
In Mn(salen)-promoted epoxidation, the stereoselective reaction is due to a single unit of the salen. In many reactions in which Al(salen) acts as a Lewis acid, the trajectory of the incoming nucleophiles is effectively controlled by the cyclohexyldiamine backbone when hindered tert -butyl substituents are introduced in the aldehydic by: 1.
Organic Chemistry Stereoselective reactions • If there is a pre-existing stereogenic centre then reaction can be stereoselective • In such reactions two diastereoisomers could be formed but one is favoured 2 O OH Me I 2 O I Me O 82% de O Me OH I 2 O I Me O 88% de • These cyclisations are probably under thermodynamic control • This means the reactions are reversible and equilibrate.
Asymmetric epoxidation of alkenes with aqueous t-BuOOH catalyzed by novel chiral complexes of chromium(III) containing tridentate Schiff-base ligands Article in Molecular Catalysis (1) Regio- and Stereoselective Mono-Epoxidation of Dienes using Methyltrioxorhenium: Synthesis of Allylic Epoxides.
Article in The Journal of Organic Chemistry 79(21) October with Reads. Preparation of salen complex: A green solution of chromium (III) chloride hexahydrate ( g, mmol) in water ( mL) was added dropwise with vigorous stirring. The mixture was stirred for a minimum of 30 min or at least until the characteristic sky blue colour of chromium(II) chloride persisted.
The mechanism of alkene epoxidation by chromium(v) oxo salen complexes has been studied by DFT and experimental methods.
The reaction is compared to the closely related Mn-catalyzed process in an attempt to understand the dramatic difference in selectivity between the two by: Aneta Nodzewska, Agnieszka Wadolowska and Michael Watkinson, Recent advances in the catalytic oxidation of alkene and alkane substrates using immobilized manganese complexes with nitrogen containing ligands, Coordination Chemistry Reviews, Cited by: