- Copper(i)-catalysed asymmetric allylic reductions with hydrosilanes
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A copper(i)-catalysed asymmetric allylic reduction enables a regio- and stereoselective transfer of a hydride nucleophile in an SN2′-fashion onto allylic bromides. This transformation represents a conceptually orthogonal approach to allylic substitution reactions with carbon nucleophiles. A copper(i) complex based upon a chiral N-heterocyclic carbene (NHC) ligand allows for stereoselectivity reaching 99% ee. The catalyst enables a stereoconvergent reaction irrespective of the double bond configuration of the starting materials.
- Thanh Nguyen,Thiel, Niklas O.,Teichert, Johannes F.
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p. 11686 - 11689
(2017/11/03)
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- Improvements and Applications of the Transition Metal-Free Asymmetric Allylic Alkylation using Grignard Reagents and Magnesium Alanates
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Two new N-heterocyclic carbene (NHC) ligands have been synthesized and employed in the transition metal-free asymmetric allylic alkylation (AAA) mediated by Grignard reagents and magnesium alanates. The employment of these ligands showed high yields and improved regio- and enantioselectivity in the formation of tertiary and quaternary stereocenters. Moreover, the low catalyst loading (up to 0.3 mol%) and high scalability (up to 10 mmol) of this improved methodology provide a convenient access to biologically active compounds and synthetically valuable intermediates.
- Grassi, David,Alexakis, Alexandre
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p. 3171 - 3186
(2015/11/03)
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- Short synthesis of chiral 4-substituted (S)-imidazolinium salts bearing sulfonates and their use in γ-selective reactions of allylic halides with grignard reagents
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A one-pot reaction of Boc-protected amino alcohols and 2-sulfobenzoic anhydride followed by the addition of a wide variety of primary amines has allowed rapid access to diverse libraries of amidosulfonates 1,2-C 6H4(SO3su
- Latham, Christopher M.,Blake, Alexander J.,Lewis, William,Lawrence, Matthew,Woodward, Simon
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supporting information; experimental part
p. 699 - 707
(2012/03/11)
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- γ-Selective cross-coupling of allylic silanolate salts with aromatic bromides using trialkylphosphonium tetrafluoroborate salts prepared directly from phosphine?borane adducts
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The γ-selective, palladium-catalyzed cross-coupling of sodium (Z)-2-butenyldiethylsilanolate with a variety of aromatic bromides is reported. The protocol provides high yields (73-94%) and site selectivity (γ/α, 25:1 → > 99:1) in the coupling of electron-
- Denmark, Scott E.,Werner, Nathan S.
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supporting information; experimental part
p. 4596 - 4599
(2011/10/12)
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- Enantioselective copper-catalysed allylic alkylation of cinnamyl chlorides by Grignard reagents using chiral phosphine-phosphite ligands
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The copper(I)-catalysed SN2'-type allylic substitution of E-3-aryl-allyl chlorides (cinnamyl chlorides) using Grignard reagents represents a powerful method for the synthesis of compounds carrying a benzylic stereocentre. By screening a small library of modular chiral phosphine-phosphite ligands a new copper(I)-based catalyst system was identified which allows the performance of such reactions with exceptional high degrees of regio- and enantioselectivity. Best results were obtained using TADDOLderived ligands (3 mol%), copper(I) bromide?dimethyl sulfide (CuBr?SMe2) (2.5 mol%) and methyl tert-butyl ether (MTBE) as a solvent. Various (1- alkyl-allyl)benzene derivatives were prepared with up to 99% ee (GC) in isolated yields of up to 99%. In most cases the product contained less than 3% of the linear regioisomer (except for ortho-substituted substrates). Both electron-rich and electron-deficient cinnamyl chlorides were successfully employed. The absolute configuration of the products was assigned by comparison of experimental and calculated CD spectra. The substrates were prepared from the corresponding alcohols by reaction with thionyl chloride. Initially formed mixtures of regioisomeric allylic chlorides were homogenised by treatment with CuBr?SMe2 (2.5 mol%) in the presence of triphenyl phosphine (PPh3) (3 mol%) in MTBE at low temperature to give the pure linear isomers. In reactions with methylmagnesium bromide (MeMgBr) an ortho-diphenylphosphanyl-arylphosphite ligand with an additional phenyl substituent in ortho'-position at the aryl backbone proved to be superior. In contrast, best results were obtained in the case of higher alkyl Grignard reagents (such as ethyl-, n-butyl-, isopropyl-, and 3-butenylmagnesium bromides) with a related ligand carrying an isopropyl substituent in ortho'-position. The method was tested on a multimmol scale and is suited for application in natural product synthesis.
- Loelsberg, Wibke,Ye, Shute,Schmalz, Hans-Guenther
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supporting information; experimental part
p. 2023 - 2031
(2010/10/21)
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- Cross-coupling of aromatic bromides with allylic silanolate salts
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The sodium salts of allyldimethylsilanol and 2-butenyldimethylsilanol undergo palladium-catalyzed cross-coupling with a wide variety of aryl bromides to afford allylated and crotylated arenes. The coupling of both silanolates required extensive optimization to deliver the expected products in high yields. The reaction of the allyldimethylsilanolate takes place at 85°C in 1,2-dimethoxyethane with allylpalladium chloride dimer (2.5 mol %) to afford 73-95% yields of the allylation products. Both electron-rich and sterically hindered bromides reacted smoothly, whereas electron-poor bromides cross-coupled in poor yield because of a secondary isomerization to the 1-propenyl isomer (and subsequent polymerization). The 2-butenyldimethylsilanolate (E/Z, 80:20) required additional optimization to maximize the formation of the branched (γ-substitution) product. A remarkable influence of added alkenes (dibenzylideneacetone and norbornadiene) led to good selectivities for electron-rich and electron-poor bromides in 40-83% yields. However, bromides containing coordinating groups (particularly in the ortho position) gave lower, and in one case even reversed, selectivity. Configurationally homogeneous (E)-silanolates gave slightly higher γ-selectivity than the pure (Z)-silanolates. A unified mechanistic picture involving initial γ-transmetalation followed by direct reductive elimination or σ-π isomerization can rationalize all of the observed trends.
- Denmark, Scott E.,Werner, Nathan S.
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supporting information; experimental part
p. 16382 - 16393
(2009/05/08)
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- Asymmetric cross-coupling of potassium 2-butenyltrifluoroborates with aryl and 1-alkenyl bromides catalyzed by a Pd(OAc)2/Josiphos complex
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The asymmetric cross-coupling reaction of [CH3CH= CHCH 2BF3]K with aryl or 1-alkenyl bromides selectively occurred at the γ-carbon of 2-butenylborane moiety with regioselectivities in a range of 84-99%. The enantioselectiv
- Yamamoto, Yasunori,Takada, Shingo,Miyaura, Norio
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p. 1368 - 1369
(2007/10/03)
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- γ-selective cross-coupling of potassium allyltrifluoroborates with aryl and 1-alkenyl bromides catalyzed by a Pd(OAc)2/D-t-BPF complex
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Cross-coupling reactions of [RCH=CHCH2BF3]K with aryl or 1-alkenyl bromides occurred at the γ-carbon of an allylborane moiety with perfect regioselectivities (>99%) in the presence of a palladium/D-t-BPF complex and K2COs
- Yamamoto, Yasunori,Takada, Shingo,Miyaura, Norio
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p. 704 - 705
(2007/10/03)
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- Copper catalyzed enantioselective allylic substitution by MeMgX
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Methyl Grignard undergoes highly regio (>90/10) and enantioselective (ee 91-96%) copper catalyzed allylic substitution on cinnamyl-type chlorides. CuBr (3%) and 3.3% of a chiral phosphoramidite ligand are sufficient for a complete reaction. The synthesis of a precursor of (+)-Naproxen is described. The reaction can be extended to alkyl substituted allylic chlorides (ee 72%).
- Tissot-Croset, Karine,Alexakis, Alexandre
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p. 7375 - 7378
(2007/10/03)
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