Reaction of (trimethylstannyl) copper reagents with α, β-acetylenic esters

The stereochemical course of the conjugate addition of various (trimethylstannyl)cuprate (or copper) reagents to α, β-acetylenic esters is dependent on the constitution of the reagent and on the structure of the substrate.     

A novel method for the terpene synthesis by the ring-opening reaction of β-methyl-β-propiolactone

A new route for the terpene synthesis is investigated, which undergoes via terpene carboxylic acids as key intermediates obtained by the regiospecific ring opening of β-methyl-β-propiolactone with a cuprate or with a Grignard reagent in the presence of a copper catalyst.     

Stereoselective syntheses of piperidinones and their modification by organometallic coupling reactions

Dehydropiperidinones stereoselectively obtained from N-arabinosyl imines were iodinated at the enaminone structure. Knochel iodine-magnesium exchange afforded Grignard compounds of these piperidinone derivatives which reacted, either directly or after transmetalation to zinc or copper intermediates, with alkyl-, aryl- or acylhalides to give correspondingly substituted piperidinones. Stereoselective conjugate allyl cuprate addition to a thus obtained 5-allyl dehydropiperidinone and ring-closing metathesis of the product gave a hydroquinolinone containing three stereogenic centers.     

The Mechanism of 1,4- and 1,6-Cuprate Additions: The First Determination of Activation Parameters

With a direct kinetic study , activation parameters for the 1,4-cuprate addition to enones (see the Arrhenius plot,▴) and the 1,6-addition to acceptor-substituted enynes (█) were determined for the first time. Both reactions might involve σ copper(III ) species which are formed by oxidative addition of the respective substrate to the cuprate.     

Organocuprate conjugate addition: structural features of diastereomeric and supramolecular pi-intermediates

In the reaction pathway of conjugate additions with organocuprate reagents, Cu(I) pi-complexes and Cu(III) sigma-complexes have been identified as central, NMR-detectable intermediate species. However, no experimental evidence for the structures of pi-intermediates with extensive chiral enones or the principal aggregation level and aggregate structure of pi-complexes in diethyl ether has been available so far. Furthermore, the structural characteristics of pi-complexes which are essential for their high reactivities and diastereoselectivities have not yet been rationalized experimentally. Therefore, the pi-intermediates of 4,4a,5,6,7,8-hexahydro-4a-methyl-naphthalen-2(3H)-one and Me2CuLi or Me2CuLi x LiX (X = I, CN) in diethyl ether are investigated in detail. For the first time, the formation of two intermediate cuprate enone pi-complexes on both sides of the double bond is observed. In addition, the conformation of the enone adopted in the major beta-face pi-complex rationalizes the exclusive syn addition observed in the synthetic product. For the investigation of the aggregation level and structure, a NMR screening of pi-complexes with Me2CuLi x LiX (X = I, CN) and three achiral enones is performed, which simplifies the spectra by the generation of enantiotopic pi-complexes. Thus, NMR diffusion experiments on cuprate intermediates and the detection of scalar couplings across copper without isotope labeling are possible for the first time. Extensive NMR studies, including those of cyclohexanone complexes, show that, in principle, salt-free dimethylcuprate is able to complex the carbonyl group. However, in the presence of salt, the carbonyl-complexing aggregates are composed of salt and cuprate moieties. These mixed aggregates cause the formation of large supramolecular pi-intermediate structures which control their reactivity. The pi-complexing cuprate units show a bent geometry as a general structural feature that is unaffected by the presence or kind of salt and the type of enone. Thus, the high diastereoselectivity and the reactivity of organocuprate 1,4-addition reactions are for the first time rationalized on the basis of structural characteristics of selected pi-intermediates.     

Copper(I)‐Catalyzed Interrupted Click/Sulfenylation Cascade: One‐Pot Synthesis of Sulfur Cycle Fused 1,2,3‐Triazoles

Herein, we report a practical protocol for the synthesis of sulfur cycle fused 1,2,3‐triazoles through a copper(I)‐catalyzed tandem click/intramolecular sulfenylation reaction. The reaction proceeded via a copper‐catalyzed alkyne azide cycloaddition, followed by interception of the in situ formed cuprate‐triazole intermediate with p‐toluenesulfonothioate. This reaction shows broad substrate scope, complete regioselectivity, and excellent functional group tolerance under mild reaction conditions.     

Regio- and enantioselective control in the reactions of alpha-(N-carbamoyl)alkylcuprates with allylic phosphates

Alpha-(N-carbamoyl)alkylcuprates (RCuCNLi or R2CuLi) react with allylic phosphates to afford homoallylic amines in good chemical yields. Regioselectivity is governed by steric factors in both the cuprate reagent and phosphate substrate and systems can be designed to give either the S(N)2' or S(N)2 substitution product cleanly. Excellent enantioselectivities can be achieved with either a scalemic alpha-di[(N-carbamoyl)alkyl]cuprate and an achiral phosphate or with a scalemic allylic phosphate and an achiral cuprate reagent. [reaction: see text]     

The regiochemistry of the stannylcupration of allenes: synthesis of allylstannanes using the lower order cuprate (Bu3Sn)CuCNLi

The lower order cuprate (Bu₃Sn)CuCNLi, prepared by mixing 1 equiv of tributylstannyllithium and 1 equiv of copper(I) cyanide, reacts with allenes showing a regiochemistry opposite to that previously reported for higher order stannylcuprates. Capture of the intermediate allylstannane-vinylcuprate species with different electrophiles allows the selective formation of allylstannanes with different substitution pattern. Reaction with acetylenes was also checked.     

Electron density distribution in potassium bis -(carbonato)cuprate(II)

The electron density distribution in potassiumbis-(carbonato)cuprate(II) has been analyzed using x-ray diffraction data from an earlier structure determination. While the copper-ligand geometry is close to square planar the deformation density near the metal is strongly asymmetric. There are local maxima near the copper atom along the line of the Cu-K vectors. These resemble features found in corresponding regions in normal length metal-metal bonds. The observation is consistent with the long range nature of the Coulomb potential associated with the potassium ion.     

Copper(I)‐Catalyzed Regioselective Addition of Nucleophilic Silicon Across Terminal and Internal Carbon–Carbon Triple Bonds

The copper(I) alkoxide‐catalyzed release of a silicon‐based cuprate reagent from a silicon–boron pronucleophile is applied to the addition across carbon–carbon triple bonds. Commercially available CuBr?Me₂S was found to be a general precatalyst that secures high regiocontrol for both aryl‐ and alkyl‐substituted terminal as well as internal alkynes. The solvent greatly influences the regioisomeric ratio, favoring the linear regioisomer with terminal acceptors. This facile protocol even allows for the transformation of internal acceptors with remarkable levels of regio‐ and diastereocontrol.     

Reactivity of RCu,BF3 and R2 CuLi,BF3 towards allylic acetals and ethers

Organocopper and cuprate reagents associated with Lewis acids, are highly reactive towards allylic acetals and ethers. Displacements of the alkoxy group occurs by SN₂' attack according to the various parameters of the reaction.     

Asymmetric Catalysis with Silicon‐Based Cuprates: Enantio‐ and Regioselective Allylic Substitution of Linear Precursors

An enantio‐ and regioselective allylic silylation of linear allylic phosphates that makes use of catalytically generated cuprate‐type silicon nucleophiles is reported. The method relies on soft bis(triorganosilyl) zincs as silicon pronucleophiles that are prepared in situ from the corresponding hard lithium reagents by transmetalation with ZnCl₂. With a preformed chiral N‐heterocyclic carbene–copper(I) complex as catalyst, exceedingly high enantiomeric excesses are achieved. The new method is superior to existing ones using a silicon–boron reagent as the source of the silicon nucleophile.     

Kinetics and mechanism of oxidation of S2O 32? by potassium bis (tellurato) cuprate(III)

The kinetics of oxidation of sodium thiosulphate by potassiumbis(tellurato) cuprate(III) in an alkaline medium has been reported. The reaction is first order in [S₂O ₃ ²⁻ ] but zero order in copper(III). Hydroxide ions are found to retard the oxidation rate. A rate expression rationalising the kinetic data has been derived. Sodium tetrathionate has been found to be the product of oxidation.     

Carbocupration-functionalization of arynes: rapid access to variably ortho-substituted ((E)-3-phenylprop-1-enyl)silanes

A consecutive three-component coupling reaction involving a lithium di[3-(prop-1-enyltrimethylsilyl)]cuprate, variably substituted ortho-arynes, and a selection of common electrophiles is described. The method affords readily functionalized homobenzylic vinylsilanes with exceptional E-diastereoselectivity and allows for in situ incorporation of carbon- or heteroatom-based electrophiles into the arene.     

Diastereodivergent behavior of alkyl versus cyano allenylcuprates toward aldehydes: a key role for lithium

The stereodivergent behavior of allenyl(cyano)- and allenyl(alkyl)cuprates toward aldehydes, providing a selective preparation of both syn- and anti-homopropargylic alcohols, is described. This study, which combines both experimental and theoretical support, shows that the copper nontransferred "dummy ligand" controls the localization of the lithium cation with respect to the allenylcuprate moiety. As a consequence, Li(+) acts as a Lewis acid activator but also controls the diastereoselectivity during the addition of allenylcuprates onto aldehydes. The combined high selectivity, efficiency, and versatility of these cuprate compounds opens the way to new one-pot synthetic procedures, as illustrated by the combined Klein rearrangement/transmetalation methodology described herein.     

Halogen- and N-haloimide-promoted homo- and heterocoupling of alpha-(N-carbamoyl)alkylcuprates and alpha-(alkoxy)alkylcuprates

Both homo- and mixed lithium di-alpha-(heteroatom)alkylcuprates readily dimerize upon addition of halogens (e.g., I(2), Br(2)) or N-halosuccinimides to afford the coupled products in excellent yields. Higher yields result when the requisite alpha-(heteroatom)alkyllithium reagents are generated via deprotonation rather than by transmetalation of the corresponding stannanes. Mixed lithium dialkyl- or alkyl(aryl)cuprate reagents containing one alpha-(heteroatom)alkyl ligand and one simple alkyl or aryl ligand give significantly lower yields of coupled product. Low enantioselectivity has been achieved in the oxidative coupling of lithium (n-Bu)(2-pyrrolidinyl)cuprate.     

Polyol—Metall-Komplexe. III. Lithium-bis(oxolandiolato)cuprat-Tetrahydrat und Lithium-μ-propantriolato-cuprat-Hexahydrat — zwei homoleptische Kupfer(II)-Komplexe mit Polyolat-Liganden aus den mehrfach deprotonierten Polyolen Anhydro-erythrit und Glycerol

Polyol Metal Complexes. III. Lithium Bis(oxolanediolato)cuprate Tetrahydrate and Lithium μ-Propanetriolatocuprate Hexahydrate — Two Homoleptic Copper(II) Complexes with Polyolate Ligands Derived from the Multiply Deprotonated Polyols Anhydro-erythritol and Glycerol . In the blue-violet crystals of lithium bis{meso-oxolane-3, 4-diolato(2 - )}cuprate tetrahydrate, Li₂[Cu(C₄H₆O₃)₂] · 4H₂O ( 1 ) (P2₁/c, a = 706.2(4), b = 1114.0(6), c = 958.3(5) pm, β = 107.67(3)°, Z = 2, R_w = 0.022), square-planar coordinated copper(II) ions are bound to twofold deprotonated anhydro-erythrol ligands (Cu? O 194.36(17) and 191.83(17) pm). The oxygen ligator atoms of the mononuclear cuprate ions are bound to lithium ions or they are acceptors in asymmetrical hydrogen bonds. Trinuclear tris-{μ-propanetriolato(3 - )}tricuprate ions with triply deprotonated glycerol as ligands are present in the deep blue columns of LiCuC₃H₅O₃ · 6H₂O ( 2 ) (P3 c1, a = 1 278.8(6), c = 2 420.5(12) pm, Z = 12, R_w = 0.059), which has been prepared for the first time by Bullnheimer [2]. The copper(II) ions in 2 are also bound to alkoxide oxygen atoms in square-planar coordination (Cu? O 190.7(7) and 192.4(8), Cu? μ-O 196.6(6) and 195.0(7) pm). The hydrogen bond system and the content of channels parallel [001] are described in terms of a disorder model.     

高序铜试剂在α-亚烷基-γ-丁内酯合成中的应用

本文报道了通过以高序铜代替低序铜对炔酸酯加成得到的取代(α-乙酯基乙烯基)铜与端基或环状环氧化合物的立体选择性反应，较高产率的合成α,β-取代烯酯，进而可合成α-亚烷基-γ-丁内酯类衍生物。     

Bis(1,4-di-tert-butyl-1,4-diazabutadiene)copper(i) [(3,6-di-tert-butyl-o-benzosemiquinono)(3,6-di-tert-butyl-catecholato)cuprate(ii)]. The molecular structure and intramolecular electron transfer

Bis(1,4-di-tert-butyl-1,4-diazabutadiene)copper(i) [(3,6-di-tert-butyl-o-benzosemiquinono)(3,6-di-tert-butylcatecholato)cuprate(ii)] (1) was synthesized. Complex 1 contains the 1,4-di-tert-butyl-1,4-diazabutadiene and 3,6-di-tert-butyl-o-benzoquinone ligands in the reduced form. The structure of 1 was established by X-ray diffraction analysis. The ESR spectra indicate that dissolution of complex 1 in organic solvents (toluene, THF, CH₂Cl₂, etc.) leads to its symmetrization to give neutral complex 2, which occurs in solutions as an equilibrium mixture of two redox isomers, viz., catecholate (Cat) complex 2c and semiquinone (SQ) complex 2s. In the coordination sphere of the copper atom, the reversible intramolecular metal—ligand electron transfer can proceed as successive steps as exemplified by the reactions of 2 with CO and 2,6-dimethylphenylisonitrile. Copper(i) o-semiquinone complex 2s can be reversibly transformed into copper(ii) catecholate complex 2c through electron transfer from the copper(i) atom to the SQ ligand. The subsequent addition of the neutral ligand (CO or CNAr) to 2c induces, in turn, electron transfer from the Cat ligand to the copper(ii) atom accompanied by the transformation of the catecholate complex into the o-semiquinone complex. In the case of CO, this transformation is also reversible and is efficiently controlled by the temperature.