Copper Reagents Research Articles

Variable coordination modes for 1,1′-bis(diphenylphosphino)ferrocene (dppf) mono- and di-chalcogenides or -oxides (dppfE and dppfE 2; E = O, S or Se) in copper(I) complexes. Crystal structure of [{Cu(dppf)} 2(μ-dppfS 2)] (BF 4) 2 and [Cu(dppfSe) 2]BF 4

Reaction of [Cu(MeCN) 4]BF 4 with the phosphine Fe[ η 5-C 5H 4PPh 2] 2 (dppf) and its disulfide (dppfS 2) sequentially in chlorinated solvents led to the dinuclear tricoordinate complex [{Cu(dppf- P, P′)} 2( μ-dppfS 2- S, S′)] (BF 4) 2 ( 1), whereas reaction of the copper reagent with dppf and its diselenide (dppfSe 2) gave the bis-chelate dppf-monoselenide compound [Cu(dppfSe- P, Se) 2]BF 4 ( 2). Similarly, the E = O or S relevant complexes [Cu(dppE- P, E) 2]BF 4 were obtained by reaction of the copper(I) precursor with the dppf-monoderivatives [ η 5-C 5H 4PPh 2]Fe[ η 5-C 5H 4P(E)Ph 2] (dppfE). The complexes have been characterized by 1H and 31P NMR spectroscopy. Single-crystal X-ray structure determinations were performed for complexes 1 and 2. Complex 1 crystallizes as CHCl 3 ( 1a) or CHBr 3 ( 1b) monosolvates. The cation of 1 is exactly centrosymmetric and shows a distorted trigonal planar coordination at copper with a PCuP angle of 115.7(1)° and the SCuP angles of 138.6(1) and 104.3(6)°, as mean values from 1a and 1b. In complex 2 the coordination geometry around the metal atom is markedly distorted tetrahedral with the two dppfSe moieties acting as chelating ligands with bite angles of 111.5(2) and 116.8(2)°. The Se(1)CuSe(2) angle (103.4(2)°) approaches the value for tetrahedral geometry, while the remaining angles differ significantly from the ideal value ranging from 96.1(2) to 121.9(3)°. The CuSeP angles (124.5(2) and 132.9(2)°) point towards a substantially sp 2 hybridization of the selenium atom.

Preparation of α-Arylseleno-substituted Zinc and Copper Organometallics and their Application in the Synthesis of α-Arylselenomethyl Ketones

α-Arylseleno-substituted zinc and copper organometallics, prepared by zinc insertion into the carbon–chlorine bond of α-chloromethyl aryl selenides and with CuCN–2LiCl transmetallation to the corresponding copper reagents, react with acyl chlorides to give α-arylselenomethyl ketones based on the formation of a new carbon–carbon bond.

Synthesis of α-amino acids using amino acid γ-anion equivalents: synthesis of 5-oxo α-amino acids, homophenylalanine derivatives and pentenylglycines

Treatment of protected iodohomoalanine 7 with Rieke copper leads to the formation of an organocopper reagent 10 which reacts with electrophiles in moderate yield to give enantiomerically pure α-amino acid derivatives 11, 12 and 13. Alternatively, reaction of the fully protected iodohomoalanine derivative 15 with activated zinc gives the corresponding alkylzinc iodide 14, which reacts under palladium catalysis with a range of electrophiles (aryl iodides and acid chlorides) to give the corresponding adducts 19 and 22. While the reactions with aryl iodides provide acceptable yields in THF as solvent, the corresponding reactions with acid chlorides requires dimethoxyethane or, preferably, a combination of toluene and dimethylacetamide under ultrasonication, for good results. The alkylzinc iodide 14 can be transformed into a zinc–copper reagent 16 which reacts with allylic halides, and with reactive acid chlorides, to give the corresponding adducts 22l, 24–26 in reasonable yields.

ChemInform Abstract: Highly Regio‐ and Stereo‐Selective Alkyl Substitution with Copper Reagents for the Construction of Chiral Trifluoromethylated Quaternary Carbon Centres.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A New Route for the Preparation of Substituted 2,2-Difluorostyrenes and a Convenient Route to Substituted (2,2,2-Trifluoroethyl)benzenes

The (2,2-difluoroethenyl)zinc reagent II is coupled with aryl iodides or bromides in the presence of Pd(PPh3)4 in DMF to give the corresponding 2,2-difluorostyrenes IV. The 4-substituted (tetrafluoroaryl)copper reagents are coupled with 2,2-difluoro-1-iodoethylene (I) to produce the corresponding styrene derivatives VII. Both methods provide good yields of the coupled products. These products react with wet KF in DMF or DMSO to form the (2,2,2-trifluoroethyl)benzene derivatives VIII in good yields.

A New Synthetic Approach to Forskolin: Construction of the ABC Ring System from d-Galactose

Intramolecular Diels−Alder reaction of dienyne 14 afforded naphthopyran 18 which underwent 1,4-addition of methyl copper reagent to give the functionalized tricyclic system of forskolin 17. The synthesis of dienyne 14 is based on a stereoselective introduction of carbon side chains at C(1) and C(2) of tri-O-acetyl-d-galactal via C-Ferrier followed by Claisen−Ireland rearrangements.

The Schiff bases of salicylaldehyde and aminopyridines as highly sensitive analytical reagents

The analytical applicability of heteroaromatic Schiff bases, 2-(3-pyridylmethyliminomethyl)phenol (compound 1), 2-(2-pyridyliminomethyl)phenol (compound 2), 2-(2-amino-3-pyridyliminomethyl)phenol (compound 3), N, N′-bis(salicylidene)-2,3-pyridinediamine (compound 4), N, N′-bis(salicylidene)-2,6-pyridinediamine (compound 5) and 2-(2-amino-4-methox-ymethyl-6-methyl-3-pyridylmethyliminomethyl)phenol (compound 6), was proved. The investigation included a study of the characteristics that are essential for solvent extraction and for the spectrophotometric and spectrofluorimetric determinations of copper. Despite structural similarities, the investigated Schiff bases exhibited different behaviour in solution. Compounds 2–5 adopted predominantly the enolimino form in most solvents, whereas compound 1 was partially present as ketoamine in the solutions of polar solvents. Compound 6 was found to be the tautomeric mixture of cyclic diamine and enolimine in most solvents. All the investigated Schiff bases were capable of quantitatively extracting transition metals into chloroform. In the case of Cu(II), compound 4 proved to be an effective extractant in the range 5 < pH < 12, compounds 1 and 6 were effective in the range 6 < pH < 12, whereas compounds 2, 3 and 5 were effective only in the alkaline medium above pH 9. The spectrophotometric determination of Cu(II) after extraction was very sensitive and selective with regard to Cd(II) and Pb(II). Highest sensitivity was achieved with compound 4 ( ϵ 430 = 2.1 × 10 4 mol −1 1 cm −1). This characteristic was favourable compared to other well-known copper reagents. Since the fluorescence of Schiff bases was quenched by Cu(II), Mn(II), Fe(III), Ni(II) and Cr(III), the sensitivity as well as the selectivity were further enhanced using the spectrofluorimetric procedure. Additional advantages of these compounds to other reagents for copper(II) are simple preparation and a detailed knowledge of their equilibria.

ChemInform Abstract: Tetramethylethylene Diamine/Trimethylsilyl Chloride Mediated Addition of Benzyl Copper Reagents to α,β‐Unsaturated Esters.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: A Short and Selective Synthesis of (S)‐Geranylcitronellol via Conjugate Addition of a Functionalized Copper Reagent to 2‐Substituted exo‐Bornyl Crotonates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Highly regio- and stereo-selective alkyl substitution with copper reagents for the construction of chiral trifluoromethylated quaternary carbon centres

A new route for the asymmetric construction of quaternary carbon centres containing a trifluoromethyl group has been established using a highly regio- and stereo-selective S N 2′ reaction of organocopper and organocuprate reagents with allylic mesylates 4 and 8.

Reaction of 2-(Alkylthiomethyl)phenyllithium with Copper(I) Halides and Structure and Properties of One of the Products—Copper(I) Complexes of 2,2′-Bis(alkylthiomethyl)biphenyl

Abstract The title reactions did not afford the corresponding organocopper compound as a stable entity, but rather a dimerized biphenyl compound (2,2′-bis(alkylthiomethyl)biphenyl), its copper(I) halide complex, and alkyl benzyl sulfide. Their yields were influenced by the kind of halides in the copper reagent. The stability and reactivity of the intermediate organocopper compound is discussed on the basis of the ligand-metal interactions. The copper(I) halide complex with the biphenyl which carries two sulfane ligands has a unique polymeric structure in crystals, as evidenced by X-ray analysis, whereas it dissociates into a monomeric form on dissolution in organic solvents. The properties of the complexes were examined by NMR and XPS as well.

Tetramethylethylene diamine/trimethylsilyl chloride mediated addition of benzyl copper reagents to α,β-unsaturated esters

Several benzylic copper reagents, benzylcopper, 4-methoxybenzylcopper and 1-phenylethylcopper, facilitate the conjugate addition of the corresponding benzyl ligands to α,β-enoates in the presence of tetramethylethylene diamine and trimethylsilyl chloride in high yields.

A short and selective synthesis of ( S)-geranylcitronellol via conjugate addition of a functionalized copper reagent to 2-substituted exo-bornyl crotonates

An asymmetric synthesis of the diterpene ( S)-geranylcitronellol 1a and its acetate 1b is reported. The chirality is induced by TMSI-promoted conjugate addition of a homoallylic monoorganocopper reagent to 2-naphthyl- exo-bornylcrotonate, which proceeds with more than 98% diastereomeric excess.

Coupling Reaction of Alkynyliodonium Salts with Alkynylcopper Reagents. A New Access to Liquid-Crystalline 1,3-Butadiynes

Abstract 1,4-Disubstituted 1,3-butadiynes bearing long alkyl and alkoxy chains are seletively prepared by the coupling reaction of alkynyliodonium salts with alkylcopper reagents. The length of the alkyl chains both in the alkynyliodonium salts and in the copper reagents is not the significant factor of the coupling reaction and the coupling reaction affords unsymmetrical 1,4-disubstituted 1,3-butadiynes bearing long alkyl chains in good yields. The 1,3-butadiynes prepared in the present study exhibit mesogenic properties.

Synthèse d'analogues structuraux de thaxtomines, phytotoxines responsables de la gale de la pomme de terre

Cross coupling reactions of lithiated 2,5-piperazinedione anions with gramine methosulfate and alkylhalides were shown to be catalyzed by copper reagents, e.g. dilithium tetrachlorocuprate and copper (I) iodide. Based on this findings, the results of the first method for preparation of racemic thaxtomins are reported. Compound 1c, chosen as a synthetic model, was prepared in five steps in 19% overall yield. The key step was reaction of the lithiated anion of sarcosine anhydride with gramine methosulfate in the presence of a catalytic amount of dilithium tetrachlorocuprate in THF. The remainder of the sequence involved protection of the indole NH, aldol condensation with 3-benzyloxybenzaldehyde, bromohydrin formation and catalytic hydrogenation.

New cytochalasins: Synthetic studies of a novel HIV-1 protease inhibitor

By using a benzyl copper reagent (e.g. 10→11) in combination with titanium enolate chemistry (e.g. 12→13) a concise sequence has been developed for the rapid introduction of functionality found in the cytochalasin HIV protease inhibitor ( 1).

Molybdenum-mediated diastereoselective synthesis of 2-heterobicyclo[4.4.0]decene derivatives

The addition of a variety of functionalized zinc–copper reagents RCu(CN)ZnI 2 to (η5-cyclopentadienyl)(η4-cyclohexa-1,3-diene)dicarbonylmolybdenum cation 1 proceeds in a highly regio- and stereo-specific fashion to generate (η5-cyclopentadienyl)(π-allyl)dicarbonylmolybdenum complexes 3 with a functionalized side-chain at the C-4 position of the ring. Intramolecular cyclization of the (π-allyl)molybdenum complexes containing a pendant alcohol, carboxylic acid, thiol or amine functionality affords fused 2-heterobicyclo[4.4.0]decene derivatives.

ChemInform Abstract: Conjugate Addition Reactions of Functionalized Organozinc and Copper Reagents to (2‐Propynylidene)morpholinium Triflates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Addition of organocopper reagents to allylic acrylates — the preparation of γ, δ-unsaturated acids and subsequent functionalization to γ-lactones

Conjugate addition of monoorganocopper compounds with iodotrimethylsilane (TMSI) or lithium diorganocuprates, with or without halosilanes, to allylic acrylates give allylic silyl ketene acetals/ester enolates. These can undergo Claisen rearrangement to give diastereomeric mixtures of γ, δ-unsaturated acids after aqueous work-up. For organocuprates, the diastereomeric ratio is strongly affected by the halosilane. Either diastereomer can be obtained as major product by proper choice of copper reagent. Cyclization of the acids followed by reduction gives γ-lactones in good yields. A copper iodide/dimethyl sulfide complex is introduced as an excellent precursor to organocopper reagents.

Addition of functionalized zinc copper reagents to acetylenic esters: Synthesis of 2-carboalkoxy cyclohexenones

Conjugate addition of the zinc-copper reagent derived from ethyl 4-iodobutyrate to acetylenic esters in the presence of TMSCI and HMPA results in cyclization and formation of 3-alkyl-2-carboalkoxycyclohexenones in good yields.