Development of copper-mediated allylation of γ-activated-α,β-unsaturated lactam toward peptide mimetic synthesis

Reactions of γ-activated-α,β-unsaturated lactams with allylboronate in the presence of LiOi-Pr and CuX (stoichiometric or catalytic amount) proceed in an anti-S_N2′ manner to yield α-allylated compounds that serve as a potential synthetic intermediate for cis-aminoacyl-Pro mimetics.     

Reactivity of mixed organozinc and mixed organocopper reagents: 11. Nickel‐catalyzed atom‐economic aryl–allyl coupling of mixed (n‐alkyl)(aryl)zincs

Group selectivity in the allylation of mixed (n‐butyl)(phenyl)zinc reagent can be controlled by changing reaction parameters. CuCN‐catalyzed allylation in tetrahydrofuran (THF)–hexamethylphosphoric triamide is n‐butyl selective and also γ‐selective in the presence of MgCl₂, whereas CuI‐catalyzed allylation in THF in the presence of n‐Bu₃P takes place with a n‐butyl transfer:phenyl transfer ratio of 23:77 and an α:γ transfer ratio of phenyl of 76:24. NiCl₂(Ph₃P)₂‐catalyzed allylation in the presence of LiCl is phenyl selective with an α:γ ratio of 65:35. The reaction of methyl‐ or n‐butyl(aryl)zinc reagents with an allylic electrophile in THF at room temperature in the presence of NiCl₂(Ph₃P)₂ catalyst and LiCl as an additive provides an atom‐economic alternative to aryl–allyl coupling using diarylzincs. Copyright © 2014 John Wiley & Sons, Ltd.     

Palladium-catalyzed and samarium-promoted coupling of stereochemically-biased allylic acetates with carbonyl compounds

Stereochemically-biased bicyclic allylic acetates endo- and exo-1 were shown as being allyl donors for Pd-catalyzed carbonyl allylation using stoichiometric quantities of samarium diodide. Cyclopentenyl acetate and bicyclic derivatives 1 react with cyclic ketones in the presence of SmI₂ without requirement of palladium catalysis. Use of enantiomerically enriched substrate suggests that the reaction goes through a π-allyl samarium complex. However, this reactivity appears to be restricted to strained cyclopentenyl acetates since other linear and cyclic allylic acetates do not give the carbonyl allylation product.     

A new catalytic route to synthesis of silylgermylethynes

Silylgermylethynes known to be potential organometallic reagents and precursors of optoelectronic materials can be efficiently synthesized via a recently reported catalytic method called silylative coupling of alkynes with vinylsilicon compounds. The reaction of triethylethynylgermane with vinyltrisubstituted silanes catalyzed by [RuHCl(CO)(PR₃)_n] (where R = ⁱPr, Cy, Ph; n = 2-3) under optimal conditions selectively yields respective silylgermylethynes. Silylation of ethynylgermane with divinylsilicon derivatives such as siloxanes, silazanes, bis(silyl)benzene and bis(silyl)ethane gives monoethynylgermyl substituted vinyldisilicon products with high yields and selectivity, however, accompanied by traces of dialkynylgermyl derivatives. All catalytic results as well as those of stoichiometric study on the insertion of ethynylgermane into Ru-Si bond have permitted proposing mechanistic schemes of the reaction examined.     

Enantioselective allylation of aldehydes catalyzed by new bifunctional bisoxazoline-metal complexes

The asymmetric allylation reactions of aldehydes catalyzed by a 10 mol % bisoxazoline complex bearing a phosphine oxide moiety, which was newly designed and synthesized from l-serine, afforded the corresponding homoallylic alcohols in 48-74% yields with 39-86% ee. The reaction proceeds with the dual activation of the aldehyde and allylsilane by the Lewis acid and base of the catalyst. The evidence for the activation of the allylsilane was clarified by the ³¹P NMR spectra.     

A brief survey on the copper‐catalyzed allylation of alkylzinc and Grignard reagents under Barbier conditions

The same regioselectivity can be obtained in the CuI catalyzed allylic coupling of n‐butylzinc reagents prepared by either pre‐transmetallation or in situ transmetallation of Grignard reagents in the presence of allylic partner and catalyst. n‐Butylzinc bromide and di‐n‐butylzinc undergo γ‐selective allylation whereas tri‐n‐butylzincate gives preferential α‐selectivity. The regioselectivity obtained in the reaction of n‐butyl bromide and E‐crotyl chloride in the presence of Mg and CuCN is parallel to the coupling of preformed n‐butylmagnesium bromide. It is remarkable that the regiochemical outcome of copper catalyzed alkyl‐allyl coupling can be controlled by using Grignard reagents prepared under Barbier conditions and alkylzincs prepared by in situ transmetallation. Copyright © 2006 John Wiley & Sons, Ltd.     

Gallium-mediated allyl transfer from bulky homoallyl alcohol to aldehydes or alkynes: Control of dynamic σ-allylgalliums based on retro-allylation reaction

A new method for the preparation and control of dynamic σ-allylgalliums is disclosed. Upon treatment with a Grignard reagent and gallium trichloride, bulky homoallyl alcohols undergo gallium-mediated retro-allylation reaction to provide σ-allylgallium reagents. The σ-allylgallium reagents generated were applied to carbonyl allylation. The retro-allylation reaction generates (Z)- and (E)-σ-crotylgalliums stereospecifically, starting from erythro- and threo-homoallyl alcohols, respectively. The stereochemically defined crotylgallium reagents effected stereoselective allylation of aldehydes. Allylgallation reaction of alkynes with the allylgallium reagents prepared by retro-allylation is also described.     

Rapid access to homoallylic alcohols via Pd(OAc)2 catalyzed Barbier type allylation in presence of DMAP

DMAP was found to accelerate significantly the rate of Pd(OAc)₂ catalyzed Barbier type allylation of carbonyl compounds by allylbromide using SnCl₂·2H₂O as reducing agent. Both aldehyde as well as ketones produced excellent yields within a short reaction time in the presence of 3 mol % of Pd(OAc)₂ and 12 mol % of DMAP at room temperature. Aldehydes could be allylated within 5–10 min whereas, in case of ketones, the reaction completes in 45–120 min.     

Regioselectivity in Lewis acids catalyzed X-H (O, S, N) insertions of methyl styryldiazoacetate with benzyl alcohol, benzyl thiol, and aniline

Different from Rh(II) catalysts, X-H (X = O, S, N) insertion of methyl styryldiazoacetate catalyzed by Lewis acids including Cu(I), Cu(II) and Ag(I) complexes occurred at γ-position preferably. Only (E)-isomer was observed in the reactions. This method provides an alternative for the synthesis of γ-hydroxyl or γ-amino acid derivatives.     

The preparation of HCF2CdX and HCF2ZnX via direct insertion into the carbon halogen bond of CF2HY (Y = Br, I)

The difluoromethylcadmium and zinc reagents have been prepared in DMF via direct insertion of Cd⁰ into the carbon halogen bond of CF₂HY (Y = Br, I). These reagents are stable at 65-75 °C and exhibit prolonged stability and activity at room temperature. Metathesis of the difluoromethylcadmium reagents with Cu(I)X (X = Br, Cl) at −55 °C rapidly produces difluoromethylcopper. The copper reagent is significantly less stable than the cadmium or zinc reagent and rapidly decomposes at room temperature. The difluoromethylcadmium and copper reagents exhibit good reactivity with allylic halides, propargylic derivatives and 1-iodoalkynes to provide good yields of the corresponding difluoromethylalkenes, difluoromethylallenes and difluoromethyl-2-alkynes. Alkylation is successful only with reactive alkyl halides. Generally, the difluoromethylcopper reagent is more reactive than the difluoromethylcadmium reagent and generally exhibits higher regioselectivity in reactions that can occur by either α- or γ-attack.     

Catalytic enantioselective allylation of aldehydes using β-amido functionalized allylstannanes with chiral In(OTf)3/i-Pr-pybox complexes

The enantioselective allylation of aldehydes using a variety of β-amido functionalized allyltributylstannanes proceeded smoothly with good to high yields and enantioselectivities in the presence of 10 mol % of a chiral catalytic complex prepared from In(OTf)₃ and 2,6-bis[(S)-4-isopropyloxazolin-2-yl]pyridine {(S)-i-Pr-pybox}, providing the corresponding chiral γ-hydroxy amides.     

Allylation of prochiral C-nucleophiles catalyzed by the Pd(0)—(<Emphasis Type="Italic">S</Emphasis>)-(—)-BINAP complex

The allylation of prochiral C-nucleophiles catalyzed by the Pd(0)—(S)-(—)-BINAP complex (BINAP is 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) was studied. The enantioselectivity of the allylation was found to be low. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1753—1755, August, 2008.     

Reactivity of γ-chloro-gem-trichloroalkanes with chromous chloride

CrCl₂-mediated condensation of γ-chloro-gem-trichloroalkanes with aldehyde generates homoallylic alcohols through a hydride rearrangement followed by a Nozaki-Hiyama allylation.     

Highly selective flow injection spectrophotometric determination of gold based on its catalytic effect on the oxidation of variamine blue by potassium iodate in aqueous N,N-dimethylformamide medium

A highly selective and simple flow injection method is reported for the determination of Au(III) in jewel samples. The method is based on the catalytic effect of Au(III) on the oxidation of 4-amino-4′-methoxydiphenylamine hydrochloride (Variamine Blue B base, VB) by KIO₃. The colored reaction product was monitored spectrophotometrically at 546 nm. A volume fraction of 40% N,N-dimethylformamide (DMF) greatly enhances the selectivity of the method. The chemical (pH and concentrations of reagents) and instrumental variables (sample injection volume, reagents flow rates, reaction coil length) affecting the determination were studied and optimized. Under the selected values, the analyte could be determined in the range of 0.1-12.0 mg L⁻¹ (r = 0.9997), at a sampling rate of 120 h⁻¹. The proposed assay was precise (s_r = 0.8% at 5.0 mg L⁻¹ Au(III), n = 12) and adequately sensitive with a 3σ limit of detection of 0.03 mg L⁻¹. The method was successfully applied to the analysis of jewel samples. The obtained results were favorably compared to flame atomic absorption spectrometry (FAAS) used as a reference method.     

Ru3(CO)12-catalyzed intramolecular allylic transfer reaction of tethered carbonyl group and allylic acetate moiety

A ruthenium catalyzed intramolecular allylic transfer reaction of allylic acetates containing aldehydes or ketones to form cis-homoallylic cyclopentanols and cyclohexanols as a major component is described. The use of Ru₃(CO)₁₂ (1 mol %) to promote reaction results in a convenient procedure for intramolecular allylation of carbonyl functionalities.     

Mechanism of olefin hydrosilylation catalyzed by [RuCl(NCCH3)5]: A DFT study

The hydrosilylation reaction between methyldimethoxysilane and methylvinyldimethoxysilane, catalyzed by the cationic species chloropenta(acetonitrile)ruthenium(II)⁺ (C1), was investigated with density functional theory (DFT). The Chalk-Harrod, Glaser-Tilley and σ-bond metathesis mechanisms were considered as mechanistic possibilities for the reaction and enthalpy profiles of each pathway were computed for the active form of C1. In contrast to the commonly accepted Chalk-Harrod mechanism of hydrosilylation, the computational results indicate that a σ-bond metathesis mechanism, involving the formation of a hydride analogue of C1, is most favored. The B3LYP calculated activation enthalpy for this pathway (ΔH_act = 13.1 kcal/mol) is consistent with the experimental observation that C1 is a reasonable catalyst for this reaction under the applied experimental conditions.     

Synthesis of α- and β-C-glycosides of N-acetylglucosamine

As part of efforts to make available new classes of bioactive C-glycoconjugates, d-glucosamine has been effectively converted into a series of 2-deoxy-2-amino-C-glycosides. This versatile approach is keyed by a remarkably effective metal catalyzed olefin isomerization of the isomeric C-allyl amino sugars which, in turn, are readily available via radical allylation of d-glucosamine.     

1-(2-Formamidoethyl)-3-phenylurea functionalized activated carbon for selective solid-phase extraction and preconcentration of metal ions

A novel method that utilizes 1-(2-formamidoethyl)-3-phenylurea-modified activated carbon (AC-1-(2-formamidoethyl)-3-phenylurea) as a solid-phase extractant has been developed for simultaneous preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) prior to the measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). Experimental conditions for effective adsorption of trace levels of Cr(III), Cu(II), Fe(III) and Pb(II) were optimized using batch and column procedures in detail. The optimum pH value for the separation of metal ions simultaneously on the new sorbent was 4. And the adsorbed metal ions could be completely eluted by using 2.0 mL 2.0 mol L⁻¹ HCl solution. Common coexisting ions did not interfere with the separation and determination of target metal ions. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 39.8, 39.9, 77.8 and 17.3 mg g⁻¹ for Cr(III), Cu(II), Fe(III) and Pb(II), respectively. The detection limits of the method were found to be 0.15, 0.41, 0.27 and 0.36 ng mL⁻¹ for Cr(III), Cu(II), Fe(III) and Pb(II), respectively. The relative standard deviation (RSD) of the method was lower than 4.0% (n = 8). The method was successfully applied for the preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) in natural and certified samples with satisfactory results.     

Concise synthesis of trans- and cis-3,4-disubstituted piperidines based on regio- and stereoselective allylation of cyclopentenyl esters

3,4-Disubstituted piperidines were synthesized through anti S_N2′ allylation of 4-substituted 2-cyclopentenyl esters with reagents based on RMgX and CuX, thus allowing equal access to both trans- and cis-isomers. As an application, the paroxetine intermediate was synthesized efficiently. During the investigation, the MeOCH₂CO₂ group was found to show high reactivity in the pivotal anti S_N2′ type reaction using the reagent derived from (i-PrO)Me₂SiCH₂MgCl and CuCN.     

Novel iodine catalyzed diastereoselective synthesis of trans-2,6-disubstituted tetrahydro-2H-pyrans: synthesis of C1–C13 fragment of bistramide-A

A new method for the stereoselective synthesis of trans 2.6-disubstituted tetrahydro-2H-pyrans has been developed involving iodine catalyzed allylation of tetrahydro-2H-pyranol with excellent trans selectivity. The method was also applied toward the construction of C1–C13 fragment of bistramide-A in 11 steps with 21.4% overall yield.