Showing papers on "Nucleophile published in 1997"
Book•
01 Jan 1997
TL;DR: In this article, the authors present a list of metal-mediated reaction types for industrial applications: transition-metal-catalyzed reactions, nucleophilic additions and substitutions, pericyclic reactions, and Oxidations and reductions.
Abstract: Pericyclic Reactions. Nucleophilic Additions and Substitutions. Metal-- Mediated Reactions. Transition--Metal--Catalyzed Reactions. Oxidations and Reductions. Industrial Applications. Index.
850 citations
465 citations
TL;DR: In this article, a review of solid-phase organic reactions performed on solid supports is presented in a graphical abstract format and examples are given of the following reactions: amide formation, aromatic substitution (nucleophilic/electrophilic), cleavage, condensation, cycloaddition, deprotection/protection, Grignard and related reactions.
335 citations
199 citations
197 citations
TL;DR: The syntheses, characterizations, and X-ray crystallographic structure determinations are described for adducts of stable nucleophilic carbenes with pnictinidenes, and the (31)P NMR shifts of the phosphorusAdducts suggest strongly shielded phosphorus centers in accord with the polarized structures.
Abstract: The syntheses, characterizations, and X-ray crystallographic structure determinations are described for adducts of stable nucleophilic carbenes with pnictinidenes. The adducts between 1,3-dimesitylimidazol-2-ylidene and phenylphosphinidene, phenylarsinidene, (trifluoromethyl)phosphinidene, and (pentafluorophenyl)arsinidene are reported. These carbene-pnictinidene adducts are formed by the direct reaction of a stable nucleophilic carbene with the corresponding pnictinidene cyclic oligomers. The synthesis and structure of the adduct between 1,3-dimesitylimidazolin-2-ylidene and phenylphosphinidene from the reaction of 1,3-dimesitylimidazolin-2-ylidene with phenylphosphorus dichloride are also reported. These carbene-pnictinidene adducts possess strongly polarized pnictinidene-carbene bonds. The C-Pn-C angles are all typically small at 97-102 degrees, and there is only a 4% shortening of the nominal Pn=C double bond compared to the Pn-C single bond to the second substituent on the pnictogen. The (31)P NMR shifts of the phosphorus adducts suggest strongly shielded phosphorus centers in accord with the polarized structures.
174 citations
129 citations
TL;DR: In this paper, a high-yield, one-step synthesis of 2-deoxy-2-fluoro sugars and their glycosides from glycals using the available electrophilic fluorination reagent 1-chloromethyl-4-fluor-1,4-diazoniabicyclo[2.2]octane bis(tetrafluoroborate) (Selectfluor) in the presence of a nucleophile was described.
Abstract: This paper describes a high-yield, one-step synthesis of 2-deoxy-2-fluoro sugars and their glycosides from glycals using the available electrophilic fluorination reagent 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor) in the presence of a nucleophile. The method was further expanded to the synthesis of glycosyl fluorides and glycosides from anomeric hydroxy or thioglycoside derivatives.
128 citations
TL;DR: In this paper, preferential reactions of aldimines over aldehydes in nucleophilic additions using a lanthanide salt as a Lewis acid catalyst was described, and it is well-recognized that aldinines are less reactive than aldehides toward nucleophoric additions.
Abstract: It is well-recognized that aldimines are less reactive than aldehydes toward nucleophilic additions In this paper, an unprecedented change in the reactivity is described: preferential reactions of aldimines over aldehydes in nucleophilic additions using a lanthanide salt as a Lewis acid catalyst In the presence of a catalytic amount of ytterbium triflate (Yb(OTf)3), only aldimines reacted with silyl enol ethers, ketene silyl acetals, allyltributylstannane, or cyanotrimethylsilane to afford the corresponding adducts in high yields, even in the coexistence of aldehydes Selective formation of an aldimine−Yb(OTf)3 complex rather than an aldehyde−Yb(OTf)3 complex was indicated by 13C NMR analyses While this report demonstrates the effective use of Lewis acids in organic synthesis, the basic idea of changing reactivity as shown here will be widely applied to many other nucleophilic additions
117 citations
TL;DR: In this article, the kinetics of the reaction of a series of aromatic and aliphatic thiols with cluster 1 were determined, and the rate determining step of the desulfurization reaction is the initial association of the thiol to the cluster.
Abstract: The kinetics of the reaction of a series of aromatic and aliphatic thiols with cluster 1 were determined. These reactions form cluster 2 and the arene or alkane corresponding to the thiol: Cp‘2Mo2Co2S3(CO)4 (1) + RSH → Cp‘2Mo2Co2S4(CO)2 (2) + RH + 2CO. These reactions are first order in thiol and first order in cluster 1 with appreciable negative entropies of activation. These data suggest that the rate determining step of the desulfurization reaction is the initial association of the thiol to the cluster. The more nucleophilic thiolate anions react with 1 at −40 °C to form an adduct in which the thiolate anion is bound η1 to the Co atom. At −25 °C, the initial adduct rearranges to a fluxional μ2, η1-bound thiolate. The fluxional process is proposed to involve a concerted “walking” of the thiolate and a μ2-bound sulfide ligand on the surface of the cluster. Near 35 °C, the thiolate−cluster adduct undergoes C−S bond homolysis to give the paramagnetic anion of cluster 1 and the phenyl or alkyl radical. The...
112 citations
TL;DR: A review of the methods available for the synthesis of C-glycosides that involve the use of carbohydrate units expressing nucleophilic reactivity at C(1) (the anomeric site) is given in this article.
Abstract: This chapter reviews the methods available for the synthesis of C-glycosides that involve the use of carbohydrate units expressing nucleophilic reactivity at C(1) (the anomeric site). A wide variety of “anionic” (organometallic derivatives) and neutral (free radical) C(1) nucleophiles are known and examples of all structural types are presented. Coverage includes methods for generating effective C(1)-nucleophiles, their reactivity and utility in C-glycoside synthesis and, where appropriate, any associated limitations.
TL;DR: In this paper, the enantiodetermination step is assumed to be nucleophilic attack of a nitrogen nucleophile on a π-allyl palladium intermediate, and the stereoselectivity is strongly influenced by the structure of the chiral phosphine ligands and substrates, as well as by reaction conditions.
Abstract: Cycloaddition reaction of 2-vinyloxiranes with carbodiimides using Pd2(dba)3·CHCl3, and TolBINAP as the chiral ligand, in THF at ambient temperature, afforded 4-vinyl-1,3-oxazolidin-2-imines in 70−99% yield and in up to 95% ee. The stereoselectivity is strongly influenced by the structure of the chiral phosphine ligands and substrates, as well as by the reaction conditions. The enantiodetermination step is assumed to be nucleophilic attack of a nitrogen nucleophile on a π-allyl palladium intermediate. Reaction of 2-vinyloxiranes with isocyanates using the same catalyst system afforded 4-vinyl-1,3-oxazolidin-2-ones in high yield but in no greater than 50% ee.
TL;DR: In this article, it was shown that the primary nosylamide adducts can be readily cleaved under mild conditions to provide the primary amines, without competing attack on the nosyl functionality (S n Ar).
TL;DR: In this paper, the cation radicals of benzyltrialkylsilanes have been generated using photoinduced electron transfer and characterized using transient absorption spectroscopy. Absolute rate constants for nucleoph...
Abstract: The cation radicals of benzyltrialkylsilanes have been generated using photoinduced electron transfer and characterized using transient absorption spectroscopy. Absolute rate constants for nucleoph...
TL;DR: In this article, values in DMSO are reported for ammonium ions derived from amines which have been widely used as nucleophiles in nucleophilic substitution reactions; values are also given for four different types of amines used as indicators.
Abstract: pK a
Values in DMSO are
reported for ammonium ions derived from amines which have
previously been widely used as nucleophiles in nucleophilic
aromatic substitution reactions; values are also given for four
polynitrodiphenylamines used as indicators
TL;DR: Quantitative mechanical/molecular mechanical calculations of the pathway of acetyl‐CoA enolization within citrate synthase support the identification of Asp‐375 as the catalytic base, and His‐274, the proposed general acid, is found to be neutral.
Abstract: Citrate synthase forms citrate by deprotonation of acetyl-CoA followed by nucleophilic attack of this substrate on oxaloacetate, and subsequent hydrolysis. The rapid reaction rate is puzzling because of the instability of the postulated nucleophilic intermediate, the enolate of acetyl-CoA. As alternatives, the enol of acetyl-CoA, or an enolic intermediate sharing a proton with His-274 in a “low-barrier” hydrogen bond have been suggested. Similar problems of intermediate instability have been noted in other enzymic carbon acid deprotonation reactions. Quantum mechanical/molecular mechanical calculations of the pathway of acetyl-CoA enolization within citrate synthase support the identification of Asp-375 as the catalytic base. His-274, the proposed general acid, is found to be neutral. The acetyl-CoA enolate is more stable at the active site than the enol, and is stabilized by hydrogen bonds from His-274 and a water molecule. The conditions for formation of a low-barrier hydrogen bond do not appear to be met, and the calculated hydrogen bond stabilization in the reaction is less than the gas-phase energy, due to interactions with Asp-375 at the active site. The enolate character of the intermediate is apparently necessary for the condensation reaction to proceed efficiently. Proteins 27:9–25 © 1997 Wiley-Liss, Inc.
TL;DR: Alkenylidenes undergo regio-and stereoselective intramolecular CH insertion reactions that are excellently suited for the synthesis of cyclopentenes as discussed by the authors.
Abstract: Alkenylidenes R2CC: (= alkylidene carbenes) undergo regio- and stereoselective intramolecular CH insertion reactions that are excellently suited for the synthesis of cyclopentenes The 1, 2-shifts occurring with RH and RAr are useful for the preparation of alkynes Alkenylidenes are efficiently generated from carbonyl compounds by diazomethylation, from vinyl halides by α-elimination, from alkynyliodonium salts by addition of nucleophiles, and from alkynes by retro-1, 2-shifts Specific applications of the various methods, particularly in the synthesis of natural products, are discussed
TL;DR: A palladium-phosphine complex was designed and prepared on polyethylene glycol-polystyrene graft copolymer (PEG-PS) resins as discussed by the authors.
TL;DR: The polymeric reagent 4 was shown to be particularly suitable for the high throughput parallel synthesis of amides libraries, and could be attributed to its high acidity, conferred by the sulfonyl moiety.
Abstract: The synthesis of a new polymer-supported coupling reagent derived from 1-hydroxybenzotriazole is described. An aminomethylated polystyrene was functionalized by reaction with 3-nitro-4-chlorobenzenesulfonyl chloride (2) followed by treatement with hydrazine hydrate, to give the polymeric N-benzyl-1-hydroxybenzotriazole-6-sulfonamide (4).The polymeric reagent 4 was shown to be highly efficient for the synthesis of amides. The efficiency of 4 could be attributed to its high acidity, conferred by the sulfonyl moiety. The procedure for amide synthesis involves the formation of an activated ester on the derivatized polymer followed, in a second step, by treatment with an amine to generate the amide in solution. Simple filtration allows the separation of the product from the polymeric reagent which in this case plays the role of leaving group. An optimization study of this two-step procedure was performed. As amides are obtained in solution free of reaction byproducts, this method can be used in an automated pr...
TL;DR: In this article, the divalent metal ion-catalyzed hydrolysis of thionate (PS) and oxonate (PO) organophosphorus pesticides has been examined in light of three possible catalysis mech anisms: (1) metal ion coordination of the thionates or oxonates oxygen to enhance the electrophilicity of the phosphorus electrophilic site; (2) ion coordination and induced deprotonation of water to create a reactive nucleophile.
Abstract: The divalent metal ion-catalyzed hydrolysis of thionate (PS) and oxonate (PO) organophosphorus pesticides has been examined in light of three possible catalysis mech anisms: (1) metal ion coordination of the thionate sulfur or oxonate oxygen to enhance the electrophilicity of the phosphorus electrophilic site; (2) metal ion coordination and induced deprotonation of water to create a reactive nucleophile; and (3) metal ion coordination of the leaving group to facilitate its exit. The effect of the following metals at a concentration of 1 mM was examined: CoII, NiII, CuII, ZnII, and PbII. These metal ions were chosen for their ability to complex organic ligands and inorganic nucleophiles. Of these metal ions, CuII possesses properties most suitable for all three catalytic mechanisms and serves as the most effective catalyst for the five thionate esters (chlorpyrifos-methyl, zinophos, diazinon, parathion-methyl, and ronnel) and the two oxonate esters (chlorpyrifos-methyl oxon and paraoxon) included in this...
TL;DR: In this paper, the steric interactions between the R2 group and the equatorial chloride atom, leading to out-of-plane bending of the chloride atom were studied. And the angle between the NNN plane and the RhCl axis is 5.34° for 7, 11.73° for 8, and 10.04° for 12.
TL;DR: In this article, the reactivity of (1-alkyny1) carbene complexes is discussed, especially if a regio-and/or stereoselective formation of C,C- or C,X bonds is achieved that might be utilized in organic synthesis.
Abstract: Publisher Summary This chapter focuses on the reactivity of (1-alkyny1)carbene complexes, especially if a regio- and/or stereoselective formation of C,C- or C,X bonds is achieved that might be utilized in organic synthesis. Typical modes for the preparation of (1-alkyny1)carbene complexes, as well as spectroscopic and structural data, are summarized. The addition of a carbon nucleophile to a (1-alkynyl)carbene complex occurs either at the M=C or at the C=C bond. However, by the reaction of (1-alkyny1)carbene complexes with nitrogen- or phosphorus-containing compounds products, such as (enamino)carbene and (enphosphino)carbene complexes are made available. The chapter also outlines the reaction of (1-alkyny1)carbene complexes with oxygen and sulfur nucleophiles and discusses the 1-alkynyl acylmetallates. Because of the highly unsaturated character of (1-alkyny1)carbene complexes, a variety of metal π-complexes can be derived from the coordination of the M=C as well as of the C≡C bonds. Fischer carbyne complexes are generated from carbene complexes by 1,2 elimination of an alcohol under the influence of boron trihalides or other Lewis acids.
TL;DR: In this paper, the synthesis, structural characterization, and reactivity of tantalum complexes with chelating imido−amido ligands are reported, and the crystal structure of 9 was determined.
Abstract: The synthesis, structural characterization, and reactivity of tantalum complexes with chelating imido−amido ligands are reported. The highly bent imido Cp* = η5-C5Me5), with a TaN−C bond angle of 116.3(4)°, was synthesized from Cp*TaCl4 and the lithiated bis(silylamino)biphenyl (C6H3Me)2(NLiSiMe3)2 (3). Compound 4 undergoes reactions with electrophiles at the nucleophilic imido nitrogen atom. The methyl reacts with xylyl isonitrile to give an insertion product, 6, which was structurally characterized. Addition of MeI to 5 gives a cationic diamide tantalum the ionic structure of which was confirmed by X-ray crystallography. Reactions of 4 and 5 with unhindered silanes result in addition of the silane Si−H bond across the TaN double bond. Addition of PhSiH3 to 4 and 5 gave the respectively. The crystal structure of 9 was determined. Compounds 8 and 9 are unstable and decompose via elimination of HSiMe3. In the presence of CH2Cl2 and PhSiH3, 4 was slowly converted to another hydrido A mechanism for this tran...
TL;DR: In this article, the synthesis and structures of [8,8]-μ-(OSO2O)(1,2-C2B9H10)2-3-Co]-and [(8-Ph-1, 2-C 2B9h10)-3-co-(1',2'-C 2b9H11]- ions are described.
Abstract: Syntheses and structures of [8,8'-μ-(OSO2O)(1,2-C2B9H10)2-3-Co]-and [(8-Ph-1,2-C2B9H10)-3-Co-(1',2'-C2B9H11]- ions and of [(8-dioxane-1,2-C2B9H10)-3-Co-(1',2'-C2B9H11)] zwitterion are described. All compounds result on dimethyl sulfate induced nucleophilic B-substitution of the parent cobalta-carborane sandwich ion under acid catalysis. A general mechanism is proposed. Constitutions of all compounds are inferred from the mass and multinuclear NMR spectroscopy and all structures are established by X-ray diffraction. Selected NMR and X-ray data are presented.
TL;DR: In this paper, the synthesis of 2, 4, 6-trisubstituted pyrimidines on solid support was described, which combines efficiently solid-phase chemistry with a multicomponent reaction and a multidirectional cleavage step to form highly diverse pyridines in a parallel array.
Abstract: We describe a versatile novel approach for the synthesis of 2, 4, 6-trisubstituted pyrimidines on solid support. Thus, polymer-boun J thiouronium salt 2 reacted in high yield in a cyclocondensation reaction with the acetylenic ketones 3 to form, after tert-butyl-ester cleavage, the polymer-bound carboxylic acids 4, which were cleaved by oxidation with 3-chloroperbenzoic acid and pyrrolidine to form the 2-pyrrolidinylpyrimidine-4-carboxylic acids 6a-c in high yields and purities without further purification (Scheme 1). Alternatively, acid 4a was subjected to an Ugi four-component condensation which gave the polymer-bound Ugi products 9a-e in good yields (Scheme 2). Multidirectional cleavage reaction of sulfone 8a with different nucleophiles resulted in the clean formation of pyrimidine-4-carboxamides 10–13 (Scheme 3). This strategy combines efficiently solid-phase chemistry with a multicomponent reaction and a multidirectional cleavage step to form highly diverse pyrimidines in a parallel array.
TL;DR: In this article, the product distribution from nucleophilic attack on (η3-allyl)palladium complexes is analyzed by a combination of molecular mechanics and QSAR techniques.
TL;DR: In this article, the authors used 2-(1-hydroxyalkyl)-6-(4,5-dihydro-2-oxazolyl)pyridines and 2-( 1-alkoxyalkyl)6-( 4,5dihdroid-2oxazyl)-pyridine as ligands for palladium-catalyzed substitution.
Abstract: Highly enantioselective (up to >99% ee) palladium-catalyzed substitution of rac-3-diphenyl-2-propenyl acetate with dimethyl malonate as nucleophile was achieved using 2-(1-hydroxyalkyl)-6-(4,5-dihydro-2-oxazolyl)pyridines and 2-(1-alkoxyalkyl)-6-(4,5-dihydro-2-oxazolyl)pyridines as ligands for palladium. The selectivity was found to be highly dependent on the nature of the substituents on the ligand and on the relative configuration of the two stereogenic centers present in the ligand. The results are discussed in terms of the conformation of the ligands in the intermediate π-allylpalladium complexes.
TL;DR: In this article, the aminolysis reactions of phenyl dithioacetates with anilines, N,N-dimethylanilines (DMA), and benzylamines (BA) in acetonitrile were investigated.
Abstract: The aminolysis reactions of phenyl dithioacetates with anilines (AN), N,N-dimethylanilines (DMA), and benzylamines (BA) in acetonitrile are investigated. The mechanism is relatively simple, involving a zwitterionic tetrahedral intermediate, T±, and is uncomplicated by the fast proton transfer step which may become rate limiting in the aminolysis of thiono and dithio esters and carbonates with poor leaving groups in water. The mechanism changes from rate-limiting expulsion of the leaving group with βX = 0.80−0.86 and βZ = −0.71 to −0.84 for ANs and DMAs to rate-limiting attack by the nucleophile with much smaller magnitudes of βX and βZ for BAs. The relatively large βXZ values for the former series and a smaller βXZ for the latter series support the proposed mechanistic change.
TL;DR: In this article, the physicochemical properties of proton transfer between the thiol group of the protein tyrosine phosphatase and a substrate phosphate oxygen atom have been studied using free energy perturbation simulations.