Mechanism of remote conjugate addition of a lithium organocuprate to a polyconjugated carbonyl compound.
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Biomedical subjects
Eiichi Nakamura
Publications and source records attributed to Eiichi Nakamura.
Indium triflate-catalyzed vinylation of beta-ketoesters with acetylene gas.
[reaction: see text]. An In(OTf)(3)-catalyzed addition of a beta-ketoester to acetylene in the presence of molecular sieves produces a alpha-vinylated ketoester in good to excellent yield. The vinylation reaction proceeds without any loss of elements in starting molecules under solvent-free conditions and allows the use of welding-grade acetylene, providing a practical method for synthetic utilization of acetylene gas.
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Synergistic dimetallic effects in propargylic substitution reaction catalyzed by thiolate-bridged diruthenium complex.
The origin of unique catalytic activity of a thiolate-bridged diruthenium complex in nucleophilic substitution reactions of propargylic alcohols, which features a diruthenium-allenylidene complex as a key intermediate, was studied with the aid of density functional calculations (B3LYP). Comparison of mono- and diruthenium systems has shown that the rigid but reasonably flexible Ru-Ru core structure plays a critical role in the catalyst turnover step (i.e., dissociative ligand exchange of the product pi-complex with the starting propargyl alcohol that goes through a coordinatively unsaturated Ru complex). In the diruthenium system, the energy loss due to coordinative unsaturation can be compensated by reinforcement of the Ru-Ru bond, while such an effect is unavailable in the monoruthenium counterpart. Weaker back-donation ability of the diruthenium complex is also advantageous for dissociation of the pi-complex. Thus, ligand exchange takes place smoothly in the diruthenium system to regenerate the reactive species, while the monoruthenium reaction stops at a dead-end Ru product pi-complex. The present studies have also shown the important role of protic molecules (e.g., MeOH) that mediate smooth proton transfer in the propargyl alcohol-allenylidene transformation.
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Ball-and-socket stacking of supercharged geodesic polyarenes: bonding by interstitial lithium ions.
Unprecedented supramolecular stacks of highly reduced geodesic pi-systems were prepared by the reduction of the derivatized fullerenes Me(5)C(60)H and Ph(5)C(60)H and corannulene with lithium metal (R(5)C(60)(5)(-)/Cor(4)(-)/9Li(+)). The host--guest assemblies form because of the enhanced electrostatic interactions between the lithium cations and the anionic moieties, in addition to the structural compatibility between the curved hydrocarbons. The high stability of these new supramolecular assemblies (heterodimers) enables the introduction of another organization motif to the system. This is achieved by using tethered corannulenes as host molecules, which leads to the formation of tethered bis-heterodimers ((Me(5)C(60)(5)(-)/Cor(4)(-))(2)(CH(2))(8)/18Li(+)).
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Syntheses, structure, and derivatization of potassium complexes of penta(organo)[60]fullerene-monoanion, -dianion, and -trianion into hepta- and octa(organo)fullerenes.
Two-electron reduction of penta(organo)[60]fullerenes C(60)Ar(5)H (Ar = Ph and biphenyl) by potassium/mercury amalgam afforded potassium complexes of the corresponding open-shell radical dianions [K+(thf)n]2[C60Ar5(2-.)]. These compounds were characterized by UV-visible-near-IR and electron spin resonance spectroscopy in solution. Anaerobic crystallization of [K+(thf)n]2[C60(biphenyl)(5)(2-.)] that exists largely as a monomer in solution gave black crystals of its dimer [K+(thf)3]4[(biphenyl)5C60-C60(biphenyl)5(4-)], in which the two fullerene units are connected by a C-C single bond [1.577(11) A] as determined by X-ray diffraction. Three-electron reduction of C60Ar5H with metallic potassium gave a black-green trianion [K+(thf)n]3[C60Ar5(3-)]. The reaction of the trianion with an alkyl halide RBr (R = PhCH(2) and Ph(2)CH) regioselectively afforded a hepta-organofullerene C60Ar5R2H, from which a potassium complex [K+(thf)n][C60(biphenyl)5(CH2Ph)(2)(-)] and a palladium complex Pd[C60(biphenyl)5(CH2Ph)2](pi-methallyl) as well as octa-organofullerene compounds C60(biphenyl)5(CH2Ph)3H2 and Ru[C60(biphenyl)5(C2Ph)3H]Cp were synthesized. These compounds possess a dibenzo-fused corannulene pi-electron conjugated system and are luminescent.
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Regioselective oxygenative tetraamination of [60]fullerene. Fullerene-mediated reduction of molecular oxygen by amine via ground state single electron transfer in dimethyl sulfoxide.
The reaction of [60]fullerene with a variety of a secondary aliphatic amines in 20% v/v dimethyl sulfoxide in chlorobenzene under an atmospheric pressure of molecular oxygen allows regioselective introduction of four amino groups and one epoxide group around one pentagon of the fullerene molecule in good to high yield. This new synthesis of tetraaminofullerene expoxide can be carried out with a simple procedure on a multigram scale at room temperature and affords a variety of functionalized fullerene derivatives. Near-infrared analysis of a mixture of [60]fullerene and piperidine in a deaerated dimethyl sulfoxide/chlorobenzene mixture indicated equilibrium formation of [60]fullerene radical anion (C60*-) that persists at least for 2 weeks at room temperature but reacts immediately with molecular oxygen to give the tetraaminofullerene expoxide. The Benesi-Hildebrand analysis of the concentration dependency of the near-infrared absorption indicated that a [C60*- piperidine*+] radical ion pair is formed with an equivalent constant of K = 0.62 +/- 0.02 M(-1) at 25 degrees C. This and other lines of evidence suggest that the oxygenative amination reaction involves C60-mediated reduction of molecular oxygen by the amine.
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Ultra-rapid synthesis of 15O-labeled 2-deoxy-D-glucose for positron emission tomography (PET).
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Animals↗
Thermodynamic and kinetic control in selective ligand transfer in conjugate addition of mixed organocuprate Me(X)CuLi.
Since the proposal of the dummy ligand concept by Corey, it has been widely accepted that the ligand transfer selectivity of a mixed organocuprate (Me(X)CuLi) depends on the Cu-X bond strength. The present B3LYP density functional studies on the Me(2)(X)Cu(III).OMe(2), pi-allyl Cu(III), and Me(X)Cu(III)LiCl.LiCl reacting with acrolein showed that the ligand transfer selectivity of the conjugate addition depends on two factors, thermodynamic stability (X = tert-butyl, ethynyl, cyano, and thiomethyl groups) and kinetic reactivity ((trimethylsilyl)methyl and vinyl groups) of the Cu(III) intermediate formed by complexation of the cuprate and the alpha,beta-unsaturated carbonyl compound. For the typical dummy ligands (X = alkynyl, cyano, and heteroatom ligands), the trans effect and the strong Li-X affinity are the reasons why these ligands stay on the copper atom. In contrast, for the (trimethylsilyl)methyl and vinyl groups, the selectivity depends on the kinetics of reductive elimination of the Cu(III) intermediate. The (trimethylsilyl)methyl transfer is retarded by repulsive four-electron interaction between the lone pair Cu 3d(xy)() orbital and the C-Si sigma-orbital.
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Reactivity and stability of organocopper(I), silver(I), and gold(I) ate compounds and their trivalent derivatives.
Organocuprate (R(2)Cu(-)) reagents react with a carbon electrophile to form a new C-C bond, yet their silver and gold counterparts seldom serve for such purposes. The origin of this striking difference is discussed with the aid of the quantum mechanical calculations using hybrid density functional method. The copper reaction takes place through two steps, the nucleophilic reaction of the ate complex R(2)Cu(I)(-) with an electrophile E(+) and the decomposition of the resulting R(2)(E)Cu(III) intermediate. These two steps were examined for Cu, Ag, and Au to find the reasons for the superiority of organocopper compounds to the silver and the gold counterparts. The first reaction is favored because of the higher-lying d-orbitals that directly participate in the nucleophilic reaction. The second reaction is faster with copper because of the intrinsic instability of the high valent copper species.
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Supramolecular modulation of action of polyamine on enzyme/DNA interactions.
Thread-in-hole complexation of cucurbit[6]uril (CB[6]) with spermidine and spermine either enhances or reduces the activity of the polyamine on the enzymatic reactions of DNA.
Biogenic Polyamines↗
Measurement of total and differential white blood cell counts in synovial fluid by means of an automated hematology analyzer.
We developed a rapid and accurate method for quantifying total and differential white blood cell (WBC) counts by pretreating synovial fluid with hyaluronidase and using an automated hematology analyzer. Forty-seven samples of synovial fluid that had been placed in blood-collection tubes containing ethylenediamine- N,N,N',N' -tetraacetic acid as an anticoagulant were treated with hyaluronidase at 37 degrees C for 10 minutes, and then the total and differential WBC counts were determined by means of the automated hematology analyzer. Results were compared with those achieved by traditional manual counting methods. For the automated method, the coefficient of variation values for within-run precision of the WBC count were 5.27%, 3.56%, and 3.01% at 0.54, 1.12, and 2.05 x 10(9) /L, respectively; the run-to-run coefficient of variation values was less than 10.0%. The total and differential WBC counts obtained by this automated method showed good correlation with those obtained by the hemocytometer method ( r = .998; P < .0001; regression formula, y = 0.986 x - 0.072). Bland-Altman plots indicated no significant discrepancy between the methods. Our evaluation supports the use of this automated hematology analyzer method to measure total and differential WBC counts, which should aid clinical diagnosis.
Arthritis, Infectious↗
Stereoselective synthesis of tetra-substituted olefins via addition of zinc enolates to unactivated alkynes.
[reaction: see text] In the presence of a stoichiometric or catalytic amount of diethylzinc, a beta-aminocrotonamide undergoes sequential addition/isomerization reactions with 1-alkyne to produce, upon hydrolysis, an alpha-alkylidene beta-dicarbonyl compound in a highly stereoselective manner. The method complements the conventional Knoevenagel synthesis of this class of compounds as to the choice of the starting material and the scope and stereochemistry of the product.
Alkenes↗
Enantioselective allylic substitution of cinnamyl esters catalyzed by iridium-chiral aryl phosphite complex: conspicuous change in the mechanistic spectrum by a countercation and solvent.
Iridium-catalyzed asymmetric allylic alkylation of monoaryl substrates 4-6 with chiral phosphites 1-3 has been investigated. Although branched isomers were formed with high regioselectivities, the enantioselectivities of these products were remarkably influenced by solvents, countercations, and additives (ZnCl(2) and LiCl).
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Sequential coupling of zincated hydrazone, alkenylboronate, and electrophile that creates several contiguous stereogenic centers.
A zincated N,N-dimethylhydrazone of a ketone undergoes stereospecific syn addition to E- or Z-alkenylboronate to generate a gamma-Zn/B dimetallic intermediate, which reacts with a carbon electrophile to give a gamma-borylhydrazone in good yield with excellent diastereoselectivity, creating two to four contiguous stereogenic centers in a one-pot reaction.
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L-shaped three-center two-electron (C-C-C)+ bonding array.
The structures and reactivities of the complexes between carbenium ions (R(+)) and acetylene or propyne have been investigated with the aid of electron-correlated quantum mechanical calculations (hybrid density functional, perturbation theory, and coupled cluster methods). Depending on the R group, the acetylene/carbenium ion interaction can produce either an "open" 3c-2e structure or the conventional vinyl cation structure. The "open" 3c-2e C-C-C bonding geometry exists as a minimum for R = methyl and primary/secondary/tertiary alkyl, and hence is the most notable. The alignment of three carbon centers is neither bridged nor linear, but L-shaped, and represents a new type of "open" 3c-2e bonding that has so far escaped proper attention.
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Mechanism of substitution reaction on sp2-carbon center with lithium organocuprate.
Theory and experiments suggest that the substitution reaction of a lithium dialkylcuprate(I) with an alkenyl bromide takes place through a pi-complex (cuprio(III)cyclopropane) that directly breaks down to the alkenylated product rather than via a conventional three-centered transition state. This mechanism is consistent with the broader mechanistic picture of the organocuprate reactions and accounts for the retentive stereochemistry and the kinetic isotope effect observed in the experiments.
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Thermal and palladium-catalyzed [3 + 2] synthesis of cyclopentadienone acetals from cyclopropenone acetals and acetylenes.
[reaction: see text] Substituted cyclopentadienone acetals (CPDAs) were synthesized by a thermal or palladium-catalyzed [3 + 2] cycloaddition reaction of a substituted cyclopropenone acetal to an electron-deficient acetylene. The synthesis afforded di-, tri-, and tetra-substituted CPDAs of considerable structural varieties that undergo Diels-Alder reaction to produce bicyclo[2.2.1]heptenes.
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Alpha-alkylation of ketones by addition of zinc enamides to unactivated olefins.
A zinc enamide generated from the corresponding N-aryl imine undergoes addition to an unactivated olefin, such as ethylene, 1-octene, and isobutylene, to generate an alpha-alkylated gamma-zincioimine intermediate in good to excellent yield. Terminal and gem-disubstituted olefins react with >99% regioselectivity, allowing the C-C bond formation to take place at the more hindered carbon of the double bond. The organozinc intermediate undergoes further C-C bond formation with a carbon electrophile to give, upon hydrolysis of the imine, an alpha-alkylated ketone bearing a variety of functionalized primary, secondary, and tertiary alkyl groups.
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