Intramolecular Nucleophilic Acyl Substitution Reaction of 3,4-Alkadienyl Carbonates Mediated by Ti(O-i-Pr)(4)/2 i-PrMgCl Reagent. Efficient Synthesis of Optically Active beta,gamma-Unsaturated Esters with an alpha-Substituent

Treatment of 3,4-alkadienyl carbonates 2a-i with a low-valent titanium reagent diisopropoxy(eta(2)-propene)titanium (1), readily generated by the reaction of Ti(O-i-Pr)(4) with 2 i-PrMgCl, resulted in an intramolecular nucleophilic acyl substitution (INAS) reaction to afford vinyltitanium compounds 3 which, in turn, reacted with H(3)O(+), D(2)O, or iodine to give alpha-substituted beta,gamma-unsaturated esters 4 in good to excellent yields. The olefin moiety of the hydrolysis product 4 has (Z)-geometry mainly except for 4h. Starting from chiral 2f or 2g, the reaction proceeded stereospecifically to give optically active alpha-substituted beta,gamma-unsaturated ester 4f or 4g having (Z)-olefin geometry exclusively.     

An allyltitanium derived from acrolein 1,2-dicyclohexylethylene acetal and (eta(2)-propene)Ti(O-i-Pr)(2) as a chiral propionaldehyde homoenolate equivalent that reacts with imines with excellent stereoselectivity. An efficient and practical access to optically active gamma-amino carbonyl compounds

A chiral allyltitanium compound 2, prepared in situ by the reaction of optically active acrolein 1,2-dicyclohexylethylene acetal (3) with (eta(2)-propene)Ti(O-i-Pr)(2) (1), reacts with a variety of acyclic and cyclic imines 4 in a regiospecific way to afford alpha-addition products 5 as a mixture of the E- and Z-isomers in good combined yield, where the former is predominant in a ratio of 92:8 to >95:5. The mixture of (E)- and (Z)-5 and pure (E)-5 which could be isolated in several cases were respectively converted to the corresponding beta-amino ester 6 to confirm the absolute configuration and enantiomeric purity. The ee of the newly formed asymmetric center of 5 is more than 78% for the mixture of (E)- and (Z)-5 and more than 96% for pure (E)-5. By taking advantage of the versatility of the vinyl ether moiety in 5, optically active gamma-amino aldehydes 8, gamma-amino aldehyde acetals 7 and 10, gamma-amino acids 9, beta-amino esters 6, and pyrrolidinoisoquinolines 12 were readily prepared. In the reaction of 2 with optically active alpha-silyloxyimine 4n, remarkable double stereodifferentiation was observed; thus, the reaction of 2 derived from (S,S)- or (R,R)-3 provided syn- and anti-5n in a ratio of 55:45 or 0:100, respectively. Meanwhile, the stereochemistry of the product in the reaction of 2 with beta-silyloxyimine 4o was controlled mainly by 2. Thus, the reaction of beta-silyloxyimine 14 with 2 derived from 1 and (R,R)-3 afforded gamma-silyloxyimine 15 with 92% diastereoselectivity, from which 4-amino-6-hydroxypentadecanal dimethyl acetal (13), a key intermediate for the synthesis of batzelladine D, was synthesized.     

Novel addition reactions of titanacycle phosphonates by tuning of Ti(O-i-Pr)4/2i-PrMgCl

Di- or tri-substituted vinylphosphonates, 2-5, can be obtained in a highly regio- and stereoselective manner from 1-alkynylphosphonates, by manipulation of Ti(O-i-Pr)4/2i-PrMgCl.     

Novel rectangular [Fe4(mu4-OHO)(mu-OH)(2)](7+) versus "butterfly" [Fe4(mu3-O2](8+) core topology in the Fe(III)/RCO2(-)/phen reaction systems (R = Me,Ph; phen = 1,10-phenanthroline): preparation and properties of [Fe4(OHO)(OH)(2)(O2CMe)(4)(phen)(4)](ClO4)(3), [Fe4O2(O2CPh)(7)(phen)(2)](ClO4), and [Fe4O2(O2CPh)(8)(phen)(2)

The preparations, X-ray structures, and detailed physical characterizations are presented for three new tetranuclear Fe(III)/RCO(2)(-)/phen complexes, where phen = 1,10-phenanthroline: [Fe(4)(OHO)(OH)(2)(O(2)CMe)(4)(phen)(4)](ClO(4))(3).4.4MeCN.H(2)O (1.4.4MeCN.H(2)O); [Fe(4)O(2)(O(2)CPh)(7)(phen)(2)](ClO(4)).2MeCN (2.2MeCN); [Fe(4)O(2)(O(2)CPh)(8)(phen)(2)].2H(2)O (3.2H(2)O). Complex 1.4.4MeCN.H(2)O crystallizes in space group P2(1)/n, with a = 18.162(9) A, b = 39.016(19) A, c = 13.054(7) A, beta = 104.29(2) degrees, Z = 4, and V = 8963.7 A(3). Complex 2.2MeCN crystallizes in space group P2(1)/n, with a = 18.532(2) A, b = 35.908(3) A, c = 11.591(1) A, beta = 96.42(1) degrees, Z = 4, and V = 7665(1) A(3). Complex 3.2H(2)O crystallizes in space group I2/a, with a = 18.79(1) A, b = 22.80(1) A, c = 20.74(1) A, beta = 113.21(2) degrees, Z = 4, and V = 8166(1) A(3). The cation of 1 contains the novel [Fe(4)(mu(4)-OHO)(mu-OH)(2)](7+) core. The core structure of 2 and 3 consists of a tetranuclear bis(mu(3)-O) cluster disposed in a "butterfly" arrangement. Magnetic susceptibility data were collected on 1-3 in the 2-300 K range. For the rectangular complex 1, fitting the data to the appropriate theoretical chi(M) vs T expression gave J(1) = -75.4 cm(-1), J(2) = -21.4 cm(-1), and g = 2.0(1), where J(1) and J(2) refer to the Fe(III)O(O(2)CMe)(2)Fe(III) and Fe(III)(OH)Fe(III) pairwise exchange interactions, respectively. The S = 0 ground state of 1 was confirmed by 2 K magnetization data. The data for 2 and 3 reveal a diamagnetic ground state with antiferromagnetic exchange interactions among the four high-spin Fe(III) ions. The exchange coupling constant J(bb) ("body-body" interaction) is indeterminate due to prevailing spin frustration, but the "wing-body" antiferromagnetic interaction (J(wb)) was evaluated to be -77.6 and -65.7 cm(-1) for 2 and 3, respectively, using the appropriate spin Hamiltonian approach. M?ssbauer spectra of 1-3 are consistent with high-spin Fe(III) ions. The data indicated asymmetry of the Fe(4) core of 1 at 80 K, which is not detected at room temperature due to thermal motion of the core. The spectra of 2 and 3 analyze as two quadrupole-split doublets which were assigned to the body and wing-tip pairs of metal ions. (1)H NMR spectra are reported for 1-3 with assignment of the main resonances.     

Small gas-phase dianions of Zn3O(4)(2-), Zn4O(5)(2-), CuZn2O(4)(2-), Si2GeO(6)(2-), Ti2O(5)(2-) and Ti3O(7)(2-)

We have searched for new species of small oxygen-containing gas-phase dianions produced in a secondary ion mass spectrometer by Cs+ ion bombardment of solid samples with simultaneous exposure of their surfaces to O2 gas. The targets were a pure zinc metal foil, a copper-contaminated zinc-based coin, two silicon-germanium samples (Si(1-x)Ge(x)(with x= 6.5% or 27%)) and a piece of titanium metal. The novel dianions Zn3O(4)(2-), Zn4O(5)(2-), CuZn2O(4)(2-), Si2GeO(6)(2-), Ti2O(5)(2-) and Ti3O(7)(2-) have been observed at half-integer m/z values in the negative ion mass spectra. The heptamer dianions Zn3O(4)(2-) and Ti2O(5)(2-) have been unambiguously identified by their isotopic abundances. Their flight times through the mass spectrometer are approximately 20 micros and approximately 17 micros, respectively. The geometrical structures of the two heptamer dianions Ti2O(5)(2-), and Zn3O(4)(2-) are investigated using ab initio methods, and the identified isomers are compared to those of the novel Ge2O(5)(2-) and the known Si2O(5)(2-) and Be3O(4)(2-) dianions.     

Investigation of stereoisomers of 4-alkenyl-trans-decahydroquinol-4-ols in mixtures by the method of reaction chromato-mass spectrometry

The mass spectra of the appropriate 4-ethyl derivatives, which provide the determination of the configuration of the 4 position in the initial alcohols, are registered in the chromato-mass spectrometric investigation of mixtures of the stereoisomeric 4-vinyl-trans-decahydroquinol-4-ols using a microreactor for hydrogenation; the microreactor is placed before or after the chromatographic column.Communication 13 of the series Reaction chromato-mass spectrometry. For Communication 12, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1215–1217, September, 1986     

In Situ Study of the Specific Adsorption of HSO(4)(-)/SO(4)(2-) Ions on Hematite by Radiotracer Technique

The specific adsorption of radiolabeled sulfate ions from perchlorate supporting electrolyte on hematite powder has been investigated. It was demonstrated that a measurable adsorption occurs only at pH values under 5. The adsorption capacity of a given amount of hematite powder tends to a limiting value with decreasing pH. A Langmuir-like adsorption isotherm describes the concentration dependence of the adsorption of sulfate species. It was found that the experimental results are in good agreement with the model suggested recently (Hug, S. J. J. Colloid Interface Sci. 188, 415 (1997)). Copyright 2000 Academic Press.     

A novel synthetic method for optically active terpenes by the ring-opening reaction of (R)-(+)-β-methyl-β-propiolactone

Optically active terpene such as (R)-(+)-citronellol, (R)-(+)-pulegone or (S)-ar-turmerone is prepared in high enantiomeric excess from an intermediate, (R)-(+)-citronellic acid or (S)-(+)-3-p-tolylbutyric acid, which is easily prepared by the Sn2 type of ring opening reaction of (R)-(+)-β-methyl-β-propiolactone with homoprenylmagnesium bromide in the presence of a copper(I) salt or di-p-tolylcuprate.     

Selective cleavage of allyl and propargyl ethers to alcohols catalyzed by Ti(O-i-Pr)4/MXn/Mg

[reaction: see text] Allyl and propargyl ethers were effectively deallylated or depropargylated to the parent alcohols via a C-O bond cleavage catalyzed by a low-valent titanium reagent (LVT), Ti(O-i-Pr)4/TMSCl/Mg or Ti(O-i-Pr)4/MgBr2/Mg, under mild reaction conditions. Differentiation between the allyl and propargyl ethers was achieved by the reaction in the presence of AcOEt as an additive. The reagent also catalyzed intra- and intermolecular cyclotrimerization reactions of alkynes to substituted benzenes.     

Preparation of titanated alkoxyallenes from 3-alkoxy-2-propyn-1-yl carbonates and (eta(2)-Propene)Ti(O-i-Pr)(2) as an efficient ester homoaldol equivalent

3-Alkoxy-2-propyn-1-yl carbonates (2) react with a divalent titanium reagent (eta(2)-propene)Ti(O-i-Pr)(2) to afford titanated alkoxyallenes 1 which, in turn, react with aldehydes regiospecifically to provide the corresponding gamma-addition products in good to excellent yields, thus affording a convenient method for synthesizing gamma-hydroxy esters 3 and/or gamma-butyrolactones 4.     

Application of n-Bu4NHF2 as a fluorinating agent for the preparation of fluoroanions: synthesis and crystal structure of the anions [t-BuPO3AlF2]2(2-), [PhPO3AlF2]2(2-), and [(O-i-Pr)3Ti(mu-F)2(mu-O-i-Pr)Ti(O-i-Pr)3]-

The first phosphonate anions of aluminum-containing fluorine and an anionic bridged fluoroalkoxy derivative of titanium have been realized using n-Bu4NHF2 as a fluorinating agent in organometallic synthesis. Reactions of [RPO3AlMe]4 [R = Ph (1), t-Bu] with n-Bu4NHF2 yield organic-soluble compounds of the type [n-Bu4N]2[RPO3AlF2]2 [R = Ph (2), t-Bu (3)], whereas the reaction of Ti(O-i-Pr)4 with n-Bu4NHF2 results in the formation of [n-Bu4N][O-i-Pr)3Ti(mu-F)2(mu-O-i-Pr)Ti(O-i-Pr)3] (4). These compounds have been obtained in high yields and have been adequately characterized through spectroscopic techniques and X-ray diffraction studies.     

The Pd(4)(dppm)(4)(H)(2)(2+) cluster: a precatalyst for the homogeneous hydrogenation of alkynes

The catalytic properties of the title cluster toward the homogeneous hydrogenation of phenylacetylene, diphenylethyne and phenyl-1-propyne have been investigated as a function of temperature, pressure, solvents, substrate and cluster concentrations, and counterions. The title cluster is a precatalyst that exhibits a good catalytic activity under mild conditions (1 atm of H(2) at 20 degrees C) for the hydrogenation of alkynes and alkenes. For the alkyne substrates, the turnover frequencies (tof's) range between 200 and 500 h(-)(1), and the product distribution varies as: cis-products, 75-90%; trans-products; 0-8% after 3 h of reaction. Based on the graphs -d[substrate]/dt vs [Pd(4)](1/2), the mechanism indicates a cluster dissociation into two dimers (presumably of the type Pd(2)(dppm)(2)(H)(solvent)(+)). The variations of tof (or -d[substrate]/dt) as a function of [substrate] and pressure of H(2) are linear. At 1600 psi of H(2), the tof can reach 2500-3000 h(-)(1) (in THF). The tof also increases with temperature reaching a maximum at approximately 35 degrees C (tof: 1000-1300 h(-)(1)), but at higher temperatures cluster decomposition begins to occur, leading to a rapid decrease in rates of catalysis. At 50 degrees C, no catalysis is observed. The hydrogenation reaction can be stopped at the corresponding cis-alkenes with approximately 95% yields, depending on the substrate and experimental conditions used. The tof's also vary with the solvent, where stronger coordinating solvent molecules give higher tof's. In addition, the tof's do not change with the nature of the counterion, which acts as "spectator" in the catalysis.     

Heterobimetallic bismuth-transition metal salicylate complexes as molecular precursors for ferroelectric materials. Synthesis and structure of Bi(2)M(2)(sal)(4)(Hsal)(4)(OR) (4) (M = Nb,Ta; R = CH(2)CH(3), CH(CH(3))(2)), Bi(2)Ti(3)(sal)(8)(Hsal)(2), and Bi(2)Ti(4)(O(i)Pr)(sal)(10)(Hsal) (sal = O(2)CC(6)H(4)-2-O; Hsal = O(2)CC(6)H(4)-2-OH)

The reactions between triphenylbismuth, salicylic acid, and the metal alkoxides M(OCH(2)CH(3))(5) (M = Nb, Ta) or Ti[OCH(CH(3))(2)](4) have been investigated under different reaction conditions and in different stoichiometries. Six novel heterobimetallic bismuth alkoxy-carboxylate complexes have been synthesized in good yield as crystalline solids. These include Bi(2)M(2)(sal)(4)(Hsal)(4)(OR)(4) (M = Nb, Ta; R = CH(2)CH(3), CH(CH(3))(2)), Bi(2)Ti(3)(sal)(8)(Hsal)(2), and Bi(2)Ti(4)(O(i)Pr)(sal)(10)(Hsal) (sal = O(2)CC(6)H(4)-2-O; Hsal = O(2)CC(6)H(4)-2-OH). The complexes have been characterized spectroscopically and by single-crystal X-ray diffraction. Compounds of the group V transition metals contain metal ratios appropriate for precursors of ferroelectric materials. The molecules exhibit excellent solubility in common organic solvents and good stability against unwanted hydrolysis. The nature of the thermal decomposition of the complexes has been explored by thermogravimetric analysis and powder X-ray diffraction. We have shown that the complexes are converted to the corresponding oxide by heating in an oxygen atmosphere at 500 degrees C. The mass loss of the complexes, as indicated by thermogravimetric analysis, and the resulting unit cell parameters of the oxides are consistent with the formation of the desired heterobimetallic oxide. The complexes decomposed to form the bismuth-rich phases Bi(4)Ti(3)O(12) and Bi(5)Nb(3)O(15) as well as the expected oxides BiMO(4) (M = Nb, Ta) and Bi(2)Ti(4)O(11).     

Optical resolution by preferential crystallization of (RS)-2-benzoylamino-2-benzyl-3-hydroxypropanoic acid and its use in synthesizing optically active 2-amino-2-methyl-3-phenylpropanoic acid

To synthesize optically active 2-amino-2-methyl-3-phenylpropanoic acid (1), (RS)-2-benzoylamino-2-benzyl-3-hydroxypropanoic acid [(RS)-2] was first optically resolved using cinchonidine as a resolving agent to yield optically pure (S)- and (R)-2 in yields of about 70%, based on half of the starting amount of (RS)-2. Next, the racemic structure of (RS)-2 was examined based on melting point, solubility, IR spectrum, and binary and ternary phase diagrams, with the aim of optical resolution by preferential crystallization of (RS)-2. Results indicated that the (RS)-2 exists as a conglomerate at room temperature, although it forms a racemic compound at the melting point. The optical resolution by preferential crystallization yielded (S)- and (R)-2 with optical purities of about 90%, which were fully purified by recrystallization. After O-tosylation of (S)- and (R)-2, reduction by zinc powder and sodium iodide gave (R)- and (S)-1, respectively.     

Chemical and Electrochemical Asymmetric Dihydroxylation of Olefins in I(2)-K(2)CO(3)-K(2)OsO(2)(OH)(4) and I(2)-K(3)PO(4)/K(2)HPO(4)-K(2)OsO(2)(OH)(4) Systems with Sharpless' Ligand

Iodine-assisted chemical and electrochemical asymmetric dihydroxylation of various olefins in I(2)-K(2)CO(3)-K(2)OsO(2)(OH)(4) and I(2)-K(3)PO(4)/K(2)HPO(4)-K(2)OsO(2)(OH)(4) systems with Sharpless' ligand provided the optically active glycols in excellent isolated yields and high enantiomeric excesses. Iodine (I(2)) was used stoichiometrically for the chemical dihydroxylation, and good results were obtained with nonconjugated olefins in contrast to the case of potassium ferricyanide as a co-oxidant. The potentiality of I(2) as a co-oxidant under stoichiometric conditions has been proven to be effective as an oxidizing mediator in electrolysis systems. Iodine-assisted asymmetric electro-dihydroxylation of olefins in either a t-BuOH/H(2)O(1/1)-K(2)CO(3)/(DHQD)(2)PHAL-(Pt) or t-BuOH/H(2)O(1/1)-K(3)PO(4)/K(2)HPO(4)/(DHQD)(2)PHAL-(Pt) system in the presence of potassium osmate in an undivided cell was investigated in detail. Irrespective of the substitution pattern, all the olefins afforded the diols in high yields and excellent enantiomeric excesses. A plausible mechanism is discussed on the basis of cyclic voltammograms as well as experimental observations.     

Mechanistic study of alcohol oxidation by the Pd(OAc)(2)/O(2)/DMSO catalyst system and implications for the development of improved aerobic oxidation catalysts

The Pd(OAc)2/O2/DMSO catalyst system displays impressive versatility in the aerobic oxidation of organic substrates, ranging from alcohols to olefins. This report details mechanistic insights into these reactions. Dimethyl sulfoxide (DMSO) plays no redox role in the chemistry, and kinetic experiments identify the turnover-limiting step as DMSO-promoted oxidation of palladium(0) by molecular oxygen. The "chemical oxidase" pathway characterized for this catalyst system holds great promise for the design of new aerobic oxidation reactions.     

K3PO4-KOH Mixture as Efficient Reagent for the Deprotection of 4-Aryl-2-methyl-3-butyn-2-ols to Terminal Acetylenes

A mixture of potassium hydroxide and potassium phosphate was found to be an active reagent mixture for the cleavage of 2-hydroxypropyl-protected acetylenes. The reaction was performed in toluene at reflux temperature and gave terminal acetylenes in good to excellent yields within very short periods of time. Numerous other functional groups are tolerated.

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