Mechanistic study of the aldol condensation occurring in the alkaline solution of 3-hydroxy 2-oxo propranoate (β hydroxypyruvate)

With 3-bromo-2-oxopropanoate (β bromopyruvate) and its ethyl ester, the ionisation of the gemdiol of the hydrated form BrCH₂-C(OH)₂-COOR 1 initiates the elimination of bromide anion yielding 3-hydroxy-2-oxopropanoate 2 (β-hydroxypyruvate). The mechanism of the reaction was investigated essentially by polarography in aqueous solution.In neutral (and acid) media, the polarographic behaviour of 2 resembled that of other α-ketoacids: reduction at the mercury electrode yielded glycerate.In alkaline media, there was evidence of the carbanion enolate ^-O—CHC(OH)—COO^-. 3'. The overall rate constant was determined according to a kinetic law of the typer:v = k.¦2¦.¦OH^-¦; found k = 1,56 min^-1 in NaOH 0.5 N at 25°.In the pH range 10.5 to 11.5,3' existed in minor amounts and initiated a slow aldol condensation with the tautomer 3-oxo-2-hydroxypropanoate 4 (tartronate Semialdehyde) according to a kinetic law of the type v = k?.¦2¦².¦OH^-¦found k? = 211.mol^-1 min ^-1 at 25° , at pH 11.0.The aldol product was isolated as a sodium sail and its structure established by ¹³C NMR.     

Highly diastereoselective alkylation,acylation and aldol condensation of cis- and trans-(N-acyloyl)hexahydrobenzoxazolidin-2-ones

The potential of hexahydrobenzoxazolidinones 1a–d as chiral auxiliaries was explored. N-Acylation of 1a–d, 2a–d and 3a–d was followed by methylation and benzylation via the corresponding sodium enolates generated by treatment with NaHMDS. Diastereoselectivities of 98% or higher were observed. The absolute configuration of the newly created stereogenic center was established by chemical correlation with 2-benzyl-1-propanol. The stereochemical results are congruent with addition to the electrophile from the less hindered face of a (Z)-configured enolate, the sodium cation being coordinated by both carbonyl oxygens of the substrate. cis- and trans-N-Propionyl derivatives 2a–d were treated with Bu₂BOTf/Et₃N to give dialkylboron enolates 6a–d, which were then reacted with acetaldehyde and benzaldehyde. ¹H and ¹³C NMR analyses showed the formation of a single diastereomeric aldol addition product, whose relative configuration was ascertained as syn from the measurement of the ³J_{H(2′)/H(3′)} coupling constants, and whose absolute configuration was determined by X-ray crystallographic analysis. The results are rationalized in terms of a Zimmerman–Traxler transition state, with a (Z)-configured enolate where boron is coordinated to the aldehyde carbonyl rather than the oxazolidinone carbonyl. Substrate 2a was also reacted with acyl chlorides via the sodium enolate (NaHMDS). The effect of reaction conditions on O- versus C-acylation, as well as the influence of solvent and additives on diastereoselectivity, are discussed.     

Synthesis and properties of titanium glycolate Ti(OCH2CH2O)2

A new efficient method for the synthesis of extended micro-and nano-sized crystals (whiskers, fibers) of titanium glycolate Ti(OCH₂CH₂O)₂ has been suggested. The method implies the reaction of hydrated titanium dioxide with ethylene glycol on heating in air. Thermolysis of Ti(OCH₂CH₂O)₂ in air gives titanium dioxide as anatase (400–500°C) and rutile (T > 700°C), the morphology of titanium glycolate crystals being inherited by the oxide. The pseudocrystals of the thermolysis product in an inert gas medium (T = 500–950°C) represent aglomeration of nano-sized titanium dioxide particles and amorphous carbon. At temperatures up to 1300°C, the formation of the TiO_2?x C _x phase with a rutile structure is probable. In a wet air environment, titanium glycolate is partially hydrolyzed to give TiO _x (OCH₂CH₂O)_2?2x (OH)_2x ·xH₂O (0 ≤ x ≤ 1) and on keeping in water at room temperature, ethylene glycol is completely displaced from the crystals. This process is also not accompanied by changes in the particle morphology.     

Chelating diamide complexes of titanium: new catalyst precursors for the highly active and living polymerization of α-olefins

The reaction of RHN(CH₂)₃NHR (1a,b) (a, R=2,6-ⁱPr₂C₆H₃; b, R=2,6-Me₂C₆H₃) with 2 equiv of BuLi followed by 2 equiv of ClSiMe₃ yields the silylated diamines R(Me₃Si)N(CH₂)₃N(SiMe₃)R (3a,b). The reaction of 3a,b with TiCl₄ yields the dichloride complexes [RN(CH₂)₃NR]TiCl₂ (4a,b) and two equiv of ClSiMe₃. An X-ray study of 4a (P2₁/n, a=9.771(1) Å, b=14.189(1) Å, c=21.081(2) Å, β=96.27(1)°, V=2905.2(5) ų, Z=4, T=25°C, R=0.0701, R_w=0.1495) revealed a distorted tetrahedral geometry about titanium with the aryl groups lying perpendicular to the TiN₂-plane. Compounds 4a,b react with 2 equiv of MeMgBr to give the dimethyl derivatives [RN(CH₂)₃NR]TiMe₂ (5a,b). An X-ray study of 5b (P2₁2₁2₁, a=8.0955(10) Å, b=15.288(4) Å, c=16.909(3) Å, V=2092.8(7) ų, Z=4, T=23°C, R=0.0759, R_w=0.1458) again revealed a distorted tetrahedral geometry about titanium with titanium–methyl bond lengths of 2.100(9) Å and 2.077(9) Å. These titanium dimethyl complexes are active catalysts for the polymerization of 1-hexene, when activated with methylaluminoxane (MAO). Activities up to 350,000 g of poly(1-hexene)/mmol catalyst·h were obtained in neat 1-hexene. These systems actively engage in chain transfer to aluminum. Equimolar amounts of 5a or 5b and B(C₆F₅)₃ catalyze the living aspecific polymerization 1-hexene. Polydispersities (M_w/M_n) as low as 1.05 were measured. Highly active living systems are obtained when 5a is activated with {Ph₃C}⁺[B(C₆F₅)₄]⁻. A primary insertion mode (1,2 insertion) has been assigned based on both the initiation of the polymer chain and its purposeful termination with iodine.     

Synthesis of the first water-soluble C2-symmetric bis(oxazolidinone) as a potential bifunctional chiral auxiliary

The first water-soluble C₂-symmetric bis(oxazolidinone) 1, a potential bifunctional chiral auxiliary, has been synthesized via regioselective intramolecular cyclization of a biscarbamate. The sodium enolate derived from N,N′-di(phenylacetyl)bis(oxazolidinone) 7 reacts with methyl iodide with high facial selectivity (95:5).     

The stereoselective addition of titanium(IV) enolates of 1,3-oxazolidin-2-one and 1,3-thiazolidine-2-thione to cyclic N-acyliminium ion. The total synthesis of (+)-isoretronecanol

(+)-Isoretronecanol (1) has been prepared in four steps and 36% overall yield via the diastereoselective addition of the titanium(IV) enolate derived from N-4-chlorobutyryl-1,3-thiazolidine-2-thione (3) to N-Boc-2-methoxypyrrolidine (5), which afforded 2-substituted pyrrolidine 7 in 84% yield (8:1 diastereoisomeric ratio), followed by reductive recovery of the chiral auxiliary and cyclization.     

Electrical conductivities of bis(1,3-dithiole-2-thione-4,5-dithiolato)rhodate anion salts

RhCl₃·3H₂O reacted with Na₂dmit (dmit²⁻; 1,3-dithiole-2-thione-4,5-dithiolate anion) and [NBu₄ⁿOH in methanol to afford [NBu₄ⁿ][Rh(dmit)₂] (1) and [NBu₄ⁿ]_1.5[Rh(dmit)₂] (2). Salt 1 was oxidized electrochemically in acetonitrile to afford [NBu₄ⁿ]_0.4[Rh(dmit)₂] (3). Suspended powders of 1 or 2 reacted with iodine in hexane to afford [NBu₄ⁿ][Rh(dmit)₂][I₃]_1.3 (4) or [NBu₄ⁿ]_1.5[Rh(dmit)₂[I₃]_0.4 (5). On the other hand, 1 dissolved in acetonitrile, reacted with bromine and iodine to yield [NBu₄ⁿ]_0.25[Rh(dmit)₂Br] (6) and [NBu₄ⁿ]_0.35[Rh(dmit)₂I] (7), respectively. All the salts behave as semi-conductors with electrical conductivities of 1 x (10⁻⁵ − 10⁻⁸) S cm⁻¹ at 25°C measured for compacted pellets. Electronic absorption, ESR and X-ray photoelectron spectra of the salts are discussed.     

Free energies of aqueous mixtures of NaH2PO4 and NAClO4: Evidence for the species (H2PO4) 2 −2

The system NaH₂PO₄?NaClO₄ has been studied from 0.15 to 7.0 mole-kg^?1 at 25°C by the isopiestic method. The excess free energy of mixing is large and positive. The results confirm the formation of (H₂PO₄) ₂ ^?2 dimers with a stoichiometric association constantK _a=0.25±0.1 kg-mole^?1 at 25°C.     

Organo-directed synthesis of a 3-D open-framework mixed-metal oxide, [enH2][Mn3(V2O7)2(H2O)2], incorporating metal trimer building blocks

Synthesis of [enH₂][Mn₃(V₂O₇)₂(H₂O)₂] 1, the first of a new class of organically derivatized mixed metal oxides, is achieved at pH 8 and 140°C by hydrothermal reaction of [Mn₃O(OAc)₆(py)₃][BF₄], V₂O₅, NH₂CH₂CH₂NH₂ (en) and H₃BO₃ in a 0.67: 1: 6: 10 ratio. Crystals of 1 are triclinic P-1, a=5.743(1) Å, b=7.931(1) Å, c=9.313(1) Å, α=68.54(1), β=85.78(1), γ=84.50(1)°, V=392.62(9) ų. The X-ray structure refined to R=0.025. Compound 1 has an anionic open 3-D framework based on linear tri-manganese units of edge shared [Mn^(II)O₆] octahedra connected through divanadate [V₂O₇] groups. The organic counterions are located in 1-D tunnels generated from six-membered [Mn₂V₄] rings. The temperature dependent magnetic susceptibility of 1 indicates a paramagnetic to anti-ferromagnetic transition with a Néel temperature of 10 K.     

Reaction of MeO2C(H)C=C=C(H)CO2Me with Ru3(CO)12. New diruthenium complexes with bridging carboxylate-substituted allene ligands

The reaction of Ru₃(CO)₁₂ with MeO₂C(H)C=C=C(H)CO₂ Me has yielded two isomeric productsanti-Ru₂(CO)₆[μ-η ³-η ¹-MeO₂C(H)CCC(H)CO₂Me],1 in 70% yield andsyn-Ru₂(CO)₆[μ-η ³-η ¹-MeO₂C(H)CCC(H)CO₂Me],2 in 5% yield. Both compounds were characterized by single crystal X-ray diffraction analysis. Both products are diruthenium complexes with bridging di(carboxylate)allene ligands in which the oxygen atom of the carbonyl group of one of the carboxylate groupings is coordinated to one of the metal atoms. Compound1 isomerizes partially to2 at 68°C. Crystal Data for1: space group=P2₁/n,a=11.131(1) Å,b=10.228(2) Å,c=15.978(2) Å,β=102.01(1)°,Z=4, 1653 reflections,R=0.025; for2: space group=P $\bar 1$ ,a=9.340(1) Å,b=14.925(4) Å,c=6.778(2) Å,α=99-02(2)°,β=104 62(2)°,γ=94.58(2)°,Z=2, 1857 reflections,R=0.027.     

A Thermochemical Study on the Formation of Oxalato-Titanium(III) Complex

The thermometric titration of titanium(III) chloride with oxalic acid was carried out at 25°C. The molar ratio of titanium (III): oxalate was found to be 1:2, which indicates the formation of Ti(C₂O₄)₂⁻ ion in acid media. The limiting value of the heat of reaction between Ti(III) ion and oxalic acid in hydrochloric acid solution was found to be −1.5 Kcal mole⁻¹ at 25°C.     

Synthesis,characterisation and structural aspects of a new diorganotin(IV) complex with <Emphasis Type="Italic">N</Emphasis>′-(5-bromo-2-hydroxybenzylidene)benzoylhydrazone ligand

A new diorganotin(IV) complex, Me₂Sn[5-Br-(2-OC₆H₄CH=N–N=C(O)Ph)] (1) has been synthesised from dimethyltin(IV) dichloride and a Schiff base derived from 5-bromosalicylaldehyde and benzoyl hydrazide. The complex has been characterised by elemental analysis, and FT-IR and NMR spectroscopies. Molecular structure has been confirmed by single-crystal X-ray diffraction analysis. Complex 1 crystallises in triclinic system, space group P-1 (no. 2) with a=7.562(6), b=9.980(8), c=11.899(8) Å; α=81.08(6)°, β=72.71(5)°, γ=79.64(6)°; Z=2. The ligand N′-(5-bromo-2-hydroxybenzylidene)benzoylhydrazone (H₂L) coordinates to the metal centre in enolate form via the phenolic O, imino N and enolic O atoms. The central tin atom is in distorted trigonal bipyramidal geometry with two oxygen atoms of the ligand in axial positions, while the imino nitrogen atom of the ligand and two methyl groups on tin occupy the equatorial sites.     

Temperature-dependent racemic compound-conglomerate crystallization of 2,3:6,7-dibenzobicyclo[3.3.1]nona-2,6-diene-4,8-dione

2,3:6,7-dibenzobicyclo[3.3.1]nona-2,6-diene-4,8-dione 1 is a new example of a compound capable of temperature-dependent racemate-conglomerate crystallization: at temperatures below 90°C crystals of the racemic compound (space group P1̄, Z=4) can be obtained, whereas above 100°C a conglomerate of (+)- and (−)-homochiral crystals (space group P2₁2₁2₁, Z=4) forms and therefore it undergoes spontaneous resolution upon crystallization. Enantioselective analytical gas chromatography on a single crystal has been proposed as a simple method for detection of conglomerate formation. The ¹H and ¹³C NMR spectra of 1 are analyzed in detail and the crystal structures of both species (racemic compound and single enantiomer) have been solved by X-ray structural analysis.     

Synthesis of 2-phenyl-1,3-di(4-pyridyl)naphthvalene by photoinduced reversible valence isomerization of 2-phenyl-1,3-di(4-pyridyl)naphthalene

2-Phenyl-1,3-di(4-pyridyl)naphthvalene 3a was synthesized by the photoinduced reversible valence isomerization of 2-phenyl-1,3-di(4-pyridyl)naphthalene 2a. Then, 3a was converted into 3-phenyl-1,2-di(4-pyridyl)naphthalene 4a and 2a simultaneously. The t_1/2 of 3a in DMSO-d₆ at 90 °C was 2 h, while that at 110 °C was approximately 10 min.     

Monomeric five-coordinate rhenium diazenido and hydrazido complexes with aromatic thiolate ligands: X-ray structures of [Re(NNC6H4-Br)2(SC6H3-2,5-Me2)(PPh3)2] and [ReO(NNMePh)(SPh)3], and of the synthetic precursor [Re(NNC6H4-4-Br)2Cl(PPh3)2]

Reaction of [ReOCl₃(PPh₃)₂] with bromophenylhydrazine in methanol yields [ReCl(N₂C₆H₄Br)₂(PPh₃)₂] (1). Complex 1 reacts with arylthiolates to give mixtures of [Re(SAr)(N₂C₆H₄Br)₂(PPh₃)₂] (2) and [Re₂(SAr)₇(NNR)₂]⁻. Complexes 1 and 2 display trigonal bipyramidal geometries with the phosphine ligands occupying the axial sites. A significant feature of the structures is the nonequivalence of the rhenium-diazenido moieties, such that for 1 the ReN(1) and N(1)N(2) distances are 1.80(2) and 1.24(3) Å, while ReN(3) and N(3)N(4) are 1.73(2) and 1.32(3) Å, and for 2 the ReN distances are 1.73(1) and 1.80(2)° with corresponding NN distances of 1.32(2) and 1.25(2) Å. Reaction of (PPh₄)[ReO(SPh)₄] (3) with unsymmetrically disubstituted hydrazines affords complexes of the type [ReO(SPh)₃(NMRR′)] (R = Me, R′ = Ph for 4). Complexes 3 and 4 display distorted square pyramidal geometries with the oxo groups apical. The significant feature of the structure of 4 is the nonlinear ReN(1)N(2) linkage, exhibiting an angle of 145.6(10)°. The angle does not appear to correlate with a significant contribution from a valence form with sp² hybridization at the α-nitrogen. Crystal data: 1: monoclinic space group, P2₁/n, a = 12.216(2) Å, b = 19.098(2) Å, c = 20.257(4) Å, β = 106.20(1)°, V = 4538.3(8) ų to give Z = 4; structure solution and refinement based on 1905 reflections converged at R = 0.070. 2: monoclinic space group P2₁/n, a = 14.393(2) Å, b = 18.842(3) Å, c = 20.717(4)Å, β = 110.26(1)°, V = 5270.5(8) ų to give Z = 4 for D = 1.53 g cm⁻¹; structure solution and refinement based on 4249 reflections to give R = 0.070. 3: monoclinic space group P2₁/n, a = 12.531(2) Å, b = 24.577(4) Å, c = 16.922(3) Å, β = 99.06(1)°, V = 5146.2(9) ų, D = 1.36 g cm⁻³ for Z = 4, 2912 reflections, R = 0.050. 4: monoclinic space group p2₁/n, a = 16.137(2) Å, b = 9.863(2) Å, c = 16.668(2) Å, β = 111.12(1)°, V = 2474.7(6) ų, D = 1.74 g cm⁻³ for Z = 4, 2940 reflections, R = 0.066.     

Preparation and structural characterization of Os(II) and Ru(II) complexes,MCl2(vdpp)2 [M = Os or Ru,vdpp = 1,1-bis(diphenylphosphino)ethene]

A reaction between Os₂(O₂CCH₃)₄Cl₂ and vdpp [vdpp = 1,1-bis(diphenylphosphino) ethene] was investigated. When the reactants, in the presence of LiCl, were heated in toluene OsCl₂(vdpp)₂,1, was formed. In a similar reaction Ru₂(O₂CCH₃)₄Cl with vdpp afforded RuCl₂(vdpp)₂,2. The molecular structures of1 and2 were elucidated using X-ray crystallography. Single crystals of1 and2 grown from dichloromethanehexane crystallize in the space group P2₁/c with these cell dimensions: a = 11.046(2)Å, b = 18.168(3)Å, c = 12.678(3)Å, β = 110.24(2)° and V = 2387(2)ų for1 and a = 11.055(1)Å, b = 18.199(3)Å, c = 12.693(2)Å, β = 110.16(1)°, V = 2392(1)ų for2. The molecules of1 and2 are isostructural. Metal atoms reside on inversion centers relating the two halves of the molecules. The complexes are six-coordinate with two four-membered chelate rings and trans chlorine atoms. For RuCl₂(vdpp)₂ the PMP angle in the chelate ring is 73.13(2)° and the PCP angle in the chelate ring is 98.6(1)°. These values are 72.74(3)° and 97.9(2)°, respectively, for OsCl₂(vdpp)₂. There is a disordered dichloromethane solvent molecule present in the lattice and there are no unusual intermolecular contacts.     

Synthesis and structure of triphenylantimony diphthalate

Triphenylantimony diphthalate hydrate (I) has been synthesized by the reaction between triphenylantimony and ortho-phthalic acid in the presence of hydrogen peroxide (molar ratio, 1: 2: 1). According to X-ray diffraction data, the antimony atom in a symmetric molecule of compound I (the SbC₃O₂ coordinating moiety has point group C _2v ) has a trigonal bipyramidal coordination. The OSbO axial angle and the CSbC angles in the equatorial plane are 179.83(12)° and 106.04(9)°, 147.93(18)°, respectively. The bond length are 2.153(2) (Sb-O), and 2.110(4), 2.120(3) Å (Sb-C). Intramolecular Sb…O=C contacts (2.802(3) Å) take place in compound I.     

The synthesis and crystal structure of 5-acetyl-2'-deoxyuridine

5- Acetyl - 2' - deoxyuridine (1) has been synthesised by treating 2' - deoxy - 5 - ethynyluridine with dilute sulphuric acid. Condensation of the trimethylsilyl derivative of 5-acetyluracil with 2-deox-3, 5-di-O-p-toluoyl-α-d-erythropen chloride gave a mixture of α- and β-anomeric blocked nucleosides from which the α-anomer was isolated and the p-toluoyl groups removed to give 5 - acetyl -1 - (α - d - 2- deoxyerythropentofuranosyl) uracil. Only a poor yield of the β-anomer (1) was obtained by this procedure. The UV spectra and m.p. obtained for 1 differed from the values quoted in the literature. The crystals of 1 are monoclinic, space group P2₁, with a = 9.525, b = 12.16, c = 5.22 Å, β = 92.03° and two molecules in the unit cell. The structure was refined by least-squares calculations to R 3.4% for 1426 observed counter amplitudes. The pyrimidine ring is essentially planar with the acetyl group inclined at 6° to it. The sugar ring has the highly unusual C(4')-exo conformation and the arrangement about C(4')-C(5') is such that O(5') is oriented gauche with respect to both O(1') and C(3'). The glycosidic torsion angle O(1')-C(1')-N(1)-C(6) is 56° (anti conformation).     

Carbon-nitrogen bond formation in the reaction of the reaction of diphenyl diazomethane Ph2 CN2 with diiron-carbene complexes (Fe2(CO)7x03BD;-C(R)C(NEt2)x03BD;-C(R)C(NEtx03BC;-C(R)C(NEt2)N(NCPh2)x03BC;-C(R)C(NEtx03BC;-C(R)C(NEt2)NN(CPh2)x03BC;-C(R)C(NEt)]

The diiron ynamine complex [Fe₂(CO)₇{μ-CR)C(NEt₂)}] (1:R=Me,2:R = C₃H₅.3:R=SiMe₃.4:R = Ph) reacts at room temperature with diphenyldiazomethane Ph₂CN₂, in hexane to yield complexes [Fe₂(CO)₆{C(R)C(NEt₂)N (NCPh₂)] (5a:R=Me,6a:R=C₃H₅.7a R=SiMe₃.8a:R=Ph) resulting from the insertion of the terminal nitrogen atom into the Fe=C carbene bond. Insertion the second nitrogen atom and formation of compounds [Fe₂(CO)₆zμ-C(R)C(NEt₂)NN(CPh₂)}] (5b:R=Me,6b:R=C₃H₅,7b:R=SiMe₃,8b:R=Ph) is observed when compounds5a-5a are treated in refluxing hexane. Transformation of compoundsa tob is also obtained at room temperature within a few days. All compounds were identified by their¹H NMR spectra. Compounds6a, 7a, 8a, and8b were characterized by single crystal X-ray diffraction analyses. Crystal data: for6a: space group = P2₁/n,a=12.853(1) A,b=24.800(7) A,c=8.947(6) A,β=99.29(3)°,Z=4, 2227 rellectionsR=0,038; for7a: space group=Pl,a=ll.483(4) A,b=14.975(4) A,c = 17.890(8) A,α = 82.80(3)°,β=94.29(7)°,γ=85.42(2),Z = 4, 5888 reflectionR = 0.035: for8a: space group = Pcab.a = 31.023(8) A.b=20.137(1) A.c=9.686(2) A.Z=8. 1651 reflections,R=0.071; for8b: space group=P2₁/n,a=21.459(4),b=10,100(3) A,c=28,439(8) A,ß=103.86(4)°,Z=8. 2431 reflections.R=0.057.