Half-sandwich η-arene–ruthenium(II) complexes bearing 1-alkyl(benzyl)-imidazo[4,5-f][1,10]-phenanthroline (IP) derivatives: the effect of alkyl chain length of ligands to catalytic activity

The reaction of bromoalkanes (R–Br; (3), R=C_nH_2n+1, n=4 (a), 8 (b), 12 (c),18 (d)) and bromobenzyl derivatives (R′–Br; (4), R′=CH₂C₆H₂(CH₃)₃-2,4,6 (a); CH₂C₆H(CH₃)₄-2,3,5,6 (b); CH₂C₆(CH₃)₅ (c)) with 1H-imidazo[4,5-f][1,10]-phenanthroline (IP)(L₂) gave the corresponding 1-R-imidazo[4,5-f][1,10]-phenanthroline (IPR)(L_3a–d) and 1-R′-imidazo[4,5-f][1,10]-phenanthroline(IPR')(L_4a–c) ligands, respectively. Treatment of L_3a–d and L_4a–d with [Ru(p-cymene)Cl₂]₂ led to the formation of [Ru(p-cymene)(IPR)Cl]Cl (RuL_3a–d) and [Ru(p-cymene)(IPR′)Cl]Cl (RuL_4a–c). New ruthenium(II) complexes RuL_3a–d and RuL_4a–c were characterized by elemental analysis, FTIR, UV–visible and NMR spectroscopy. In order to understand effects of these changes on the N-substituent of imidazol on IP and how they translate to catalytic activity, these new RuL₂, RuL_3a–d and RuL_4a–c were applied in the transfer hydrogenation of ketones by 2-propanol in presence of potassium hydroxide. The activities of the catalysts were monitored by NMR and GC analysis.     

High-pressure NMR study of migratory CO-insertion in palladium-methyl complexes modified with Cs-symmetrical 1,4-diphosphines

Carbonylation of the palladium complexes [PdCH₃(P^∧P′)Cl] (P^∧P′ = 1a, 1b, 1c, 1d, 1e) and [PdCH₃(P^∧P′)(CH₃CN)](OTf) was investigated by means of high-pressure NMR with the determination of the half-life times t_1/2. The results were rationalized on the basis of the electronic properties of the diphosphines and the nature of the solvento ligand in the first coordination sphere. The crystal structures of the complexes [Pd(1b)Cl₂] and [Pd(1b)(H₂O)₂](OTf)₂ are described (1b = 1-(diphenylphosphinomethyl)-2-[bis(3- trifluoromethylphenyl)phosphinomethyl]benzene).     

Efficient synthesis of novel dipyridoimidazoles and pyrido[1′,2′;1,2]imidazo[4,5-d]pyridazine derivatives

Novel dipyrido[1,2-a;3′,4′-d]imidazoles 7a-d, dipyrido[1,2-a;4′,3′-d]imidazoles 8a,c and pyrido[1′,2′;1,2]imidazo[4,5-d]pyridazine derivatives 9a-d were synthesized by two pathways: thermal electrocyclic reaction of 3-alkenylimidazopyridine-2-oximes 10 and direct condensation of ethyl glycinate (or hydrazine) with 2,3-dicarbonylimidazo[1,2-a]pyridines 11.     

Carbonylation studies of Pd-methyl complexes modified with 1,4-Cs-symmetrical diphosphine ligands

Neutral palladium methyl chloride 2a-d [PdCH₃(PˆP′)Cl] and cationic palladium methyl acetonitrile mono-triflate 3a-d [PdCH₃(PˆP′)(CH₃CN)](CF₃SO₃) complexes were synthesized and fully characterized (PˆP′ = 1a-d). All the neutral and cationic complexes containing a C_s-symmetric diphosphine exist in solution as a mixture of geometric isomers. The carbonylation at atmospheric pressure of the neutral and cationic complexes revealed that migratory insertion of carbon monoxide is not stereospecific in these systems. The neutral and cationic acyl complexes were formed in situ as mixtures of stereoisomers, which were characterized by means of NMR spectroscopy.The crystal structures of [Pd(1a)Cl]₂(OTf)₂ and 2d are described.     

Synthesis and properties of novel 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^‡) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03 kcal mol⁻¹ by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄⁻ and 12a-c·BF₄⁻) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄⁻) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄⁻ and 12a,c·BF₄⁻ in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄⁻ and 12a-c·BF₄⁻ observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄⁻ and 12a-c·BF₄⁻ were studied, and structural characterization of 11c·BF₄⁻ based on the X-ray crystal analysis and MO calculation was also performed.     

Intramolecularly coordinated organoantimony(III) carboxylates

The reactions of organoantimony chlorides L^1,2SbCl₂1 and 2 ([2,6-(ROCH₂)₂C₆H₃]⁻, R = Me; L¹ and R = t-Bu; L²) with silver salts of selected carboxylic acids resulted to corresponding organoantimony carboxylates L^1,2Sb(OOCR′)₂, 1a-c (for L¹) and 2a-c (for L²), where R′ = CH₃ for 1a, 2a; R′ = CHCH₂ for 1b, 2b and R′ = CF₃ for 1c, 2c. All compounds were characterized by the help of elemental analysis, ESI-MS, ¹H and ¹³C NMR spectroscopy. The solid state structure investigation using single crystal X-ray diffraction techniques (2a, c) and IR spectroscopy revealed significant differences in coordination mode of both O,C,O chelating ligand and carboxylic groups in this set of compounds. The structure of all compounds in solution of non-coordinating solvent (CDCl₃) was determined by means of variable temperature ¹H, ¹³C, ¹⁹F NMR spectroscopy and IR spectroscopy.     

Thermal and microwave assisted reactions of 2,5-disubstituted thienosultines with [60]fullerene: non-Kekulé biradicals and self-sensitized oxygenation of the cycloadduct

Refluxing an o-dichlorobenzene solution of 2,5-disubstituted thienosultines 10a-f with [60]fullerene for 2-24 h gave both 1:1 and 2:1 cycloadducts in 37-79% isolated yields. The reaction was highly accelerated by microwave irradiation giving comparable yields of cycloadducts. Sultines 10a-f underwent cheletropic extrusion of SO₂ to form the corresponding non-Kekulé biradical intermediates 11a-f, which were subsequently trapped by [60]fullerene to form corresponding cycloadducts. The activation energy barriers (ΔG_c^≠) determined for the boat-to-boat inversion of these 4′,5′,6′,7′-tetrahydrobenzo[c]thieno-[5′,6′:1,2][60]fullerene adducts 12a-f were found to be in the range of 13.5-14.8 kcal/mol. Unexpectedly, one of the monoadduct 12a was found to be labile when kept in air under ambient light. Two new products 15 (a sulfine-enone) and 16 (an endione) were isolated from the decomposed 12a and were found to derive from self-sensitized singlet oxygen reaction on the 2,5-dimethylthieno moiety of 12a.     

The cyclopalladation reaction of 2-phenylaniline revisited

2-Phenylaniline reacted with Pd(OAc)₂ in toluene at room temperature for 24 h in a one-to-one molar ratio and with the system PdCl₂, NaCl and NaOAc in a 1 (2-phenylaniline):1 (PdCl₂):2 (NaCl):1 (NaOAc) molar ratio in methanol at room temperature for one week to give the dinuclear cyclopalladated compounds (μ-X)₂[Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}]₂ [1a (X = OAc) and 1b (X = Cl)] in high yield. Moreover, the reaction between 2-phenylaniline and Pd(OAc)₂ in one-to-one molar ratio in acid acetic at 60 °C for 4 h, followed by a metathesis reaction with LiBr, allowed isolation of the dinuclear cyclopalladated compound (μ-Br)₂[Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}]₂ (1c) in moderate yield. A parallel treatment, but using monodeuterated acetic acid (DOAc) as solvent in the cyclopalladation reaction, allowed isolation of a mixture of compounds 1c, 1c_d1 [Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄](μ-Br)₂[Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)-3-d-C₆H₃] and 1c_d2 (μ-Br)₂[Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)-3-d-C₆H₃}]₂ in moderate yield and with a deuterium content of ca. 60%. 1a and 1b reacted with pyridine and PPh₃ affording the mononuclear cyclopalladated compounds [Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}(X)(L)] [2a (X = OAc, L = py), 2b (X = Cl, L = py), 3a (X = OAc, L = PPh₃) and 3b (X = Cl, L = PPh₃)] in a yield from moderate to high. Furthermore, 1a reacted with Na(acac) · H₂O to give the mononuclear cyclopalladated compound 4 [Pd{κ²-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}(acac)] in moderate yield. ¹H NMR studies in CDCl₃ solution of 2a, 2b, 3a, 3b and 4 showed that 2a and 3a presented an intramolecular hydrogen bond between the acetato ligand and the amino group, and were involved in a dynamic equilibrium with water present in the CDCl₃ solvent; and that the enantiomeric molecules of 2b and 4 were in a fast exchange at room temperature, while they were in a slow exchange for 2a, 3a and 3b. The X-ray crystal structures of 3b and 4 were determined. 3b crystallized in the triclinic space group with a = 9.9170(10), b = 10.4750(10), c = 12.0890(10) Å, α = 98.610(10)°, β = 94.034(10)° and γ = 99.000(10)° and 4 in the monoclinic space group P2₁/a with a = 11.5900(10), b = 11.2730(10), c = 12.2150(10) Å, α = 90°, β = 107.6560(10)° and γ = 90°.     

Nitrile ligands activation in dinuclear aminocarbyne complexes

The diiron complexes [Fe(Cp)(CO){μ-η²:η²-C[N(Me)(R)]NC(C₆H₃R′)CCH(Tol)}Fe(Cp)(CO)] (R = Xyl, R′ = H, 3a; R = Xyl, R′ = Br, 3b; R = Xyl, R′ = OMe, 3c; R = Xyl, R′ = CO₂Me, 3d; R = Xyl, R′ = CF₃, 3e; R = Me, R′ = H, 3f; R = Me, R′ = CF₃, 3g) are obtained in good yields from the reaction of [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(p-NCC₆H₄R′)(Cp)₂]⁺ (R = Xyl, R′ = H, 2a; R = Xyl, R′ = Br, 2b; R = Xyl, R′ = OMe, 2c; R = Xyl, R′ = CO₂Me, 2d; R = Xyl, R′ = CF₃, 2e; R = Me, R′ = H, 2f; R = Me, R′ = CF₃, 2g) with TolCCLi. The formation of 3 involves addition of the acetylide at the coordinated nitrile and C-N coupling with the bridging aminocarbyne together with orthometallation of the p-substituted aromatic ring and breaking of the Fe-Fe bond. Complexes 3a-e which contain the N(Me)(Xyl) group exist in solution as mixtures of the E-trans and Z-trans isomers, whereas the compounds 3f,g, which posses an exocyclic NMe₂ group, exist only in the Z-cis form. The crystal structures of Z-trans-3b, E-trans-3c, Z-trans-3e and Z-cis-3g have been determined by X-ray diffraction experiments.     

Synthesis and reactivity of asymmetrically substituted ansa-bridged zirconocene complexes: X-ray crystal structures of [Zr{R(H)C(η-C5Me4)(η-C5H4)}Cl2] (R = Bu, Bu) and [Zr{Bu(H)C(η-C5Me4)(η-C5H4)}(CH2Ph)2]

The dialkyl complexes, (R = Prⁱ, R′ = Me (2a), CH₂Ph (3a); R = Buⁿ, R′ = Me (2b), CH₂Ph (3b); R = Bu^t, R′ = Me (2c), CH₂Ph (3c); R = Ph, R′ = Me (2d), CH₂Ph (3d)), have been synthesized by the reaction of the ansa-metallocene dichloride complex, [Zr{R(H)C(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] (R = Prⁱ (1a), Buⁿ (1b), Bu^t (1c), Ph (1d)), and two molar equivalents of the alkyl Gringard reagent. The insertion reaction of the isocyanide reagent, CNC₆H₃Me₂-2,6, into the zirconium-carbon σ-bond of 2 gave the corresponding η²-iminoacyl derivatives, [Zr{R(H)C(η⁵-C₅Me₄)(η⁵-C₅H₄)}{η²-MeCNC₆H₃Me₂-2,6}Me] (R = Prⁱ (4a), Buⁿ (4b), Bu^t (4c), Ph (4d)). The molecular structures of 1b, 1c and 3b have been determined by single-crystal X-ray diffraction studies.     

Rhodium(I) carbonyl complexes of tetradentate chalcogen functionalized phosphines, [P(X)(CH2CH2P(X)Ph2)3] {X = O, S, Se}: Synthesis, reactivity and catalytic carbonylation reaction

The reaction of [Rh(CO)₂Cl]₂ with 0.5 mol equivalent of the ligands [P^′(X)(CH₂-CH₂P(X)Ph₂)₃](P^′P₃X₄) {where X = O(a), S(b) and Se(c)} affords tetranuclear complexes of the type [Rh₄(CO)₈Cl₄(P^′P₃X₄)] (1a-1c). The complexes 1a-1c have been characterized by elemental analyses, mass spectrometry, IR and multinuclear NMR spectroscopy, and the ligands b and c are structurally determined by single crystal X-ray diffraction. 1a-1c undergo oxidative addition (OA) reactions with CH₃I to generate Rh(III) oxidised products. Kinetic data for the reaction of 1a and 1b with excess CH₃I indicate a pseudo first order reaction. The catalytic activity of 1a-1c for the carbonylation of methanol to acetic acid and its ester show a higher Turn Over Frequency (TOF = 1349-1748 h⁻¹) compared to the well-known species [Rh(CO)₂I₂]⁻ (TOF = 1000 h⁻¹) under the similar experimental conditions. However, 1b and 1c exhibit lower TOF than 1a, which may be due to the desulfurization and deselinization of the ligands in the respective complexes under the reaction conditions.     

Trifluoroacetylacetonate rhodium(III) methyl complexes, cis-[Rh(TFA)(PPh3)2(CH3)(L)][BPh4] and cis-[Rh(TFA)(PPh3)2(CH3)(I)] (L = CH3CN, NH3, pyridine), in comparison with their acetylacetonate analogs

The oxidative addition of CH₃I to planar rhodium(I) complex [Rh(TFA)(PPh₃)₂] in acetonitrile (TFA is trifluoroacetylacetonate) leads to the formation of cationic, cis-[Rh(TFA)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (1), or neutral, cis-[Rh(TFA)(PPh₃)₂(CH₃)(I)] (4), rhodium(III) methyl complexes depending on the reaction conditions. 1 reacts readily with NH₃ and pyridine to form cationic complexes, cis-[Rh(TFA)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (2) and cis-[Rh(TFA)(PPh₃)₂(CH₃)(Py)][BPh₄] (3), respectively. Acetylacetonate methyl complex of rhodium(III), cis-[Rh(Acac)(PPh₃)₂(CH₃)(I)] (5), was obtained by the action of NaI on cis-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] in acetone at −15 °C. Complexes 1-5 were characterized by elemental analysis, ³¹P{¹H}, ¹H and ¹⁹F NMR. For complexes 2, 3, 4 conductivity data in acetone solutions are reported. The crystal structures of 2 and 3 were determined. NMR parameters of 1-5 and related complexes are discussed from the viewpoint of their isomerism.     

Liquid crystal behaviour of ionic allylpalladium complexes containing 2-pyrazolylpyridine as bidentate N,N′-ligand

Two types of Pd-complexes containing the new N,N′-ligands 2-[3-(4-alkyloxyphenyl)pyrazol-1-yl]pyridine (pz^Rpy; R = C₆H₄OC_nH_2n+1, n = 6 (hp), 10 (dp), 12 (ddp), 14 (tdp), 16 (hdp), 18 (odp)) (1-6), namely c-[Pd(Cl)₂(pz^Rpy)] (7-10) and c-[Pd(η³-C₃H₅)(pz^Rpy)]BF₄ (11-16), have been synthesised and characterised by different spectroscopic techniques. Those members of the second type containing the largest chains (R = ddp 13, tdp 14, hdp 15, odp 16) have been found to have liquid crystal properties showing smectic A mesophases. By contrast, neither the free ligands pz^Rpy nor their related c-[Pd(Cl)₂(pz^Rpy)] complexes exhibited mesomorphism. The new synthesised metallomesogens are mononuclear complexes with an unsymmetrical molecular shape as deduced from the X-ray structures of c-[Pd(η³-C₃H₅)(pz^Rpy)]BF₄ (R = hp, 11; dp, 12). Both compounds, which are isostructural, show a distorted square-planar environment on the palladium centres defined by the allyl and the bidentate pz^Rpy ligands. The crystal structure reveals that both the counteranion and the pz^Rpy ligand function as a source of hydrogen-bonding and intermolecular π?π contacts resulting in a ²D supramolecular assembly.     

Recoverable cationic Pd-catalyzed Heck reaction under thermomorphic mode

The reaction of allylpalladium chloride dimer and 4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy, 1a-c, in the presence of AgOT_f resulted in the synthesis of cationic complex, [Pd(η³-allyl)(4,4′-bis-(R_fCH₂OCH₂)-2,2′-bpy)](OT_f), 2a-c where R_f = C₉F₁₉ (a), C₁₀F₂₁ (b), C₁₁F₂₃ (c), respectively. The solubility curves of 2a-c which began from virtually zero below −40 °C and increased dramatically at slightly higher temperature were quantitatively measured. Upon changing from −40-90 °C there was several orders of magnitude increase of solubility for 2a-c. The cationic Pd-catalyzed Heck arylation of methyl acrylate was selected to demonstrate the feasibility of recycling usage with 2b,c as the catalyst using DMF as the solvent at 140 °C for 3 h in each run. At the end of each cycle, the product mixtures were cooled to −30 °C, and then catalysts were recovered by decantation. The products were quantified by GC analysis or by the isolated yield. The Heck reaction of C₆H₅I with methyl acrylate could be catalyzed by 2b with good recycling results for a total of 15 times and also with a 100% selectivity favoring the trans product. To our knowledge, this is the first example of cationic Pd-catalyzed Heck reaction under the thermomorphic mode.     

Steric and electronic effects in stabilizing allyl-palladium complexes of “P-N-P” ligands, X2PN(Me)PX2 (X = OC6H5 or OC6H3Me2-2,6)

The chemistry of η³-allyl palladium complexes of the diphosphazane ligands, X₂PN(Me)PX₂ [X = OC₆H₅ (1) or OC₆H₃Me₂-2,6 (2)] has been investigated.The reactions of the phenoxy derivative, (PhO)₂PN(Me)P(OPh)₂ with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = H or Me; R′ = H, R″ = Me) give exclusively the palladium dimer, [Pd₂{μ-(PhO)₂PN(Me)P(OPh)₂}₂Cl₂] (3); however, the analogous reaction with [Pd(η³-1,3-R′,R″-C₃H₃)(μ-Cl)]₂ (R′ = R″ = Ph) gives the palladium dimer and the allyl palladium complex [Pd(η³-1,3-R′,R″-C₃H₃)(1)](PF₆) (R′ = R″ = Ph) (4). On the other hand, the 2,6-dimethylphenoxy substituted derivative 2 reacts with (allyl) palladium chloro dimers to give stable allyl palladium complexes, [Pd(η³-1,3-R′,R″-C₃H₃)(2)](PF₆) [R′ = R″ = H (5), Me (7) or Ph (8); R′ = H, R″ = Me (6)].Detailed NMR studies reveal that the complexes 6 and 7 exist as a mixture of isomers in solution; the relatively less favourable isomer, anti-[Pd(η³-1-Me-C₃H₄)(2)](PF₆) (6b) and syn/anti-[Pd(η³-1,3-Me₂-C₃H₃)(2)](PF₆) (7b) are present to the extent of 25% and 40%, respectively. This result can be explained on the basis of the steric congestion around the donor phosphorus atoms in 2. The structures of four complexes (4, 5, 7a and 8) have been determined by X-ray crystallography; only one isomer is observed in the solid state in each case.     

New bis(fluoro-ponytailed) bipyridine ligands for Pd-catalyzed Heck reactions under fluorous biphasic catalysis condition

Three highly fluorinated bipyridine derivatives (4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy) {R_f=HCF₂(CF₂)₇ (1a), n-C₈F₁₇ (1b), n-C₁₀F₂₁ (1c)} have been synthesized using 4,4′-bis(BrCH₂)-2,2′-bpy and the corresponding fluorinated alkoxides. The fluorine contents of ligands 1a-c are 58.3, 59.8, and 62.3%, respectively. Despite its high fluorine content, the ligand 1a with a -CF₂H polar terminal group is more soluble in organic solvents. The ligand 1b is a white solid and is still moderately soluble in CH₂Cl₂. The ligand 1c has a high fluorophilicity, the partition ratio being 42:1 for the n-C₈F₁₈/CH₂Cl₂ system. The reaction of ligands 1a-c with [PdCl₂(CH₃CN)₂] results in the novel Pd complexes [PdCl₂(4,4′-bis-(R_fCH₂OCH₂)-2,2′-bpy)] where R_f=HCF₂(CF₂)₇ (2a), n-C₈F₁₇ (2b), n-C₁₀F₂₁ (2c), respectively. The Pd complex 2b is a pale yellow solid, and has been tested unsatisfactorily for FBC. Insoluble in organic solvents, the Pd complex 2c dissolves only in fluorinated solvents, for instance FC77, which is mainly n-C₈F₁₈. The novel Pd complex 2c has been tested as a catalyst in Heck reactions under a fluorous biphasic catalysis condition. It was found that the Pd complex 2c, after an easy separation, keeps its catalytic activity (>90% yield), even after seven runs. The TGA studies indicate that the Pd complexes 2a-c are stable up to 330 °C.     

Titanium mediated alkylidenation of substituted cycloalkenones: scope and limitations

The conversion of the cyclopent-2-enone 5 and cyclohex-2-enones 11a, c-e into corresponding α′-exo-alkylidene compounds using Ti(IV) catalysis, with PPh₃ and an aldehyde, is described.     

Total synthesis of apigenin 7,4′-di-O-β-glucopyranoside, a component of blue flower pigment of Salvia patens, and seven chiral analogues

We have succeeded in the first total synthesis of apigenin 7,4′-di-O-β-d-glucopyranoside (1a), a component of blue pigment, protodelphin, from naringenin (2). Glycosylation of 2 according to Koenigs-Knorr reaction provided a monoglucoside 4a in 80% yield, and this was followed by DDQ oxidation to give apigenin 7-O-glucoside (12a). Further glycosylation of 4′-OH of 12a with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl fluoride (5a) was achieved using a Lewis acid-and-base promotion system (BF₃·Et₂O, 2,6-di-tert-butyl-4-methylpyridine, and 1,1,3,3-tetramethylguanidine) in 70% yield, and subsequent deprotection produced 1a. Synthesis of three other chiral isomers of 1a, with replacement of d-glucose at 7 and/or 4′-OH by l-glucose (1b-d), and four chiral isomers of apigenin 7-O-β-glucosides (6a,b) and 4′-O-β-glucosides (7a,b) also proved possible.     

Regio- and stereoselective cycloadditions of (1Z,4R,5R)-1-arylmethylidene-4-benzoylamino-3-oxo-5-phenylpyrazolidin-1-ium-2-ides to methyl methacrylate

[3+2] Cycloadditions of (1Z,4R^∗,5R^∗)-1-arylmethylidene-4-benzoylamino-3-oxo-5-phenylpyrazolidin-1-ium-2-ides 1a-e to methyl methacrylate gave the 1-CO₂Me regioisomers 3/3′, exclusively, in 1-67% yields. Stereocontrol was dependent on the ortho-substituents at the 1′-aryl group in dipole 1: ortho-unsubstituted dipoles 1a-c gave the major (1R^∗,3R^∗,5R^∗,6R^∗)-isomers 3a-c, whilst ortho-disubstituted dipoles gave the major (1R^∗,3S^∗,5R^∗,6R^∗)-isomers 3′d,e. The structures of cycloadducts were determined by NMR and X-ray diffraction.     

Asymmetric Friedel-Crafts alkylation of activated benzenes with methyl (E)-2-oxo-4-aryl-3-butenoates catalyzed by [Pybox/Sc(OTf)3]

The asymmetric Friedel-Crafts reaction between methyl (E)-2-oxo-4-aryl-3-butenoates (1a-c) and activated benzenes (2a-d) has been efficiently catalyzed by the Sc^III triflate complex of (4′S,5′S)-2,6-bis[4′-(triisopropylsilyl) oxymethyl-5′-phenyl-1′,3′-oxazolin-2′-yl]pyridine (pybox 3). The 4,4-diaryl-2-oxo-butyric acid methyl esters (4) are usually formed in good yields and the enantioselectivity is up to 99% ee. The sense of the stereoinduction can be rationalized with the same octahedral complex (10) between 1, pybox 3 and Sc triflate already proposed for other reactions involving pyruvates, and catalyzed by the same complex.