Nickel(II) chloride hexahydrate catalyzed reaction of aromatic aldehydes with 2-mercaptoethanol: formation of supramolecular helical assemblage of the product

Various aromatic aldehydes on reaction with 2-mercaptoethanol provided an unanticipated product, bis(2-hydroxyethyl)dithioacetals (3) as the major product along with the expected product 1,3-oxathiolanes (4) in the presence of 0.05 equiv amount of nickel(II) chloride hexahydrate (NiCl₂·6H₂O) under solvent-free conditions. Products 3c and 3e exhibit an interesting hydrogen-bonded infinite supra-molecular helical structure.     

Regioselective Baeyer-Villiger lactonization of 2-substituted pyrrolidin-4-one. Synthesis of statine

Nine 2-substituted pyrrolidin-4-ones 4a-i were obtained via a series of functional group transformation of known prolinol 5 by facile six kinds of methodologies. The target structure of 1,3-amino alcohols 2a-i was constructed in the regioselective Baeyer-Villiger lactonization of ketones 4a-i and reduction of the resulting 4-substituted tetrahydro-1,3-oxazin-6-ones 3a-i. A new and straightforward synthesis of (3S,4S)-statine (6) has been established starting from trans-(2S,4R)-4-hydroxyproline (1).     

On the microstructure and symmetry of apparently hexagonal BaAl2O4

The P6₃ (a=2a_p, b=2b_p, c=c_p) crystal structure reported for BaAl₂O₄ at room temperature has been carefully re-investigated by a combined transmission electron microscopy and neutron powder diffraction study. It is shown that the poor fit of this P6₃ (a=2a_p, b=2b_p, c=c_p) structure model for BaAl₂O₄ to neutron powder diffraction data is primarily due to the failure to take into account coherent scattering between different domains related by enantiomorphic twinning of the P6₃22 parent sub-structure. Fast Fourier transformation of [0 0 1] lattice images from small localized real space regions (∼10 nm in diameter) are used to show that the P6₃ (a=2a_p, b=2b_p, c=c_p) crystal structure reported for BaAl₂O₄ is not correct on the local scale. The correct local symmetry of the very small nano-domains is most likely orthorhombic or monoclinic.     

Palladium complexes of N-aryl-2-pyridylamines

Palladium complexes of N-phenyl-2-pyridylamine (4) and dipyridylamine substrates (7, 11) have been studied. Due to the coordination ability of the pyridine-nitrogen atoms, the pyridyl substrates, 4, 7, 11 were subjected to Pd(OAc)₂ complexations and a number of N-aryl-2-pyridylamine Pd complexes (13-17) were isolated and characterised, in particular by NMR and ESI-MS. A new method for the preparation of the acetato-bridged six-membered ring palladacycle complex (13) of 4 is reported. The dipyridyl amines 7, 11 formed cis/trans bis-dentate acetato-bridged dimeric Pd₂Lig₂(OAc)₂ (14a,b/16a,b) and Pd₃Lig₂(OAc)₄ complexes (15a,b/17a,b). The N-aryl-2-pyridylamine substrates (4, 7, 11) were prepared by oxidative nucleophilic substitution, by 1,3-cycloaddition reaction or by Buchwald amination.     

(Fluorosilyl)ethylenediamines and fluorosilyl-1,3-diaza-2-silacyclopentanes

This paper presents the chemistry of ethylenediamines and fluorosilanes. The synthesis of thermally stable monosilyl (1-5)- and bis(fluorosilyl)ethylenediamines (6) is described. Starting with the dilithium salt of ethylenediamine and F₂Si(CMe₃)₂ the five-membered 1,3-diaza-2-silacyclopentane (8) is obtained. The reaction of tetra- and trifluorosilanes with dilithiated bis(silyl)ethylenediamines leads to the formation of 1,3-diaza-2-fluorosilylsilacyclopentanes (9-14). Fluorosilanes substitute 8 in 1 and 3 positions (15-28). A fluorosilyl-bridged five-membered ring (29) is isolated in the reaction of 1-trimethylsilyl-1,3-diaza-2-silacyclopentane, BuLi and MeSiF₃. In the synthesis of N-fluorosilyl-1,3-diaza-2-silacyclopentanes constitutional isomers were formed (30-33). Quantum-chemical calculations support the isomerisation mechanism. An iminosilane with an SiN double bond is the intermediate product of the rearrangement process.Crystal structures of 7, 13, 20 and 23 are reported.     

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.     

Highly enantioselective copper-catalyzed conjugate addition of diethylzinc to cyclic enones with spirocyclic phosphoramidite ligands

A series of spirocyclic phosphoramidite ligands 6-9 with different substituents on the amine moiety were synthesized from the chiral spirocyclic diol (R)-5. These monodentate ligands have been applied in copper-catalyzed conjugate addition of diethylzinc to cyclic enones. Excellent enantioselectivities (up to 99% ee) can be achieved by the use of ligand (R,S,S)-9 bearing stereochemically matched structure derived from the C₂-symmetric (S,S)-bis(α-methylbenzyl)amine.     

Supramolecular nanostructured assemblies of different types of porphyrins with fullerene using TiO2 nanoparticles for light energy conversion

TiO₂ nanoparticles were modified with porphyrin derivatives, 5-[4-benzoic acid]-10,15,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (Ar-H₂P-COOH), 5-[4-benzoic acid]-10,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (H-H₂P-COOH), and 5,10,15,20-tetra[4-benzoic acid]-21H,23H-porphyrin (H₂P-4COOH). The porphyrin-modified TiO₂ nanoparticles were deposited on nanostructured OTE/SnO₂ electrode together with nanoclusters of fullerene (C₆₀) in acetonitrile-toluene (3/1, v/v) using an electrophoretic deposition technique to afford the porphyrin-modified TiO₂ composite electrode denoted as OTE/SnO₂/(porphyrin-modified TiO₂ nanoparticle+C₆₀)_n. The porphyrin-modified TiO₂ composite electrodes have efficient light absorbing properties in the visible region, exhibiting the photoactive response under visible light excitation using redox couple. The incident photon-to-photocurrent efficiency (IPCE) values of supramolecular nanostructured electrodes of porphyrin-modified TiO₂ nanoparticles with fullerene [OTE/SnO₂/(Ar-H₂P-COO-TiO₂+C₆₀)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂+C₆₀)_n] are much larger than those of the reference systems of porphyrin-modified TiO₂ nanoparticles without C₆₀ [OTE/SnO₂/(Ar-H₂P-COO-TiO₂)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂)_n]. In particular, the maximum IPCE value (41%) is obtained for OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n under the bias potential of 0.2 V versus SCE. This indicates that the formation of supramolecular complexes between porphyrins and fullerene on TiO₂ nanoparticles plays an important role in improvement of the light energy conversion properties.     

Reactions of P4S10 and pyPS2Cl with N,N′-diphenylurea and N,N′-diphenylthiourea

The reaction of P₄S₁₀ (1) with N,N′-diphenylurea (PhNH)₂CO (2) results in new heterocyclic compounds: the pyridinium salt of 1,3-diphenyl-2-sulfido-2-thioxo-1,3-diaza-2λ⁵-phosphetidine (3) (with a P–N–C–N cycle) and the pyridinium salt of 1,4-diphenyl-2,5-disulfido-2,5-dithioxo-1,4-dithiadiaza-2λ⁵,5λ⁵-diphosphinane (4), containing the (P–S–N)₂ cycle and the cyclic thiophosphates [pyH]₂[P₂S₈] (5), [pyH]₂[P₂S₇] (6) and [pyH]₃[P₃S₉] (7). A similar reaction, but carried out with N,N′-diphenylthiourea (PhNH)₂CS (8), leads to the formation of 4 and 6. pyPS₂Cl (9), used as an alternative starting material, also yields compounds 3, 4, 5, and further [pyH][PS₂Cl₂] (10) and S₈ after reaction with 2. Compound 3 reacts with Pd(CH₃COO)₂, with the formation of the complex [Pd(Ph₂N₂COPS₂)₂] (11). The crystal structures of 3 and 7 were determined by single-crystal X-ray diffraction.     

Microwave-assisted synthesis of novel bis(2-thioxothiazolidin-4-one) derivatives as potential GSK-3 inhibitors

(5Z,5′Z)-3,3′-(1,4-Phenylenebis(methylene)-bis-(5-arylidene-2-thioxothiazolidin-4-one) derivatives (5a-r) have been synthesized by the condensation reaction of 3,3′-(1,4- or 1,3-phenylenebis(methylene))bis(2-thioxothiazolidin-4-ones) (3a,b) with suitably substituted aldehydes (4a-f) or 2-(1H-indol-3-yl)2-oxoacetaldehydes (8a-c) under microwave conditions. The bis(2-thioxothiazolidin-4-ones) were prepared from the corresponding primary alkyl amines (1a,b) and di-(carboxymethyl)-trithiocarbonyl (2). The 2-(1H-indol-3-yl)-2-oxoacetaldehydes (8a-c) were synthesized from the corresponding acid chlorides (7a-c) using HSnBu₃.     

Kinetics and mechanistic studies of the interaction of thiosulfate with cis-diaqua-bis[1-alkyl-2-(arylazo)imidazole]ruthenium(II) complexes

The nucleophilic substitution reaction of S₂O₃²⁻ with [Ru(HaaiR′)₂(OH₂)₂](ClO₄)₂ (1) [HaaiR′ = 1-alkyl-2-(phenylazo)imidazole] and [Ru(ClaaiR′)₂(OH₂)₂](ClO₄)₂ (2) [ClaaiR′ = 1-alkyl-2-(chlorophenylazo)imidazole] [where R′ = Me(a), Et(b) or Bz(c)] in acetonitrile–water (50% v/v) medium to yield Na₂[Ru(HaaiR′)₂(S₂O₃)₂] (3a, 3b or 3c) and Na₂[Ru(ClaaiR′)₂(S₂O₃)₂] (4a, 4b or 4c) has been studied. The products were characterized by microanalytical data and spectroscopic techniques (UV–Vis, NMR and mass spectroscopy). The reaction proceeds in two consecutive steps (A → B → C); each step follows first order kinetics with respect to each complex and S₂O₃²⁻, and the first step second order rate constant (k′₂) is greater than the second step one (k″₂). An increase in the π-acidity of the ligand increases the rate. Thermodynamic parameters, the standard enthalpy of activation (Δ^‡H⁰) and the standard entropy of activation (Δ^‡S⁰), have been calculated for both steps using the Eyring equation from variable temperature kinetic studies. The low Δ^‡H⁰ and large negative Δ^‡S⁰ values indicate an associative mode of activation for both aqua ligand substitution processes.     

Synthesis and structural characterization of enantiopure exo and endo six-membered oxazoline-derived palladacycles

Direct palladation of (S)-4-benzyl-2-methyl-2-oxazoline (1) and (S)-2-benzyl-4-tert-butyl-2-oxazoline (2) using Pd(OAc)₂ in MeCN afforded the corresponding μ-acetato-dimeric complexes with six-membered exo and endo palladacycles, respectively. The same complexes were obtained by reacting coordination complexes Pd(1)₂(OAc)₂ and Pd(2)₂(OAc)₂ with Pd(OAc)₂ in MeCN. Metalation of (S)-2,4-dibenzyl-2-oxazoline (3) with Pd(OAc)₂ in AcOH, MeCN or CH₂Cl₂ resulted in the regiospecific formation of the six-membered endo palladacycle. The obtained μ-acetato-dimeric complexes were converted to the corresponding μ-chloro-dimeric derivatives 7, 11 and 13 by treatment with LiCl in acetone. The mononuclear PPh₃ adducts 8, 12 and 14 were obtained by reacting dimers 7, 11 and 13 with PPh₃ in benzene. NMR spectroscopy data supported the proposed structures of all complexes and suggested that exo and endo palladacycles in 8 and 12 have rigid boat conformations in CHCl₃. The X-ray crystal structures of the μ-acetato dimer 6 with the exo palladacycle and the PPh₃ adduct 14 with the endo metalacycle revealed boat conformation of both palladacycles and chiral twisted conformations δ(S) and λ(S), respectively, of the oxazoline rings in the solid state.     

Ring opening of chiral 2-(1-aminoalkyl)epoxides by aliphatic thiols with total selectivity: synthesis of enantiopure 3-amino-1-(alkylthio)alkan-2-ols

We have studied the thiolysis of (2R,1′S)- or (2S,1′S)-2-(1-aminoalkyl)epoxides 1 or 2 in the presence of BF₃·OEt₂. The ring opening took place at C-3 with complete regioselectivity, affording the corresponding enantiopure (2R,3S)- or (2S,3S)-3-amino-1-(alkylthio)alkan-2-ols 3 or 4 in good or high yield. The structures of compounds 3 and 4 have been proposed based on HMBC NMR experiments.     

Salen-ligands based on a planar-chiral hydroxyferrocene moiety: Synthesis, coordination chemistry and use in asymmetric silylcyanation

Condensation of the O-protected hydroxyferrocene carbaldehyde (S_p)-1 with suitable diamines, followed by liberation of the hydroxyferrocene moiety leads to a new type of ferrocene-based salen ligands (3). While the use of ethylenediamine in the condensation reaction yields the planar-chiral ethylene-bridged ligand [(S_p,S_p)-3a], reaction with the enantiomers of trans-1,2-cyclohexylendiamine gives rise to the corresponding diastereomeric cyclohexylene-bridged systems [(S,S,S_p,S_p)-3b and (R,R,S_p,S_p)-3c], which feature a combination of a planar-chiral ferrocene unit with a centrochiral diamine backbone. Starting with the ferrocene-aldehyde derivative (R_p)-1, the enantiomeric ligand series (3d/e/f) is accessible via the same synthetic route.The (S_p)-series of these newly developed N₂O₂-type ligands was used for the construction of the corresponding mononuclear bis(isopropoxy)titanium (4a/b/c), methylaluminum (5a/b/c) and chloroaluminum-complexes (6a/b/c), which were isolated in good yields and identified by X-ray diffraction in several cases. The aluminum complexes (5/6) were successfully used in the Lewis-acid catalyzed addition of trimethylsilylcyanide to benzaldehyde, yielding the corresponding cyanohydrins in 45-62% enantiomeric excess.     

Synthesis and structural revision of eurypamides isolated from the Palauan sponge Microciona eurypa

Eurypamides A and B, 1 and 2, were successfully synthesized by employing Tl(NO₃)₃ (TTN) oxidation of the corresponding halogenated phenols, 9, 16, and 26. This investigation revealed that the dihydroxyarginine residue of 1 should be revised to possess (2S,3R,4S)-configuration. In addition, the synthesis of 2 provided a pure sample, which was previously characterized in a mixture.     

Group 12 metal coordination polymers of 1,2-bis(diphenylphosphino)ethane dioxide: A persistent 1D chain motif and consequent 2D and 3D architectures

A series of group 12 metal coordination polymers with 1,2-bis(diphenylphosphino)ethane dioxide (dppeO₂), {[ZnCl₂(μ-dppeO₂)]·CH₂Cl₂}_n (1·CH₂Cl₂), [ZnBr₂(μ-dppeO₂)]_n (2), [CdI₂(μ-dppeO₂)]_n (4), [(HgI₂)₂(μ-dppeO₂)]_n (5), [Zn(SCN)(μ-SCN)(μ-dppeO₂)]_n (6), and [Cd(NO₃)(μ-SCN)(μ-dppeO₂)]_n (7), have been synthesized and structurally characterized. The structures of the compounds are all based on an infinite 1D chain constructed by four-coordinate metal ions and dppeO₂ ligands adopting the trans bridging coordination fashion. In the coordination polymers 1, 2 and 4, the halide ions act as terminal ligands, leading to discrete 1D chains with alternative MX₂ and dppeO₂ repeating units. The mercury compound 5 features a unique square-wave-like inorganic chain –[Hg(1)–I–Hg(2)–I]–, and the 1D HgI₂(μ-dppeO₂) chains are further linked by HgI₂ bridges to form a 3D network. In the thiocyanate-containing compounds 6 and 7, the 1D chains are linked by one (6) or two (7) bridging SCN^– ions to result in 2D layered structures. Solid-state emission spectra of the coordination polymers show different variations compared to the free dppeO₂ ligand, such as enhancement (1, 2, 6 and 7), shift (3 and 4) and quenching (5) upon metal coordination.     

Synthesis, properties and complexation of (pS)-1-isocyano-2-methylferrocene, the first planar-chiral isocyanide ligand

Reaction of enantiomerically pure, planar-chiral (_pS)-1-bromo-2-methylferrocene (1) with phthalimide in the presence of Cu₂O produces (_pS)-1-phthalimido-2-methylferrocene (2), quantitative reduction of which with hydrazine hydrate affords (_pS)-1-amino-2-methylferrocene (3) with >99% ee. Formylation of amine 3 followed by dehydration of the resulting (_pS)-1-formamido-2-methylferrocene (4) provides (_pS)-1-isocyano-2-methylferrocene (5), the first example of a planar-chiral isocyanide ligand, in a good yield. Isocyanide 5 reacts with PdI₂ to give the crystallographically characterized chiral complex trans-[PdI₂{(_pS)-1-isocyano-2-methylferrocene}₂] (6). The redox behavior of 4, 5, and 6, accessed by cyclic voltammetry, is discussed.     

Cyclopalladation of enantiopure oxazolines having the prochiral CMe2 moiety at position 2 of the heterocycle

(R)-4-Ethyl-2-(1,1-dimethylpropyl)-2-oxazoline (1) and (S)-4-tert-butyl-2-(1,1-dimethylbutyl)-2-oxazoline (2) were synthesized in two steps from the corresponding enantiopure amino alcohols and acid chlorides in a total yield of 95% and 72%, respectively. (S)-2-(1-Adamantyl-1-methylethyl)-4-isobutyl-2-oxazoline (3) was obtained from adamantyl bromide and l-leucinol in five steps in a total yield of 82%. Reactions of oxazolines 1–3 with Pd(OAc)₂ in AcOH or CH₂Cl₂ followed by treatment with LiCl afforded the corresponding μ-Cl dimeric cyclopalladated complexes 15, 17, and 20 in good yield. Compounds 15, 17, and 20 reacted with PPh₃ to furnish the corresponding mononuclear complexes 16, 19, and 21. The ³¹P NMR spectra of trans(N,P) adducts 16, 19, and 21 contained signals of two diastereomers in a ratio of ca. 1.3:1.     

Autoxidation of isotachysterol

Isotachysterol, the acid-catalyzed isomerization product of vitamin D₃, produces seven previously unknown oxygenation products in a self-initiated autoxidation reaction under atmospheric oxygen in the dark at ambient temperature. They are (5R)-5,10-epoxy-9,10-secocholesta-6,8(14)-dien-3β-ol (6a), (5S)-5,10-epoxy-9,10-secocholesta-6,8(14)-dien-3β-ol (6b), (10R)-9,10-secocholesta-5,7,14-trien-3β,10-diol (7a), (10S)-9,10-secocholesta-5,7,14-trien-3β,10-diol (7b), (7R,10R)-7,10-epoxy-9,10-secocholesta-5,8(14)-dien-3β-ol (8), 5,10-epidioxyisotachysterol (9) and 3,10-epoxy-5-oxo-5,10-seco-9,10-secocholesta-6,8(14)-dien-10-ol (10). The formation of these products is explained in terms of free radical peroxidation chemistry.     

Optically active cyclopentadienyl and indenyl ligands obtained from lactic acid esters

Asymmetric cyclopentadienes and indenes are easily prepared by nucleophilic attack of LiCp or LiInd on tosylate or triflate of ethyl (S)-(−) lactate. The selectivity of the reaction depends on the nature of the leaving group. This is particularly true in the case of the reaction of LiCp with sulfonates of ethyl (S)-(−) lactate. Indeed, only the monosubstituted cyclopentadiene lactate 2 is obtained from the triflate 6, whereas from the tosylate 1, besides 2 (20%) a 1,3-disubstituted cyclopentadiene lactate 3 is isolated (16.5%). From cyclopentadiene and indene lactate 2 and 7, optically active β-hydroxycyclopentadiene 10 and β-hydroxyindene 11 are obtained by reduction with LiAlH₄. Two rhodium(I) complexes 14 and 15 have been synthesized from (R,S)-2-(cyclopentadienyl)N,N-dimethylpropanamide 12 and (S)-2-(cyclopentadiene)propan-1-ol 10, respectively. The molecular structure of these complexes has been determined. Analytical and preparative chiral HPLC have been used to determine the optical purity of the ligands and to isolate enantiopure cyclopentadienyl complexes from racemic or enantiomerically enriched rhodium(I) complexes.