Reaction of 3-methoxy-2-methylphenol with 2-ethoxyvinylphosphonic dichloride

Condensation of 2-ethoxyvinylphosphonic dichloride with 3-methoxy-2-methylphenol in dioxane in the presence of trifluoroacetic acid results in 5,13-dimethoxy-4,14-dimethyl-1-phospha-2,16-dioxatetracyclo[7.7.1.0^3,8.0^10,15]heptadeca-3,5,7,10,12,14-hexaene 1-oxide and 2-hydroxy-7-methoxy-8-methyl-2-oxobenzo[e]-1,2-oxophosphorine.     

Base-promoted rearrangement of cage α-haloketones—II : 12-oxa-3,5,9,10-tetrachlorohexacyclo[5.4.1.02,6.03,10.05,9.08,11]-dodecane-4-one

A synthesis of 12-oxa-3,5,9,10-tetrachlorohexacyclo[5.4.1.0^2,6.0^3,10.0^5,9.0^8,11]dodecane-4-one (6) from 4,4-dimethoxy-2,3,5,6-tetrachloropentacyclo [[5.4.0.0^2,6.0^3,10.0^5,9]undecane-8,11-dione (1) is described. Reaction of 6 with sodium hydroxide in refluxing benzene, toluene, or tetrahydrofuran affords 11-oxa-3,4,5-exo-6-tetrachloropentacyclo [[6.2.1.0^2,7.0^4,10.0^5,9]undecane-endo-3-carboxylic acid (7a, 80·2% yield). The corresponding reaction of 6 with refluxing aqueous sodium hydroxide solution affords 4,12-dioxa-8,11-dichlorohexacyclo-[5.4.1.0^2,6.0^3,10.0^5,9.0^8,11]dodecane-1-carboxylic acid (8a, 66·5% yield). A mechanism which accounts for the formation of 7a and 8a from 6 is presented.     

Chemistry of strained polycyclic compounds—V : The stereospecific cationic cage expansion reaction of 4-homocubane carbinols to 1,3-bishomocubane bridgehead alcohols

The cationic rearrangement of four homocubane bridgehead carbinols viz dimethyl 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonyl-9-one ethylene ketal) carbinol 2, diphenyl 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonyl-9-one ethylene ketal) carbinol 3, 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7] nonyl-9-one ethylene ketal) carbinol 4 and 4-(1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonyl) carbinol 16, has been studied undervarious conditions.Exclusive migration of the C₄C₇ (or the equivalent C₃C₄ bond) in the homocubane skeleton was observed leading to 1,3-bishomocubane bridgehead alcohols. Relief of cage constraint governs the selective course of these cage expansions.     

Synthesis of 3,11-Dioxatetracyclo[6.3.0.02,6.05,9]undecanes and 3,5,7-Trioxapentacyclo[7.2.1.02,8.04,11.06,10]dodecane

The synthesis of 3,11-dioxatetracyclo[6.3.0.0^2,6.0^5,9]undecanes has been accomplished from furans in a short sequence by iodine-induced cyclization reaction. The application of iodine-induced cyclization reaction for the synthesis of 3,5,7-trioxapentacyclo[7.2.1.0^2,8.0^4,11.0^6,10]dodecane itself was also demonstrated.     

Computational analysis of the nucleophilic eliminative ring fission of bridgehead substituted 1,3-bishomocubyl acetates

Molecular mechanics (MM2) calculations on the conceivable seco-cage structures by homoketonization of two types of bridgehead substituted 1,3-bishomocubyl acetates, viz. type A : 4-acetoxy-pentacyclo[5.3.0.0^2,5.0^3,9.0^4,8] decan-6-one and its ethylene ketal, and type B: 8-acetoxypentacyclo [5.3.0.0^2,5.0^3,9.0^4,8]decan-6-one, its ethylene ketal and 8-acetoxypentacyclo[5.3.0.0^2,5.0^3,9.0^4,8]decane were performed.     

Evaluation of lipase from Candida rugosa in the resolution of endo-(±)-1,8,9,10,11,11-hexachloropentacyclo[6.2.1.13,6.02,7.05,9]dodecan-4-alcohol

endo-(±)-1,8,9,10,11,11-Hexachloropentacyclo[6.2.1.1^3,6.0^2,7.0^5,9]dodecan-4-ol (±)-7 and exo-(±)-1,8,9,10,11,11-hexachloropentacyclo[6.2.1.1^3,6.0^2,7.0^5,9]dodecan-4-ol (±)-4 have been prepared and the enantiomeric enrichment capacity of the lipase from Candida rugosa in the transesterification with vinyl acetate of these compounds was evaluated. It was verified that the lipase recognize only the alcohol (±)-7, producing endo-(+)-1,8,9,10,11,11-hexachloropentacyclo[6.2.1.1^3,6.0^2,7.0^5,9]dodecan-4-yl acetate (+)-8 with ee >95% and conversion of 44% as the only product.     

Studies on acid-catalysed σ-bond cleavage of aromatic conjugated cyclopropyl ketones: A new synthetic route to some hydroaromatic spiro compounds

Acid-catalysed cleavage of the aromatic conjugated cyclopropane σ-bond of the 3,4-benztricyclo[5.3.0^1,7.0^2,7]decan-10-one system has been studied and regioselective ring cleavage via the corresponding benzyl carbonium ion demonstrated giving rise to the respective spiro compounds.     

Chemistry of strained polycyclic compounds—IX: The synthesis and homoketonization of 4-substituted homocuneane acetates

The synthesis of three bridgehead homocuneanes acetates viz 1-bromopentacyclo [4.3.0.0^2.4.0^3.8.0^5.7]nonan-9-one ethylene ketal 4-acetate (10), 1-bromopentacyclo[4.3.0.0^2.4.0^3.8.0^5.7]nonane 4-acctate (22) and pentacyclo[4.3.0.0^2.4.0^3.8.0^5.7]nonane-9-one ethylene ketal 4-acetate (31) is described, starting from the readely available homocubane carboxylic acid (4). The base and acid catalyzed homoketonization reaction of these acetates has been studied. Under basic conditions the acetates (10, 22 and 31) are converted into tettacyclo[4.3.0.0^2.4.0^3.8]nonane derivatives by a cyclopropanol ring cleavage. This homoketonization reaction is a stereospecific process proceeding with retention of configuration. The effect of cage strain on the stereochemistry of base induced homoketonization of bridgehead cage alcohols is discussed.The acid catalyzed homoketonization of acetate (10) was also found to occur exclusively with retention of configuration.     

Hydrodefluorination of non-activated C-F bonds by diisobutyl-aluminiumhydride via the aluminium cation [i-Bu2Al]

A novel system for the hydrodefluorination (HDF) of non-activated C-F bonds at room-temperature is described. The reaction of i-Bu₂AlH with [Ph₃C][B(C₆F₅)₄] (1), [Ph₃C][Al(C₆F₅)₄] (2) and [Ph₃C][Al{OC(CF₃)₃}₄] (3) as precatalysts leads under formation of triphenylmethane to the aluminium cation [i-Bu₂Al]⁺ and the non-coordinating anions [M(C₆F₅)₄]⁻ (M = B, Al) and [Al{OC(CF₃)₃}₄]⁻. The formed aluminium cation is very reactive towards C-F bonds and easily forms i-Bu₂AlF releasing a carbocation that abstracts the hydride of excess i-Bu₂AlH and yields the corresponding hydrocarbon. Thereby, the active species [i-Bu₂Al]⁺ is regenerated and can realize a catalytic cycle. For 1-fluorohexane as an example including non-activated C-F bonds different activities were found (TON: 1: 20; 2: 12; 3: 30) in cyclohexane as solvent.     

Rhodauricanol A,an analgesic diterpenoid with an unprecedented 5/6/5/7 tetracyclic system featuring a unique 16-oxa-tetracyclo[11.2.1.01,5.07,13]hexadecane core from Rhododendron dauricum

A novel diterpenoid with an unprecedented 5/6/5/7 tetracyclic system, rhodauricanol A (1), five new grayanane-derived diterpenoids, dauricanols A?E (2?6), and five known ones (7?11) were isolated from the flowers of Rhododendron dauricum. Rhodauricanol A (1) possesses a unique 5/6/5/7 tetracyclic ring system featuring a 16-oxa-tetracyclo[11.2.1.0^1,5.0^7,13]hexadecane core. Dauricanols A?C (2?4) are the first 1,3-dioxolane conjugates of grayanane diterpenoids and 5-hydroxymethylfurfural and vanillin, respectively, and dauricanols D (5) and E (6) represent the first examples of 6-deoxy-1,5-seco-grayanane diterpenoids. Their structures were determined by spectroscopic methods, quantum chemical calculation including ¹³C NMR-DP4+ analysis and ECD calculation, and single-crystal X-ray diffraction analysis. Plausible biosynthetic pathways for 1?4 were proposed. All the isolates showed significant analgesic activities, and dauricanols B (3) and C (4) showed more potent analgesic activities than the positive control, morphine.     

Ruthenium monoterpyridine complexes with 2,6-bis(benzoxazol-2-yl)pyridine as an ancillary ligand: Synthesis,structure and spectral studies

Ruthenium monoterpyridine complexes, [1]⁺ and [2]²⁺, with 2,6-bis(benzoxazol-2-yl)pyridine as an ancillary ligand, L, have been synthesized and characterized by UV–Vis, FT-IR and ¹H NMR spectroscopic techniques. The formulations of the complexes were confirmed by the single crystal structure of their perchlorate salts. In both complexes, the Ru^II center is hexa-coordinated in a distorted geometry. In complex [1]⁺, the ancillary ligand L behaves as a bidentate ligand; in [2]²⁺, however, it binds the metal center as a tridentate ligand. The central pyridine nitrogen of terpyridine (N_p,trpy) is in a cis position with respect to the central pyridine nitrogen of the ancillary ligand (N_p,benz) in complex [1]⁺ and in a trans-position in complex [2]²⁺. The cis orientation of N_p,trpy and N_p,benz in complex [1]⁺ forces L to behave as bidentate. The quasi-reversible Ru^II/Ru^III couple appears at 0.90 and 1.44 V versus SCE in the case of complex [1]⁺ and [2]²⁺, respectively. [1]⁺, in the presence of aqueous AgNO₃, affords [2]²⁺ through an intramolecular dissociative interchange pathway.     

Ruthenium(II) and iron(II) complexes of N-pyridyl substituted imidazolin-2-ylidenes

N-mesityl-N′-pyridyl-imidazolium chloride 1a and the corresponding bromide salt 1b have been deprotonated with NaH in THF giving the free N-heterocyclic carbene N-mesityl-N′-pyridyl-imidazolin-2-ylidene 2 in 80% yield (starting from 1a). Imidazolium salt 1a reacts with RuCl₃ · xH₂O to give a racemic mixture of dinuclear di-μ-chloro bridged ruthenium complexes [(κ²-2)₂Ru(μ-Cl)₂Ru(κ²-2)₂]²⁺ [3a]²⁺. The carbene carbon atoms as well as the halides are arranged in cis-positions to each other whereas the nitrogen atoms adopt a trans-configuration. The di-μ-bromo bridged derivative [(κ²-2)₂Ru(μ-Br)₂Ru(κ²-2)₂]²⁺ [3b]²⁺ was obtained from RuCl₃ · xH₂O and 1b. The bridging halide ligands can be removed by the reaction with silver or sodium salts of bidentate Lewis acids. Complex [3a]²⁺ reacts with silver pyridylcarboxylate to give a racemic mixture of the mononuclear complex [4]⁺. Reaction of [3a]²⁺ with the sodium salt of l-proline resulted in a diastereomeric mixture of complexes [5]⁺. The free N-heterocyclic carbene 2 reacts with [FeCl₂(PPh₃)₂] to give after anion exchange with NaBPh₄ cis/cis/trans coordinated [Fe(κ²-2)₂(MeCN)₂](BPh₄)₂ [6](BPh₄)₂. The molecular structures of [3b](PF₆)₂, [4]PF₆ and [6](BPh₄)₂ · H₂O are reported.     

Homologues of N-heterocyclic carbenes: Detection and electronic structure of N-bridgehead pyrido[a]-anellated 1,3,2-diazagermol-2-ylidenes

Novel N-bridgehead pyrido[a]-anellated 1,3,2-diazagermol-2-ylidenes 1a,b were obtained from GeCl₂ · dioxane and dilithium reagents formed from N-tert-butyl pyridine-2-aldimines and excess lithium in THF whereas attempts to generate the analogous silylene by reduction of the dichloro-pyrido[a]-1,3,2-diazasilole 4a, synthesized from SiCl₄ and the new dilithium reagent, failed. Characteristic chemical shifts of the pyrido ¹H and ¹³C nuclei between those of pyridine compounds and the not fully cyclodelocalized electron-rich 4a with dihydropyridine substructure hint to a cyclodelocalized 10π electron system in 1a,b. Quantum chemical investigations of a series of pyrido[a]- and benzo-anellated imidazol-2-ylidenes and their silylene and germylene homologues show for all compounds cyclodelocalized 10π-systems but for pyrido[a]-anellation an increase of the energy of the π-MO’s relative to those of element(II) lone electron pairs which leads to destabilization compared to the benzo-anellated isomers.     

Highly active/selective and adjustable zirconium polymerization catalysts stabilized by aminopyridinato ligands

This paper describes a substantial enhancement of the aminopyridinato ligand stabilized early transition metal chemistry by introducing the sterically very demanding 2,6-dialkylphenyl substituted aminopyridinato ligands derived from (2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)-pyridin-2-yl]-amine (1a-H, ApH) and (2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-pyridin-2-yl]- amine (1b-H, Ap^∗H). The corresponding bis aminopyridinato zirconium dichloro complexes, [Ap₂ZrCl₂] (3a) and [Ap₂^∗ZrCl₂] (3b) and the dimethyl analogues, [Ap₂ZrMe₂] (4a) and [Ap₂^∗ZrMe₂] (4b) (Me = methyl) were synthesized, using standard salt metathesis routes. Single-crystal X-ray diffraction was carried out for the dichloro derivatives. Both zirconium metal centers have a distorted octahedral environment with a cis-orientation of the chloride ligands in 3a and a closer to trans-arrangement in 3b. The dimethyl derivatives are proven to be highly active ethylene polymerization catalysts after activation with [R₂N(Me)H][B(C₆F₅)₄] (R = C₁₆H₃₃-C₁₈H₃₇). During attempted co-polymerizations of α-olefins (propylene) and ethylene high activity and selectivity for ethylene and nearly no co-monomer incorporation was observed. Increasing the steric bulk of the ligand going from (2,6-dimethylphenyl) to (2,4,6-triisopropylphenyl) substituted pyridines, switches the catalyst system from producing long chain α-olefins to polymerization of ethylene in a living fashion. In contrast to the dimethyl complexes only [Ap₂^∗ZrCl₂] in the presence of MAO at elevated temperature gave decent polymerization activity. NMR investigations of the reaction of dichloro complexes with 25 equiv. of MAO or AlMe₃ at room temperature revealed, that [Ap₂ZrCl₂] decomposes under ligand transfer to aluminum and formation of [ApAlMe₂], while [Ap₂^∗ZrCl₂] remains almost unreacted under the same conditions. The aminopyridinato dimethyl aluminum complexes, [ApAlMe₂] (5a) and [Ap^∗AlMe₂] (5b) were synthesized independently and structurally characterized. The aluminum complexes 5a and b show no catalytic activity towards ethylene, when “activated” with[R₂N(Me)H][B(C₆F₅)₄].     

Ruthenium monoterpyridine complexes with 2,6-bis(benzimidazol-2-yl)pyridine: Synthesis,spectral properties and structure

Ruthenium monoterpyridine complexes with the tridentate 2,6-bis(benzimidazol-2-yl)pyridine (LH₂), [Ru(trpy)(LH₂)]²⁺, [1]²⁺ and [Ru(trpy)(L²⁻)], 2 (trpy = 2,2′:6′,2″-terpyridine) have been synthesized. The complexes have been authenticated by elemental analyses, UV–Vis, FT-IR, ¹H NMR spectra and their single crystal X-ray structures. Complexes [1]²⁺ and 2 exhibit strong MLCT band near 475 and 509 nm, respectively, and are found to be very much dependent on solution pH. The successive pH dependent dissociations of the N–H protons of benzimidazole moiety of LH₂ in [1]²⁺ lead to the formation of 2. The proton induced inter-convertibility of [1]²⁺ and 2 has been monitored via UV–Vis spectroscopy and redox features. The two pK_a values, 5.75 and 7.70, for complex [1]²⁺ have been determined spectroscopically.     

Cubane derivatives

The reduction of 1-bromo-9,9-ethylenedioxypentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonane-4-carboxylic acid (2) with lithium aluminum hydride and aluminum hydride in THF was studied. A new effective method for preparing 1-bromo-9,9-ethylenedioxypentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]-non-4-ylcarbinol (1) based on reduction of2 with AlH₃ under mild conditions was developed.     

Aminobis(phenolate)s of imidomolybdenum(VI) and -tungsten(VI)

The reactions of trans-[MoO(ONO^Me)Cl₂] 1 (ONO^Me = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) dianion) and trans-[MoO(ONO^tBu)Cl₂] 2 (ONO^tBu = methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate) dianion) with PhNCO afforded new imido molybdenum complexes trans-[Mo(NPh)(ONO^Me)Cl₂] 3 and trans-[Mo(NPh)(ONO^tBu)Cl₂] 4, respectively. As analogous oxotungsten starting materials did not show similar reactivity, corresponding imido tungsten complexes were prepared by the reaction between [W(NPh)Cl₄] with aminobis(phenol)s. These reactions yielded cis- and trans-isomers of dichloro complexes [W(NPh)(ONO^Me)Cl₂] 5 and [W(NPh)(ONO^tBu)Cl₂] 6, respectively. The molecular structures of 4, cis-6 and trans-6 were verified by X-ray crystallography. Organosubstituted imido tungsten(VI) complex cis-[W(NPh)(ONO^tBu)Me₂] 7 was prepared by the transmetallation reaction of 6 (either cis or trans isomer) with methyl magnesium iodide.     

Design and synthesis of fluorescent 6-aryl[1,2-c]quinazolines serving as selective and sensitive ‘on-off’ chemosensor for Hg in aqueous media

Three fluorescent quinazolines thiophen-2-yl-5,6-dihydrobenzo-[4,5]imidazo[1,2-c]quinazoline (1), pyridin-3-yl-5,6-dihydrobenzo-[4,5]imidazo-[1,2-c]quinazoline (2) and phenyl-5,5′,6,6′-dihydrobenzo-[4,4′,5,5′]imidazo-[1.1′,2-c,2′-c]quinazoline (3) have been synthesized. Structures of 1 and 3 have been authenticated crystallographically. Quinazolines 1-3 exhibit highly selective ‘on-off’ switching for Hg²⁺ ions. The fluorescence intensity displayed a linear relationship with respect to Hg²⁺ concentration (0.1-1.0 μM; R² = 0.99) with detection limit of 2.0 × 10⁻⁷ M.     

Regulation of electron donating ability to metal center: isolation and characterization of ruthenium carbonyl complexes with N,N- and/or N,O-donor polypyridyl ligands

Polypyridyl ruthenium(II) dicarbonyl complexes with an N,O- and/or N,N-donor ligand, [Ru(pic)(CO)₂Cl₂]⁻ (1), [Ru(bpy)(pic)(CO)₂]⁺ (2), [Ru(pic)₂(CO)₂] (3), and [Ru(bpy)₂(CO)₂]²⁺ (4) (pic=2-pyridylcarboxylato, bpy=2,2′-bipyridine) were prepared for comparison of the electron donor ability of these ligands to the ruthenium center. A carbonyl group of [Ru(L1)(L2)(CO)₂]ⁿ (L1, L2=bpy, pic) successively reacted with one and two equivalents of OH⁻ to form [Ru(L1)(L2)(CO)(C(O)OH)]ⁿ⁻¹ and [Ru(L1)(L2)(CO)(CO₂)]ⁿ⁻². These three complexes exist as equilbrium mixtures in aqueous solutions and the equilibrium constants were determined potentiometrically. Electrochemical reduction of 2 in CO₂-saturated CH₃CN–H₂O at −1.5 V selectively produced CO.     

Copper(II) complexes of N(4)-substituted thiosemicarbazones derived from pyridine-2-carbaldehyde: Crystal structure of a binuclear complex

Ten copper(II) complexes {[CuL¹Cl] (1), [CuL¹NO₃]₂ (2), [CuL¹N₃]₂ · 2/3H₂O (3), [CuL¹]₂(ClO₄)₂ · 2H₂O (4), [CuL²Cl]₂ (5), [CuL²N₃] (6), [Cu(HL²)SO₄]₂ · 4H₂O (7), [Cu(HL²)₂] (ClO₄)₂ · 1/2EtOH (8), [CuL³Cl]₂ (9), [CuL³NCS] · 1/2H₂O (10)} of three NNS donor thiosemicarbazone ligands {pyridine-2-carbaldehyde-N(4)-p-methoxyphenyl thiosemicarbazone [HL¹], pyridine-2-carbaldehyde-N(4)-2-phenethyl thiosemicarbazone [HL²] and pyridine-2-carbaldehyde N(4)-(methyl), N(4)-(phenyl) thiosemicarbazone [HL³]} were synthesized and physico-chemically characterized. The crystal structure of compound 9 has been determined by X-ray diffraction studies and is found that the dimer consists of two square pyramidal Cu(II) centers linked by two chlorine atoms.