Palladium-catalyzed oxidation of cyclohexanones to conjugated enones using molecular oxygen

Oxidation of cyclohexanones into conjugated enones with molecular oxygen as oxidant was achieved by palladium catalysts. A catalyst system consists of 1 mol % Pd(OCOCF₃)₂ and 5,5′-dimethyl-2,2′-bipyridine accomplished maximum 84% yield for the oxidation of cyclohexanone and 51-78% yields for 4-substituted-cyclohexanones.     

Quantitative structure-activity relationship study of N-(3-oxo-3,4-dihydro-2H-benzo[1,4]thiazine-6-carbonyl)guanidines as potent Na/H exchange inhibitors

We have previously reported that N-(4-isopropyl-2,2-dimethyl-3-oxo-3,4-dihydro-2H-benzo[1,4]oxazine-6-car bonyl)guanidine (4b) methanesulfonate salt (KB-R9032) is a potent and highly water-soluble Na/H exchange inhibitor. In a series of studies on Na/H exchange inhibitors, we designed and synthesized N-(3-oxo-3,4-dihydro-2H-benzo[1,4]thiazine-6-carbonyl)guanidines (5) as more potent inhibitors with high water-solubility. The design strategy for 5 was based on a quantitative structure-activity relationship (QSAR) study, involving the proportional relationship between the biological activity and hydrophobicity of the ring structure of compounds 4. As expected, compounds 5 showed more potent activity than 4. It was found by using the QSAR analysis that 5 were about five-fold more potent than 4. The increase in potency of compounds 5 well agreed with our previous QSAR analysis result. The most potent derivative was the methanesulfonate salt 5d of the 4-isopropyl derivative (IC50=0.0091 microM). And in addition to the in vitro study, 5d showed significant protective activity against a rat acute myocardial infraction model.     

Organic electroluminescent device with an aromatic amine-containing polymer as a hole transport layer (I): Poly[N-[p-N′ -phenyl-N′-[1,1′-biphenyl-4′-[N″-phenyl-N″-(2-methylphenyl)amino]-4-amino]]phenyl methacrylamide]

Electroluminescent devices were fabricated using a holetransporting polymer, poly[N-[p-N′ -phenyl-N′-[1,1′-biphenyl-4′-[N″-phenyl-N″-(2-methylphenyl)amino]-4-amino]]phenyl methacrylamide] (PTPDMA), and tris(8-quinolinolato)aluminum(III) complex, Alq, as the hole transport layer and the emitter layer, respectively. A device structure of glass substrate/indium–tin–oxide/PTPDMA/Alq/Mg:Ag was employed. Hole injection from the electrode through the PTPDMA layer to the Alq layer and concomitant electroluminescence from the Alq layer were observed. Bright green luminescence with a luminance of 20,000 cd/m² was obtained at a drive voltage of 14 V.     

Dissolution and bioavailability of phenobarbital in solid dispersion with phosphatidylcholine.

The dissolution of phenobarbital (PB) from solid dispersion with phosphatidylcholine (PC) was studied. PB was present in an amorphous state in solid dispersion (PB-PC) if the mole fraction of PB was under 0.75. Thus, supersaturation was observed when an excess amount of PB-PC was dispersed in pH 1.2 and 6.8 media. The degree of supersaturation was largest when the mole fraction of PB was 0.25, although it was only 1.3-fold of the PB solubility in this case. Dissolution from PB-PC was rapid and complete in both pH 1.2 and 6.8 media regardless of the mole fraction of PB, above 90% within 5 min. Bioavailability after the oral administration of PB-PC to rabbits with a dose of 15 mg/kg equivalent to PB was compared with that of PB crystals. The area under the plasma concentration curve was bigger, but not significant. The maximum concentration was significantly higher, and the time to maximum concentration was significantly faster. These results indicate that the absorption rate became high with PB-PC because the dissolution was rapid.     

Enantioselective Lewis acid-catalyzed Mukaiyama-Michael reactions of acyclic enones. Catalysis by allo-threonine-derived oxazaborolidinones

allo-Threonine-derived O-aroyl-B-phenyl-N-tosyl-1,3,2-oxazaborolidin-5-ones 1g,n catalyze the asymmetric Mukaiyama-Michael reaction of acyclic enones with a trimethylsilyl ketene S,O-acetal in high enantioselectivity. A range of alkenyl methyl ketones is successfully employed as Michael acceptors affording ee values of 85-90% by using 10 mol % of the catalyst. The use of 2,6-diisopropylphenol and tert-butyl methyl ether as additives is found to be essential to achieve high enantioselectivity in these reactions. The effects of the additives are discussed in terms of the retardation of an Si(+)-catalyzed racemic pathway, which seriously deteriorates the enantioselectivity of asymmetric Mukaiyama-Michael reactions. A working model for asymmetric induction is proposed based on correlation between catalyst structures and enantioselectivities.     

Kinetic control of threading of cyclodextrins onto axle molecules

We report here, for the first time, kinetic control of the face-direction of cyclodextrin (CD) in the construction of a pseudo-rotaxane with an alkyl chain bearing pyridyl end caps. The yields of complexes of CDs with guest alkyl derivatives were controlled by the simple change of the position and the number of methyl groups bound to the pyridyl moiety. Single-substituted pyridyl groups attached to the ends of the alkyl chain regulated the rate for CDs passing them. Two methyl substituents could clearly govern the degree of complex formation of CD with guest molecules and resulted in the distinction of face-direction of CD molecules entering the gates at guest ends.     

Viscosity of polydimethylsiloxane–pentamer systems

Viscosities of polydimethylsiloxane–pentamer systems were measured over the whole range of concentration. Twelve samples having molecular weights from about 1000 to 5 × 10⁵ were studied. The empirical reduction scheme, plots of log η versus log _cM^0.68, suggested by Ferry and co-workers is applicable to samples of M?_v ≥ 22,000 over the entire concentration. Such satisfying superposition of data may be attributed to the systems being the homologous mixtures in which glass temperatures of polymers are very low. On the basis of the treatment of Fox and Allen, the effects of the number and weight-average molecular weight on viscosity were examined, and the friction coefficient ζ per chain atom at constant M?_n was calculated over a wide range of M?_n. The value ζ is almost constant (ζ = 7.4 × 10^?9 dyne-sec./cm.) in the region of M?_n ≥ M_c, and where otherwise it decreases rapidly with decreasing M?_n. The length of the chainend segment was tentatively calculated.     

Synthesis and redox behavior of azulene-substituted benzene derivatives and (eta(5)-cyclopentadienyl)[tetra- and di(6-azulenyl)cyclobutadiene]cobalt complexes

1,2-Di(6-azulenyl)tetraphenylbenzenes and (6-azulenyl)pentaphenylbenzenes were synthesized by Diels-Alder reactions of di(6-azulenyl)acetylenes and 6-(phenylethynyl)azulenes with tetraphenylcyclopentadienone. Cobalt-mediated cyclooligomerization of mono- and di(6-azulenyl)acetylenes afforded 1,3,5- and 1,2,4-tri(6-azulenyl)benzene derivatives together with (eta(5)-cyclopentadienyl)[tetra- and di(6-azulenyl)cyclobutadiene]cobalt complexes. The redox behavior of these novel (6-azulenyl)benzene derivatives and [tetra- and di(6-azulenyl)cyclobutadiene]cobalt complexes was examined by cyclic voltammetry (CV). Mono(6-azulenyl)benzenes exhibited a reduction wave upon CV. In contrast, 1,2-di(6-azulenyl)benzenes showed a two-step reduction wave at the similar potential region upon CV, which revealed the formation of a dianion stabilized by 6-azulenyl substituents under electrochemical reduction conditions. Three 6-azulenyl substituents on benzene in a 1,2,4 relationship also increased electron-accepting properties because of the formation of a closed-shell dianionic structure, whereas 1,3,5-tri(6-azulenyl)benzenes were reduced stepwise.     

Modification of PVC. XXVI. Syntheses and photocrosslinking of polysulfide pendant poly(vinyl chloride)

Poly(vinyl chloride) pendant with polysulfide (PS–PVC) having various degrees of substitution, various S substituents, and various numbers of atoms in the sulfur chain has been synthesized by the reaction of poly(vinyl chloride) with a thiol, sulfur, and triethylamine in dimethylformamide at 30°C for 0.4–5 hr. The photocrosslinking reaction has been investigated under ultraviolet irradiation at 250–450 mμ. The photocrosslinking reaction of PS–PVC is influenced by the degree of substitution, the nature of the S substituent, and the number of atoms in the sulfur chain. The degree of photocrosslinking r increased in the order, n-C₄H₉? < n-C₈H₁₇? < C₆H₅CH₂? < i-C₃H₇? < t-C₄H₉? . On the photocrosslinking of PS–PVC having two different S substituents, r increases in the similar order for aliphatic substituents and in the order NO₂C₆H₄? < ClC₆H₄? < C₆H₅CH₂? < CH₃C₆H₄? < t-C₄H₉C₆H₄? < C₆H₅? for the aromatic substituents. Further, r increases markedly with the increase of sulfur chain number for all PS–PVC. The chemical structure of the crosslinks and the crosslinking mechanism are discussed on the basis of the results.     

Convergent synthesis of the E'FGH ring fragment of ciguatoxin 1B via an acetylene cobalt complex strategy

A convergent synthesis of the E'FGH ring fragment 28 of ciguatoxin 1B, a principal toxin causing widespread seafood poisonings "ciguatera", has been accomplished through (i) coupling between the E' ring-acetylide 9 and the H ring-aldehyde 20, (ii) stereoselective F ring cyclization via an acetylene cobalt complex, (iii) conversion to a carbonyl function under high-pressure hydrogenation, and (iv) reductive hydroxyketone cyclization to construct the G ring. In the (1)H NMR analysis of 28 at room temperature, a considerable broadening phenomenon was observed due to the slow conformational changes of the FG ring, as reported for natural ciguatoxin 1B. When measured in pyridine at -20 degrees C, the spectra of 28 exhibited a 3.5:1 mixture of two conformational isomers (UP and DOWN conformers).