Aryl-aryl coupling reaction using a novel and highly active palladium reagent prepared from Pd(OAc)2, 1,3-bis[diphenylphosphino]propane (DPPP), and Bu3P

A palladium-assisted coupling reaction of aryl triflate with arene was investigated, and a novel Pd reagent prepared from equimolar Pd(OAc)2, 1,3-Bis[diphenylphosphino]propane (DPPP), and Bu3P was developed. This method is useful for intramolecular biaryl coupling reactions, not only between aryl triflate and arene (triflate-amide), but also between aryl halide and arene (halo-amide).     

On the electronic character of localized singlet 2,2-dimethoxycyclopentane-1,3-diyl diradicals: substituent effects on the lifetime

Photodenitrogenation of the diazenes 4 affords exclusively the housanes 5 through intramolecular cyclization of the spectrally detected and characterized singlet diradicals 3. The lifetime of singlet diradical 3, determined by transient absorption measurements, depends on the Y and Z substituents at the para position of the phenyl ring and has the following order: Y, Z = OMe, OMe > OMe, CN > CN, CN > OMe, H > Cl, Cl approximately CN, H approximately Me, Me > H, H. This unprecedented substituent effect reveals stabilization of the singlet 2,2-dimethoxycyclopentane-1,3-diyl diradicals 3 through radical, zwitterionic, pi-bonding, and hyperconjugative structures.     

Synthetic approach to natural products by Claisen rearrangement of glyceraldehyde derivatives

For the purpose of organic syntheses of some corynanthe-type indole alkaloids, sesquiterpenes, and steroids, optically active intermediates cyclopentanone 3-allylalcohol, α-methylene-γ-butylo lactones andtrans-hydrindanone-propionic acid, were synthesized from (R)- and (S)-isopropylideneglyceraldehyde derived fromD-mannitol andLascorbic acid, respectively, utilizing Claisen rearrangement as a key reaction. Actually total syntheses of natural alkaloids, (-)-antirhine, (+)-dihydroantirhine and (-) dihydrocorynantheol were accomplished.     

Analysis of novel imidazoles from isolated perfused rabbit heart by two high-performance liquid chromatographic methods.

The paper reports two analytical high-performance liquid chromatographic methods to detect and quantify cardiac-derived histidyl derivatives. Method A relies on relative hydrophobicities as a basis of separation. Method B is an ion-pairing method in which the compounds are eluted in an entirely different order. Fractions collected from method A have been co-eluted in admixture in method B with authentic reference compounds. Thus the existence of the following imidazole ring-containing compounds derived from heart have been confirmed: N-acetylhistidine, N-acetyl-1-methylhistidine, N-acetylcarnosine, N-acetylhomocarnosine, homocarnosine, anserine, carnosine, balenine. Compounds were found in both tissue samples and perfusates.     

Synthesis and photochemical properties of a photochromic iron(II) complex of hexaarylbiimidazole

The photochromic ligand bis(terpyridyl)hexaarylbiimidazole (bistpy-HABI) and the Fe(II) complex of bistpy-HABI with formula [{Fe(tpy)}2.bistpy-HABI](PF6)4.4H2O were synthesized and characterized. Bistpy-HABI is readily cleaved into a pair of terpyridyltriphenylimidazolyl radicals (tpy-TPI*) on irradiation with UV light. This photochemical reaction is completely reversible, and the light-induced radicals can thermally recombine to form bistpy-HABI in the dark. [{Fe(tpy)}2.bistpy-HABI]4+ is the first example of a transition-metal complex of an HABI derivative and was found to show photochromic reaction in solution. The spin state of the light-induced radical pair in a frozen matrix was investigated by ESR spectroscopy. The triplet state of the light-induced radical pair from [{Fe(tpy)}2.bistpy-HABI]4+, as well as that from bistpy-HABI, was confirmed to be a ground state or nearly degenerated with a singlet state. Kinetic studies on the radical recombination reaction in solution elucidated the decrease in the activation energy by forming the Fe(II) complex. This is the first observation of a decrease in the activation energy of the radical recombination reaction by the formation of a metal-coordinated radical complex. The syntheses, photochemical properties, and spin states of bistpy-HABI and [{Fe(tpy)}2.bistpy-HABI](PF6)4 are discussed.     

EFFECTS OF EXTRACELLULAR Ca2+ CONCENTRATION AND PAPAVERINE ON THE VISUAL CELL FUNCTION IN THE ISOLATED FROG RETINA

Abstract— Effects of extracellular Ca²⁺ concentration and papaverine on the PIII response of the electroretinogram and the dark adaptation process of the visual cells were studied in the isolated, aspartate-treated bullfrog retina. The amplitudes of both the fast and slow PIII responses are increased in 0.01 m M Ca²⁺ solution, but decreased in Ca²⁺-free solution containing 1 m M EDTA. The application of 0.1 m M papaverine in the presence of 1 m M Ca²⁺ led to the enhancement of the slow PIII response at lower stimulus intensity and the prolongation of the slow PIII response, but these effects of papaverine on the response were lost when Ca²⁺ was removed from the bathing fluid. The half-time of recovery of the fast PIII response amplitude after switching off the adapting light was a linear function of the amount of bleached rhodopsin. Papaverine in the absence of Ca²⁺ produced about 2-fold increase in the half-time of recovery of the response. These findings suggest that chemical reactions which are sensitive to papaverine in the absence of Ca²⁺ are implicated in the dark adaptation process of the visual cells.     

Simons electrochemical fluorination of substituted homopiperazines(hexahydro-1,4-diazepines) and piperazines

Simons electrochemical fluorination (ECF) of 1,4-dimethyl-1,4-homopiperazine, methyl 4-ethylhomopiperazin-1-ylacetate and 1,4-bis(methoxycarbonylmethyl)-1,4-homopiperazine was studied. For comparison, ECF of three piperazines with a N-(methoxycarbonylmethyl) group(s) was also studied. ECF of 1,4-dimethyl-1,4-homopiperazine gave a low yield of corresponding perfluoro(1,4-dimethyl-1,4-homopiperazine) together with perfluoro(2,6-diaza-2,6-dimethylheptane) as the major product. Corresponding perfluoro(homopiperazines) with mono- and/or di-(fluorocarbonyldifluoromethyl) groups [CF₂C(O)F] at the 1- and/or 4-position were formed in low yields from methyl 4-ethylhomopiperazin-1-ylacetate and 1,4-bis(methoxycarbonylmethyl)-1,4-homopiperazine, respectively. These new seven-membered perfluoro(1,4-dialkyl-1,4-homopiperazines) were accompanied by the formation of mono- and/or di-basic linear perfluoroacid fluorides resulting from the CC bond scission at the 2- and 3-positions of the ring. From mono- and/or di-N-(methoxycarbonylmethyl)-substituted piperazines, corresponding perfluoropeperazines having the acid fluoride group(s) were formed in low yields.     

Preparation of polysiloxanes from silicic acid. III. Preparation and properties of polysilicic acid butyl esters

Polysilicic acid butyl esters were prepared from 1-butanol and silicic acid extracted from sodium metasilicate solution and water glass with tetrahydrofuran and hydrochloric acid. The properties of the esters were dependent on the degree of esterification (DE). The esters with a DE of less than ca. 60% could be isolated by precipitation with hexane and were highly liable to self-condensation, whereas those with more than 60% DE were soluble in solvents and could not be precipitated easily. They underwent further condensation to form highly polymerized esters. Subsequent silylation allowed the isolation and characterization of these esters. The solvent-soluble silylated esters had moderate thermal stability with decomposition points between 210 and 260°C and number-average molecular weights of 10,000–30,000. From the evaluation of units structures of silylate it was suggested that polymer backbone was a pseudoladder structure.     

Snytheses of analgesics. Part XXXVII. An alternative synthesis of 1,2,3,4, 5, 6-hexahydro-8-hydroxy-2,6-methano-6, h-dimethyl-3-phenethyl-3-benzazoeine [studies on the syntheses of heterocyclic compounds. Part DXXI]

Acid treatment of the alkylated products of (Va, Vb, and VIII) of piperidinols IVa and IVb, and tetrahydropyridine VII with β-bromoethylbenzene, afforded 1,2,3,4,5,6-hexahydro-8-hydroxy-2,6-methano-6,1 1-dimethyl-3-phenethyl-3-benzazocine (la) in good yield. Piperidinols Va and Vb were also obtained from the reaction of N-(3-methyl-3-pentenyl)-β-phenethylamine (IIb) with methyl 3-(4-methoxyphenyl)-2,3-epoxypropionate.