Reactions of zirconacyclopentadienes with C [double bond] ), C [double bond] N, and N [double bond] N moieties with electron-withdrawing groups: formation of six-membered heterocycles

Reactions of zirconacyclopentadienes with diethyl ketomalonate gave alpha-pyrans in excellent yields in the presence of BiCl3. In the absence of BiCl3, zirconacyclopentadienes did not react with diethyl ketomalonate. Tetraphenylzirconacyclopentadiene reacted with diethyl ketomalonate in the presence of BiCl3 to give a ring-opening product, dienolic ether, in 53% yield. The structures of the alpha-pyran prepared from diethyldiphenylzirconacyclopentadiene and the ring-opening product were determined by X-ray analysis. When oximinosulfonate was added to tetraethylzirconacyclopentadiene in THF at -78 degrees C, 3,4,5,6-tetraethylpyridine-2-carbonitrile was obtained in 95% yield within 10 min. The structure of the product was confirmed by X-ray analysis. When tetraethylzirconacyclopentadiene was treated with azodicarboxylate in the presence of 2 equiv of CuCl at -78 degrees C, 1,2-dialkoxycarbonyl-3,4,5,6-tetraethyl-1,2-dihydropyridazine derivatives were obtained. The structure of one of dihydropyridazine was also confirmed by X-ray analysis.     

Oxidation-active flavin models: oxidation of alpha-hydroxy acids by benzo-dipteridine bearing metal-binding site in the presence of divalent metal ion and base in organic solvents.

The oxidizing ability of benzo-dipteridine bearing a bipyridin-6-ylmethyl moiety (4) was found to be increased with Zn(2+) by approximately 10(3)-fold for sulfite addition in MeOH and approximately 10(2)-fold for oxidation of an NADH model in MeCN. It was found for the first time that 4 is able to oxidize alpha-hydroxy acids to alpha-keto acids in the presence of a divalent metal ion such as Zn(2+), Co(2+), and Ni(2+) and an amine base in MeCN or t-BuOH, whereas benzo-dipteridine having a bipyridin-5-ylmethyl moiety (3) is unable to oxidize them under the same conditions. The oxidation reaction was kinetically investigated including the kinetic isotope effect for deuterated mandelic acids (k(H)/k(D) = 2.1-3.7) and the Hammett plots for substituted mandelic acids (V-shaped plots). In the reaction of alpha-substituted alpha-hydroxy acids such as alpha-methyl mandelic and benzylic acids with 4, novel oxidative decarboxylation was found to take place, giving acetophenone and benzophenone, respectively. The oxidation mechanism for mandelic acid was proposed to proceed via a ternary complex of 4.Zn(2+).PhCH(OH)CO(2)(-), in which alpha-oxyanion of mandelate attacks C(4a)-position of 4 to form an adduct followed by 1,2-elimination to afford benzoyl formate and 2e-reduced 4. The roles of the metal ion were proposed as follows; (i) activation of 4, (ii) substrate-binding site, and (iii) activation of the bound alpha-hydroxy acid by lowering pK(a)'s of alpha-OH and alpha-CH. This is a first example that a flavin model oxidizes alpha-hydroxy acids in the presence of a metal ion.     

One-pot isomerization of aldo-disaccharides to keto-disaccharides in deep sea water under sub-critical conditions

A novel and facile one-pot isomerization of aldo-disaccharides to keto-disaccharides is achieved by making use of deep sea water in sub-critical conditions. The resulting keto-disaccharides having pharmaceutical and food applications were obtained in modest yields of about 30–32% at the optimum reaction conditions (temperature: 180 °C, reaction time: 5 min). Detailed investigation of all major ions in deep sea water revealed that bicarbonate ions play a key role as a catalyst in this isomerization reaction.     

High pressure effect on the electrical properties of NiS2

A semiconductor-metal transition in the electrical resistance of NiS₂, which has been suggested to be a Mott transition, is observed with decreasing temperature under pressure up to 44 kbar. The transition temperature increases with pressure with a slope of $\text{dT}\text{dP}\text{= 6 ± 1 K/kbar}$. The activation energy in a semiconducting region is found to decrease with increasing pressure and to vanish at about 46 kbar. The critical pressure and temperature are predicted to be 46 ± 2 kbar and 350 ± 20 K.     

Total Synthesis of (+)‐MPC1001B

The first total synthesis of an epidithiodiketopiperazine alkaloid, (+)‐MPC1001B, was accomplished. This synthesis features a tetra‐n‐butylammonium fluoride mediated intramolecular aldol reaction for forming the 15‐membered macrolactone ring, and the construction of an epidithiodiketopiperazine substructure through a stepwise sulfenylation reaction involving a novel trityl trisulfide (TrSSS)‐group transfer.     

Efficient peroxide decoloration of azo dye catalyzed by polyethylene glycol-linked manganese chlorin derivative

We reported here that polyethylene glycol (PEG)-linked manganese pyrochlorophyllide a (PEG-MnPChlide a) possesses remarkable catalytic activity comparable to horseradish peroxidase (HRP). The PEG-MnPChlide a catalyzed the oxidation decoloration reaction of C.I. Acid Orange 7 by hydrogen peroxide under a mild aqueous condition, pH 8.0 at 25 °C. The manganese pyrochlorophyride a methylester (MnPChlide a ME) dissolved in a Triton X-100 micellar solution also exhibited the catalytic activity, indicating the micellar environment plays an important role in the catalytic reaction. The reaction rate was accelerated by addition of imidazole. The catalytic reactions were analyzed by Michaelis–Menten kinetics, revealing that the higher reactivity of catalyst–substrate complex is responsible for the present catalytic reaction system.     

Large positive magnetoresistance of insulating organic crystals in the non-ohmic region

We report a large positive magnetoresistance ratio in insulating organic crystals theta-(ET)(2)CsZn(SCN)(4) at low temperatures at which they exhibit highly nonlinear current-voltage characteristics. Despite the nonlinearity, the magnetoresistance ratio is independent of the applied voltage. The magnetoresistance ratio depends little on the magnetic field direction and is described by a simple universal function of mu(B)B/k(B)T, where mu(B) is the Bohr magneton. The positive magnetoresistance may be caused by magnetic-field-induced parallel alignment of spins of mobile and localized electrons, and a resulting blockade of electrical conduction due to the Pauli exclusion principle.