Synthesis of pyrazoles and condensed pyrazoles

This review introduces the synthesis of various pyrazoles reported by us and some other research groups during 1989–1998. Some of papers in this review deal with the development of potent pyrazoles or with the synthesis of potential pyrazoles aiming at agrochemicals and/or drugs.     

Exact Averaging of Stochastic Equations for Flow in Porous Media

It is well-known that at present, exact averaging of the equations for flow and transport in random porous media have been proposed for limited special fields. Moreover, approximate averaging methods—for example, the convergence behavior and the accuracy of truncated perturbation series—are not well-studied, and in addition, calculation of high-order perturbations is very complicated. These problems have for a long time stimulated attempts to find the answer to the question: Are there in existence some, exact, and sufficiently general forms of averaged equations? Here, we present an approach for finding the general exactly averaged system of basic equations for steady flow with sources in unbounded stochastically homogeneous fields. We do this by using (1) the existence and some general properties of Green’s functions for the appropriate stochastic problem, and (2) some information about the random field of conductivity. This approach enables us to find the form of the averaged equations without directly solving the stochastic equations or using the usual assumption regarding any small parameters. In the common case of a stochastically homogeneous conductivity field we present the exactly averaged new basic non-local equation with a unique kernel-vector. We show that in the case of some type of global symmetry (isotropy, transversal isotropy, or orthotropy), we can for three-dimensional and two-dimensional flow in the same way derive the exact averaged non-local equations with a unique kernel-tensor. When global symmetry does not exist, the non-local equation with a kernel-tensor involves complications and leads to an ill-posed problem.     

Theoretical study on decomposition of γ-halo allylalkoxide and β-halo acrylate ions

β, γ-Substituted γ-halo allylalkoxide ions decompose to form a halogen ion, formaldehyde, and an alkyne under mild conditions, for example at room temperature. The E isomer does not differ from the Z isomer in terms of activation energy. We attempted to shed light on the mechanism of the reaction by using ab initio molecular orbital calculations. The observed propensity was confirmed by the present calculation on model molecules, γ-chloro allylalkoxide ions. We conducted further calculations and compared the alkoxide results with a similar reaction of β-haloacrylate ions that release carbon dioxide instead of formaldehyde. This similar reaction needs heating as high as 150°C. The activation energy of the acrylate ions (36–39 kcal mol⁻¹) was calculated to be about 10 kcal mol⁻¹ higher than that of the alkoxide ions. The activation energy of the E acrylate ion is smaller by 0.8 kcal mol⁻¹ than that of the Z isomer at the MP2/6-31+G**//RHF/6-31+G* level of theory. This is consistent with experimental results. While the ready deprotonation from the carboxylic group does not activate the acrylate ion very much, the alkoxide ion is destabilized to a great degree in the process of anion formation. The difficulty in deprotonation that proceeds from the neutral molecule is seen in the difference in the activation energies for the decomposition of the corresponding anions. Therefore, the pK _a of a hydroxy or a carboxylic group plays the leading role in determining the magnitude of activation energies of allyl halides with a negatively charged fragment. Received: 2 July 1998 / Accepted: 9 September 1998 / Published online: 8 February 1999     

Mechanism of NOH2 reaction over Rh foil and the role of chemisorbed nitrogen atoms

The behaviour of adsorbed nitrogen and the overall catalytic reaction between NO and H₂ on Rh foil were investigated in a pressure region around 10^?5–10^?4 Pa and a temperature range between 400 and 1200 K, using the flash desorption technique and ultraviolet photoelectron spectroscopy. In a reducing condition, the NOH₂ reaction proceeded rapidly in the temperature range between 500 and 1000 K, and the reaction probability of NO was almost unity in the temperature region studied. The major product was N₂, but NH₃ was also formed around 500 K. Chemisorbed nitrogen was accumulated during the NO-H₂ reaction and also during the NH₃ decomposition reaction. In both cases, the dependence of the rate of N₂ formation upon the amount of N(ad) estimated during the reaction was similar to that in the case of N(ad) flash desorption, which indicates that N₂ is formed by recombination of N(ad) in both the NO-H₂ reaction and the NH₃ decomposition reaction. The rate constant for the second order desorption of N(ad) was estimated to be $\text{10}{}^{\mathrm{?6.8\; \pm \; 0.3}}\text{exp(?97 ± 5(}\text{kJ}\text{mol}\text{) RT) (}\text{cm}{}^2\text{atom·s)}$. The overall reaction of NO-H₂ on Rh proceeds in a similar manner to Pd previously reported, but the dissociation of NO takes place more easily over Rh and O(ad) is more stable, being liable to cause an inhibition of the NO-H₂ reaction, especially at lower temperature.     

Ab initio molecular orbital study on inversion mechanism of trimethylene bridges of [33](1,3,5)- and [36](1,2,3,4,5,6)cyclophanes

Ab initio molecular orbital (MO) study on the inversion process of six trimethylene bridges between two degenerate C_6h conformers of [3₆](1,2,3,4,5,6)cyclophane suggests that the inversion occurs in a stepwise manner rather than a synchronous mechanism.     

Synthesis of pyrazoles

This review summarizes the synthesis of various pyrazoles reported by us and some other research groups in 1981–1989.     

Cholesterol-armed cyclens for helical metal complexes offering chiral self-aggregation and sensing of amino acid anions in aqueous solutions

Cholesterol-armed cyclens worked as octadentate receptors for Na+, Ca2+, and Y3+ complexes in which four chiral cholesterol-functionalized sidearms were bundled and asymmetrically twisted above cyclen-metal complex platforms. Since the resulting helical metal complexes included chiral, hydrophobic cholesterol residues and charged, hydrophilic metal sites as well as asymmetric coordination geometries, they exhibited unique amphiphilic properties and provided chiral self-aggregates in aqueous solutions. Light scattering, fluorescence, and TEM characterizations demonstrated that Na+ complex with cholesterol-armed cyclen gave a particularly stable self-aggregate in aqueous solution and offered supramolecular environments effective for sensing and detection of amino acid anions. Various dansylamino acid derivatives (dansyl = 5-(dimethylamino)-1-naphthalenesulfonyl) were nicely accommodated in the helicate aggregates to give highly enhanced fluorescence signals, which could be detected by the naked eye at 10(-7) mol/L level. Their inclusion behaviors were analyzed by a Langmuir-type equation, indicating that enantiomer-selective inclusion occurred. MM/MD calculations and circular dichroism (CD) studies further suggested that cholesterol-armed cyclen helicates have chiral and hydrophobic cavities upon self-aggregation, in which the dansylamino acid anions were specifically accommodated. Since these helicates exhibited nonselective binding abilities in solvent extraction experiments of dansylamino acid anions, uncommon chiral recognition and sensing functions were generated by supramolecular alignments of the chiral metal helicates in the aqueous solutions.