Cyclic cotrimerization of an alkyne, an alkene, and carbon monoxide mediated by dicobalt octacarbonyl, which is well known as the Pauson-Khand reaction, was promoted by the addition of certain Lewis bases. Primary amines with secondary alkyl groups, such as cyclohexylamine, promoted the stoichiometric Pauson-Khand reaction to give the desired cyclopentenones in good yields. The same reaction can be conveniently carried out in 1, 4-dioxane-aqueous NH4OH biphasic system. Some reactive cobalt complexes might be produced as the coproduct in the reaction mixture and decomposed the substrate and/or the product in some cases. To overcome this disadvantage, alkyl methyl sulfides were introduced as the promoter. The catalytic Pauson-Khand reaction was also promoted by the addition of a tiny amount of DME or water. A novel decomplexation method of alkyne-dicobalt hexacarbonyl complexes by using ethylenediamine and a hydrocarbamoylation reaction were also presented.
New and useful reactions utilizing the characteristics of gem-dihalocyclopropanes and halocyclopropanes are developed from the many-sided cationic approaches toward versatile benzannulations. Regioselective and alternative naphthalene-benzannulations of aryl (gem-dihalogenocyclopropyl) methanols and Aryl1 (aryl2) (gem-dichlorocyclopropyl) methanols were performed for the syntheses of various types of both “symmetrically” and “unsymmetrically” substituted and α-and β-halogenonaphthalenes by choosing either the order of the reaction sequences or the catalysts. Sequential and regioselective Friedel-Crafts reactions (naphthol-benzannulations) of gem-dichlorocyclopropanecarbonyl chlorides produced various 4-aryl-1-naphthol derivatives straightforwardly (in a one-pot manner) via significantly different mechanisms from the related naphthalene-benzannulations. These utilities could be demonstrated by the total synthesis of five natural lignan lactones and their analogs. A related 2, 5-diaryl-furan syntheses, a novel cyclopropane-shift type benzannulation, and a unique chirality transfer from optically active gem-dichlorocyclopropanes into atropisomeric 1-arylnaphthalenes were also described. The variation in a variety of reactions is unequivocally due to the high degree of site-selectivity in the cyclopropane-ring-openings of the three bonds (bonds A, B, and C).
Overview of the recent progress on the chemical studies of antitumor alkaloid, camptothecin (CPT), and its close relatives is described. This article covers 1) isolation and synthesis of possible biosynthetic intermediates of CPT starting from an indole alkaloid, strictosamide, 2) recent total synthesis of racemic and chiral CPT, and 3) a mechanism of anticancer action of CPT using the Topo I-DNA-CPT ternary complex model, which was proposed on the basis of chemical and biochemical information combined with the X-ray crystal structure of the complex of Topo I and DNA, as well as recent medicinal chemistry studies on the development of potent anticancer chemotherapeutics having camptothecinoid structures.
Thermodynamic property of triple helix and the mechanism of inhibition of mRNA transcription by triple helix formation are summarized in this review. I also mention on the artificial DNA bending system in which the antiparallel triple helix motif and synthetic linker consisting of polyether nucleotide units are utilized as the bender. Systematic analysis of this system revealed the anisotropic flexibility of DNA. Thus, DNA seems to be more flexible in minor groove direction as compared to that expected from the classic elastic coil and elastic rod model of duplex DNA.
Computational methods of organic reactions in solution are reviewed. The results of a series of molecular orbital calculations of the Wittig reaction are presented as an example which shows how the molecular orbital calculation is used to analyze the reaction and why computations of solvent effect are required. The theoretical bases of recently developed methods, including the supermolecule method, molecular simulation (Monte Carlo and molecular dynamics methods), QM/MM, RISM-SCF, and dielectric continuum model, are described with the stress on the applicability and limitation of the methods. The calculated results on several reactions such as solvolysis, the Finkelstein reaction and the Menschutkin reaction are presented.
With the increase of interest in the electrooptical devices using ferroelectric liquid crystals, there has been a considerable amount of efforts in the synthesis and evaluation of many compounds exhibiting Sc* phase. Particularly, the wide range of temperature and the low rotational viscosity are needed for the practical use. In order to solve these problems, it is important to design the liquid crystal that has a properly designed size of molecule and a suitable chiral center. It is particularly effective to introduce methylene chain linkage between a chiral carbon atom and core part. We also study the effect of the substitution of fluorine atoms on the benzene ring and the chiral part. We established the method for the synthesis of these kinds of liquid crystals utilizing the enzymatic method in high optical yield.