The purpose of the present research is to establish new methods in the commercial production of cyclopentenones. Cyclopentenones are very important compounds for fine chemical industry. (agrochemicals, perfumes, pharmaceuticals) The present paper is concerned with syntheses of cyclopentenones through a molecular rearrangement of 2-furylcalbinols, which was discovered by G. Piancatelli. On this reaction, several improvements are achieved from the industrial viewpoints. This method is applied for the syntheses of following compounds. (1) intermediates of pyrethroidal insecticides (2) optical active cyclopentenones (3) jasmones (4)intermediates of prostagrandins (5) norbornadienes …… compounds for the storage of light energy
In dealing with substituent effects in chemical reactions, only two factors are usually taken into account. They are the polar effect pertaining to charge distribution and the steric effect pertaining to bulk distribution. One more factor must be considered, that is, the ponderal effect pertaining to mass distribution within the molecule under consideration. The ponderal effect is discussed in detail for the Finkelstein exchange, Y-+RX→YR+X- (X, Y=isotopically or chemically different halogens ; R=Me, Et, n-Pr, i-Pr, t-Bu, i-Bu, neoPe), and in brief for a few more reactions. Nonpotential energy effects, including ponderal, may be of particular importance in both surface and enzymatic catalyses. In these catalyses the substrate adsorbs on the catalyst surface or coordinates to the enzyme, resulting in the loss of translational and rotational freedoms. This loss may give rise to quite a large ponderal entropy effect.
This account describes the CD exciton chirality method which is useful for determination of absolute stereochemistry of various natural and synthetic chiral compounds. Chiral exciton coupling between two or more chromophores gives rise to two split CD Cotton effects of opposite signs to each other, from the signs of which absolute configuration of chiral compounds is nonempirically determined, if the direction of transition moments in interacting chromophores is known. The absolute stereochemistries determined by the present method are naturally in accrod with those from the X-ray crystallographic Bijvoet studies. Applications of this versatile chiroptical method to various organic compounds are exemplified ; in Part I, CD Cotton effects due to the exciton interaction between two or more identical chromophores are discussed.
The recent progress of asymmetric synthesis with organo-sulfur compounds involving chiral or achiral sulfur atoms, is reviewed. The asymmetric synthetic methods are classified into the type of structure of the organo-sulfur reagents used ; sulfoxides, sulfinic esters, sulfinarnides, sulfoximines, sulfur ylides, sulfenamides, thiols, sulfides, sulfones, and heterocyclic compounds involving sulfur atoms. At the most part, asymmetric syntheses using readily available chiral organo-sulfur compounds such as sulfoxides as chiral sources are described, classified into the type of reactions ; addition of α-sulfinylcarbanions to carbonyl groups of ketones or aldehydes, addition to imines and nitriles, Michael additions, and rearrangements.
Withanolide, a group of naturally occuring C28 steroidal lactone isolated from the plants of Solanaceae family, has been paid attention for their biological activity, e. g. antitumor and insect antifeedant. The syntheses of jaborosalactones, withaferin A and other several withanolides were achieved. The key steps in the synthesis involve introduction of the desired substituent at C-25 and stereoselective construction of the A/B rings by a facile allyl sulfoxide-sulfenate rearrangement. The biological activities and neighbouring group effects of the A/B ring are also described.
A variety of 3, 4-dihydroisocoumarins (3, 4-DHI) naturally occur as constituents of plant or as metabolites of fungus or bacteria. Most of them have been found to have various important biological activities. This article summerizes our study on the syntheses, reactions, and biological activities of 3, 4-DHI and isochromans along with a review of recent progress in this field.
In this paper, syntheses and characterizations of polymers containing CH=N bond in main chain (polyimine) will be described. Polyimines could be synthesized by the condensation of primary diamines and dialdehydes. The polymers were prepared first by Krässig and Greber in 1953. However, numerous polymerization techniques (solution, melt, Schiff-base exchange and others) and conditions tried have not given high molecular weight polyimines because of the insolubility and the high melting point. But, the discovery of m-cresol method by Suematsu and solid state polymerization by Morgan made high molecular weight polyimine formation possible. m-Cresol accelerated CH=N bond formation keeping a homogeneous solution. The reaction rate in m-cresol was as fast as that of acid chloride and primary amine in benzene, though top limit of degree of polymerization was not very high because of the presence of an equilibrium between polymerization and depolymerization. However, exclusion of reaction-water produced higher molecular weight polymers. The reaction rate in m-cresol was found to obey the reversible second order equation, defined as v=k [CHO] [NH2] -k* [C=N] [H2O], where k is the rate constant in polymerization and k* in depolymerization. The condensation in dilute solution resulted in the formation of macrocyclic imines in high yield. This could be explained not in terms of cyclization theory by Stockmayer et al., but favourable conformational changes and an equilibrium shift accompanied by the separation of products. Chain length of most aromatic polyimines is calculated according to the equation Pn=1/2 [3.6 (AυC=N/AυC=O) +1], where AυC=N and AυC=O are the absorbance of υC=N and υC=O respectively. An equation [η] =1.9×10-3M1.20 by Millaud holds in poly- (p-xylidene-2-methyl-p-phenylenediamine).