Studies in our laboratory on the syntheses of hydroxyazulenes, azulene thiols, polyaminoazulenes, and azulene analogue of carixarene, and on the synthesis, stabilities, and dynamic stereochemistries of extremely stable carbocations containing azulene were reviewed. 2- And 6- hydroxyazulenes were synthesized as stable crystals, which were found to exist as their keto- and enol-forms depend on the solvent used. 1-Hydroxyazulene and 3-hydroxyguaiazulene were synthesized starting from the corresponding benzoyloxyazulenes as extremely unstable compounds, and the latter was found to isomerize to a mixture of its keto form and oxidative dimers. 1-, 2-, and 6-azulene thiols, and 1, 2-diamino- and 1, 2, 3-triaminoazulene derivatives were synthesized as stable compounds. A series of azulene analogues of triphenylmethyl cation; tri (1-azulenyl) methyl, di (1-azulenyl) phenylmethyl, and (1-azulenyl) diphenylmethyl hexafluorophosphates and their various derivatives were synthesized by hydride abstraction of the corresponding methane derivatives with DDQ. Their pKR+values showed that the stabilities of these cations dramatically increase with the number of azulene rings. Tris (3, 6-di-t-butyl-1-azulenyl) methyl cation showed the highest pKR+ value (14.3) ever observed. The dynamic stereochemistries of these cations were also studied based on the temperature-dependent NMR spectra, which were analyzed by a flip mechanism. First example of one-ring flip mechanism was found for these molecular propellers. Extremely stable di- and trications were also synthesized.
Preparation and exploitation of optically pure ketodicyclopentadiene (KDP), carried out by the author's group, is reviewed. Owing to its molecular bias, its α, β-unsaturated ketone functionality, and its facile thermal extrusion of cyclopentadiene, chiral KDP allows stereoselective introduction of both nucleophiles and electrophiles from the convex face and regeneration of the masked double bond to serve itself as a chiral synthon of cyclopentadienone. Potential of KDP has been demonstrated by enantiocontrolled construction of a variety natural products.
Two new radical reactions are reviewed. 1) Skeletal rearrangement via alkoxy radical; a new radical rearrangement, initiated by radical cyclization between ketones and acetylenes followed by β-cleavage of the alkoxy radical and subsequent radical-olefin cyclization was developed. This reaction realized a single-step conversion from cyclohexanone derivatives to bicyclic cyclooctenones and from cyclopentane derivatives to bicyclic cycloheptenenones. The efficiency of the conversion was greatly influenced by the substituents on the ring and on the side chain. Same type of rearrangement was also observed in the radical reaction of epoxydecalin thiocarbonylimidazolides prepared from 1-hydroxymethyl-1, 2, 3, 4, 4a, 5, 6, 7, 8-octahydronaphthalene derivatives. 2) Asymmetric radical cyclization in the presence of Lewis acid : β-diastereoselective radical cyclizations using α, β-unsaturated 8-phenylmenthyl ester as a chiral radical acceptor was developed. Generally, higher diastereoselectivity was observed when bulky Lewis acid was used at low temperature. Co-ordination of the Lewis acid to the carbonyl oxygen fixed the conformation of α, β-unsaturated ester as s-trans and activated the unsaturated ester as a radical acceptor, chiral (2-methylenecyclopentyl) acetate, (2-methylenecyclohexyl) acetate, (2-cyclopentnly) acetate, and (2-cyclohexenyl) acetate were prepared.
The importance of synthesis of chiral pyrethroid insecticides has been increasing with the progress in studies on stereochemistry-activity relationships. The enzyme-catalyzed kinetic resolution, having become one of convenient methods for preparation of chiral compounds, has been applied for the synthesis of pyrethroid intermediates. This article deals with the kinetic resolution of secondary alcohols using lipase-catalyzed enantioselective hydrolysis, and kinetic resolution of carboxylic acids via the esterase-catalyzed hydrolysis or the biotransformation of nitrile. From the viewpoint of practical preparation of chiral pyrethroid intermediates, stereoconversion of less important enantiomers resulted from kinetic resolution is also disclosed in this article.
Various flower colors are in great part due to anthocyanins. Recently, we have elucidated two new mechanisms for blue flower color development on blue cornflower and blue morning glory. The composition of protocyanin, a blue pigment from cornflower, Centaurea cyanus, was determined to consist of six molecules of succinylcyanins (Sucy), six molecules of malonylflavones (Mafl), one ferric ion and one magnesium ion, [Sucy6Mafl6Fe3+Mg2+]. The blue color of protocyanin was due to the LMCT (Ligand to Metal Charge Transfer) interaction between Sucy and Fe3+. The structure of protocyanin was examined by using Al, Mg-protocyanin. The gross structure is much similar to that of commelinin. The pigment of blue morning glory, Ipomoea tricolor, is an triacylated anthocyanin, HBA. We measured the vacuoler pH of the petal of morning glory by using a proton selective micro electrode. The pHv of the petal of purplish red bud was 6.6 and that of blue open flower petal was 7.7. The anhydrobase anion of HBA must be stabilized by intramolecular stacking. We could solve 80 year's problems, one is about cornflower's pigment and the other is the evidence of the pH theory. In both cases hydrophobic interaction followed by formation of supra-molecule is the key of stabilization of anthocyanidin chromophore.
NMR studies employing oligonucleotides regio-selectively labeled with 15N-atom provide valuable information regarding nucleic acid structures, nucleic acids binding with drugs, and nucleotide-protein interactions. The potential utility of the 15N-labeled oligonucleotides has led to considerable interest in the development of synthetic routes to the required 15N-labeled nucleosides. In this paper, the synthetic methods of the labeled nucleosides are summarized.