Water-soluble novel cyan and magenta dyes, which show high light-fastness and ozone-fastness on porous photo media, have been invented for ink jet printing system. Control of dye energy levels, removal of sensitive groups towards ozone, and acceleration of copper-phthalocyanine complex (CuPc) aggregation were the dominant factors to improve both ozone-fastness and light-fastness significantly. For the development of the CuPc cyan skeleton, alkyl sulfonyl groups, all of which were located at beta positions on the CuPc skeleton, were effective to improve fastness. For the development of the magenta skeleton, the combination of aniline-substituted pyridine coupling component and pyrazole diazonium component was inherently important skeleton to improve fastness. Regarding the production process of the novel CuPc dye, solvent effect, control of pH and dehydration reagent such as an orthoester were the dominant parameters to improve cyclization yield. In the novel magenta dye, both introduction of plural functional groups at the same time and development of a highly regioselective reaction for sulfonation were key synthetic processes to establish a successful synthetic route.
The intramolecular oxy-carbonylation of terminal acetylenes is considered to be a useful method for the conversion of an acetylene unit to a β-ketoester unit utilizing neighboring group participation. The first examples of an asymmetric version of this reaction have been achieved, using some new chiral bis-oxazoline (box) ligands. To demonstrate the utility of this reaction, the chiral total synthesis of (+)-bakkenolide-A was achieved. The box ligand plays an important role in the intramolecular oxy-carbonylation of propargyl acetate having an extra terminal acetylene. In the absence of the box ligand, the second triple bond did not react, affording a cyclic orthoester. The use of the box ligand changed the course of the reaction significantly, yielding either 4-cyclopentene-1,3-dione or a bicyclic lactone by tandem carbonylative cyclization as a result of the reaction (insertion or methoxy-palladation) of the second triple bond.
Methodologies with chiral enolates including the stereoselective construction of the quaternary carbon, rearrangement of the vinylketene N,O-acetals, the remote stereoinduction with vinylketene silyl N,O-acetals, and the construction of 1,2-diols having the tertiary alcohol have been developed to apply to the natural product synthesis. Each isomer at the quaternary carbon has been synthesized from one enantiomer of α,β-unsaturated imide by choosing whether alkylation of the dienolate anion or rearrangement of the vinylketene N,O-acetal with MeAlCl2. The vinylketene silyl N,O-acetals possessing the chiral auxiliary reacted with aldehydes in the presence of TiCl4 to realize the stereocontrol at the γ and δ positions. Aldol reactions with lactate having the chiral auxiliary provided the 1,2-diols possessing the tertiary alcohol. The major stereoisomer depended on the chiral auxiliary and the protective group on the hydroxy group of lactate. These methodologies realized the short-step syntheses of natural products.
Buckybowls, bowl-shaped π-conjugated aromatic hydrocarbons corresponding to partial structures of fullerenes or cap structures of carbon nanotubes, possess the interesting chemical and physical properties due to the unique curved aromatic surfaces. Development of efficient methodology to construct the highly strained bowl-shaped aromatic skeleton has been one of the most challenging and important issues in this field after the discovery of the related fullerenes. The synthetic works on buckybowls have been recently grown drastically since the efficient synthetic methodologies in both solution phase and gas phase (flash vacuum pyrolysis) have been developed in the last 15 years. This review summarizes the synthetic methodologies for the construction of the buckybowl skeletons and the reported buckybowls are presented.
The first asymmetric total synthesis of reveromycin A (1), a potent inhibitor of isoleucyl tRNA synthetase, has been accomplished based on the stereocontrolled construction of the 6,6-spiroketal system, efficient succinylation of the tert-alcohol under high pressure as a key step. The stereocontrolled total synthesis of (−)-spirofungin A (5) and (+)-spirofungin B (6a), polyketide-type antibiotics having various antifungal activities, has been achieved employing the Weinreb amide, the alkyne and the vinyl boronate readily available from the common intermediate employing Horner-Emmons reaction and Suzuki coupling reaction for the construction of the both side chains. The succinates of the tertiary hydroxyl group having the formyl group in the structures were conveniently synthesized by oxidative cleavage of the dihydropyrans prepared from the lactone via coupling of the ketene acetal triflates and zinc homoenolate. Various derivatives of 1, 5 and 6a were synthesized and their inhibitory effects on both the isoleucyl-tRNA synthetase activity and the survival of osteoclasts, and activities on the morphological reversion of srcts-NRK cells were examined.
Recent advances in the field of organocatalytic asymmetric synthesis have provided several new methods for preparing chiral compounds in an environment-friendly manner. Among them, proline-catalyzed asymmetric aldol reactions gather a considerable attention from synthetic chemists. In our recent work on the synthesis of (5R,6S)-(−)-6-acetoxy-5-hexadecanolide, we found that aldehydes bearing a 1,3-dithiane moiety at the β-position could serve as a useful synthon of straight-chain aliphatic aldehydes. This method has been successfully applied to the enantioselective synthesis of biologically interesting natural products such as (+)-boronolide, D-ribo-C18-phytosphingosine, pachastrissamine, and (+)-prosophylline.
The asymmetric ring opening of meso-epoxides with variety of nucleophiles is an important transformation to produce 1,2-bifunctionalized systems and to establish two contiguous stereogenic centers in a single event. This mini-review focuses on the recent advances in asymmetric ring opening of meso-epoxides with halogen-containing nucleophiles to afford the vicinal halohydrins. The vicinal halohydrins can be utilized for some useful synthetic transformations, and are also key imtermediates in the synthesis of natural products.