Recent progress in synthetic chemistry of cyclic ether derivatives has been reviewed. Newly developed methods especially for the stereocontrolled construction of seven- and eight-membered cyclic ether derivatives are described. These include (1) direct cyclization method from alcohols, (2) synthesis from lactones, (3) intramolecular alkylation method, (4) ring enlargement method, (5) reductive synthesis from bicyclic ketals.
In the past several years, metabolites derived from arachidonic acid via the leukotriene (LT) cascade have attracted much interest in the scienticic community because of their biologically important nature. Since LTs are available in minute quantity from biological sources, much efforts have been paid for their chemical synthesis to evaluate their biological properties This review summarizes the recent progress on the chemical synthesis of LTs in their natural form, which includes epoxy LT (LTA4), dihydroxy LT (LTB4 and DiHETE), peptide LT (LTC4-F4), monohydro (pero) xy LT (H (P) ETE), lipoxins, hepoxilins, and trioxilins.
Various kinds of carboxylic acids have been converted to the corresponding sulfides, halides, hydrocarbons, selenides and tellurides, peroxides, and alcohols directly via the radical decarboxylative reactions of the acyl esters (activated esters) of N-hydroxy-2-thiopyridone under the irradiation (tungsten lump) or heating (mainly in benzene) conditions, and further the addition products of the formed decarboxylated alkyl radical to the active olefinic compounds (phenyl vinyl sulfone, nitroethylene, ethyl acrylate etc) have been obtained in good yields. These addition products were further converted to the C1 homologated sulfides, C1 homologated carboxylic acids, aldehydes, ketones, and phosphorus compounds. Finally, the same kinds of radical decarboxylative reactions were applied to, form the corresponding alkoxycarbonyl, alkoxy, and amino radicals starting from alcohols and amines, respectively. Therefore the radical reactions with N-hydroxy-2-thiopyridone are very rich chemistry.
In terms of the efficient and/or unambiguous synthesis of complex peptides (proteins) containing several cystine residues, the existing methods are still less than satisfactory. Therefore one of our research interests has been focused on methodological improvements for the chemical synthesis of cystine peptides. We developed two new disulfide bond forming reactions; the one by thallium (III) oxidation and the other by acid catalyzed reaction involving S-protected cysteine sulfoxides, in addition developed a new S-deprotecting method by using AgOTf. We wish to describe three methods above mentioned and the applications for the syntheses of cystine-containing peptides.
This review summarizes the authors' own works on the use of mesoionic compounds for the preparation of several heterocyclic systems. From six- to ten-membered cyclic conjugated heterocycles have been prepared by the dipolar cycloadditions of mesoionic compounds, and subsequent extrusions and ring expansions of the adducts. Mesoionic compounds react with 7-heteranorbornadiene derivatives to give two aromatic heterocycles by fragmentation of the ylide intermediates resulting from cycloaddition-extrusion. Other reactions covered in-clude [4π + 6π] cycloadditions, preparation of o-quinonoid heterocycles, cycloaddition-extrusion reactions with cumulenes, intramolecular cycloaddition-extrusion reactions, and tandem cycloadditions. Several features of mesoionic compounds as dipolar building blocks of heterocycles are briefly discussed.
The chemical species containing nitrogen-phosphorus double bond are known as the iminophosphorane. We have prepared novel N-vinyliminophosphoranes by the reaction of vinyl azides with tertiary phosphines. The iminophosphoranes underwent enamine type C-C bond formation and following aza-Wittig reaction to give nitrogen heterocycles. The reaction of N-vinyliminophosphoranes with α, β-unsaturated ketones resulted in the formation of pyridines. The reaction was also applicable for the synthesis of [n] (2, 4) pyridinophanes (n=6-9) by using cyclic α, β-unsaturated ketones. In the reaction with α-bromoketones, preparation of pyrrole ring system was accomplished. Furthermore, the reaction with tropone derivatives and fulvene derivatives resulted in the formation of 1-azaazulene and 5-azaazulene ring systems. The chemical properties of these azaazulenes were also studied. These reactions are general and serve as a convenient route for the synthesis of pyridine, pyrrole and azaazulene ring systems.