Photoinduced reactions—LXXI: Photorearrangement of 3-hydroxyflavones to 3-aryl-3-hydroxy-1,2-indandiones

3-Hydroxyflavones (1) were found to undergo a novel photorearrangement to 3-aryl-3-hydroxy-1,2-indandiones (2) which were characterized as o-phenylenediamine adducts, 1-aryl-1-hydroxy-11H-indeno[1,2-b]quinoxalines (3). To the contrary, 3-methoxyflavone underwent photochemical intramolecular hydrogen transfer. Photochemical reactivities of several other flavonoids were examined. It appears that the 5-hydroxyl H-bonded to the 4-carbonyl causes photoresistance in flavonoids.     

Multi-step application of immobilized reagents and scavengers: a total synthesis of epothilone C

The total synthesis of the cytotoxic antitumour natural product epothilone C has provided a stage for the exploitation and further development of immobilized reagent methods. A stereoselective convergent synthetic strategy was applied, incorporating polymer-supported reagents, catalysts, scavengers and catch-and-release techniques to avoid frequent aqueous work-up and chromatographic purification.     

Functional monomers and polymers. LIX. Properties and function of Cu(II) complexes of the copolymers having pendant sulfide and imidazolyl groups

The Cu(II) complexes of copolymers having pendant sulfide and imidazolyl groups were prepared by a free radical copolymerization of ethylvinylsulfide with vinylimidazole, and their properties and function were studied spectrophotometrically in comparison with those of poly[4(5)-vinylimidazole]. The complexes were found to be effective as catalysts for the oxidation of hydroquinone. Visible and ESR spectra of the Cu(II)-copolymer complexes were similar to those of the Cu(II)-homopolymer complexes, while the catalytic activity for the oxidation was different between these complex systems. A rapid reaction followed by a slow reaction, particularly at high ethylvinylsulfide content in the copolymers, was observed in the Cu(II)-copolymer complex systems, but a continuous reaction proportional to the reaction time was observed in the Cu(II)-homopolymer complex systems. The reoxidation rate of Cu(I) to Cu(II) complex, which was little affected by the concentration of imidazolyl group, decreased with a rise of the ethylvinylsulfide content in the copolymer. It was suggested that the sulfur atom of the sulfide group was weakly coordinated to Cu(II) but strongly to Cu(I), and an electron transfer reaction from substrate to the Cu(II) complex was increased, while reoxidation reaction of the Cu(I) complex was decreased in the copolymer complex systems.     

Functional monomers and polymers. CXXXII. Template polymerization of methacrylamide derivatives containing nucleic acid bases

Free-radical polymerizations of methacrylamide derivatives containing nucleic acid bases were studied in the presence of the polymethacrylamide having complementary nucleic acid bases as template polymers. The rate of the polymerization did not show remarkable difference in the presence or the absence of the template polymer. A stable polymer complex, however, was precipitated from the polymerization system, and was found to be different in a thermal analysis from the polymer complex which was obtained by mixing of the complementary polymers in solution. Free-radical copolymerizations in the presence of the template polymers also supported the template polymerization.     

Selective synthesis of allylated oxime ethers and nitrones based on palladium-catalyzed allylic substitution of oximes

[reaction: see text] The viability of oximes as nucleophiles in transition-metal-catalyzed allylic substitution was examined. The oxygen atom of oxime acted as a reactive nucleophile in the reaction of a pi-allyl palladium complex. In the presence of Pd(PPh3)4, the allylic substitution of oximes with allylic carbonate afforded the linear O-allylated oxime ethers selectively without a base. In contrast, the palladium-catalyzed reaction with allylic acetate proceeded smoothly in the presence of K2CO3 or Et2Zn as a base. Selective formation of nitrones was achieved by using palladium(II) catalyst. In the presence of Pd(cod)Cl2, the allylic substitution of oximes with allylic acetate afforded the N-allylated nitrones under solvent-free conditions, as a result of the reaction with the nitrogen atom of oximes.     

Functional monomers and polymers. XXXXI. Template polymerization of methacryloyl-type monomers containing nucleic acid bases

In due consideration of the specific base–base interaction that exists between nucleic acid molecules, the free radical polymerization of N-β-methacryloyloxyethyl derivatives of adenine, thymine, and theophylline initiated by azobisisobutyronitrile (AIBN) was studied in the presence of N-β-methacryloyloxyethyl-type polymers which have complementary nucleic acid bases as template polymers. The rate of polymerization of N-β-methacryloyloxyethyladenine was accelerated when poly(N-β-methacryloyloxyethyluracil) or -thymine was present in the polymerization system. The effect of the stereoregularity of the template polymers, as well as polymerization temperature and the sort of solvents used on the rate of polymerization, was studied and discussed in some detail. The results suggest that the interaction between complementary bases plays a role in template polymerization behavior.     

Enantioselective aza-Henry reaction catalyzed by a bifunctional organocatalyst

[reaction: see text] The aza-Henry reaction of imines with nitroalkanes was promoted by chiral thiourea with an N,N-dimethylamino group to give beta-nitroamines with good enantioselectivity. Various N-protected imines were examined as substrates. N-Phosphinoylimine gave the best result in terms of chemical yield and enantioselectivity (up to 91% yield, up to 76% ee).     

Pd-catalyzed asymmetric allylic alkylation of glycine imino ester using a chiral phase-transfer catalyst

Pd-catalyzed asymmetric allylic alkylation of the glycine imino ester 1a has been developed using a chiral quaternary ammonium salt 3d without chiral phosphine ligands. The proper choice of the achiral Pd ligand, P(OPh)3, is important to achieve high enantioselectivity. By this method with the dual catalysts, numerous enantiomerically enriched alpha-allylic amino acids 4a-h could be prepared with comparable to higher enantioselectivity than that of the conventional asymmetric alkylation of 1a. In addition, the Pd-catalyzed reaction of 1a with 1-phenyl-2-propenyl acetate 2i afforded the branch product 6 with high enantio- and diastereoselectivity (>95% de, 85% ee).     

Functional monomers and polymers. XCVI. Photochemical reactions on oligo- and polyethyleneimines which contain pendant thymine bases

The photodimerization reaction of oligo- and polyethyleneimine derivatives which contain pendant thymine bases in various amounts was studied in aqueous solution in a wide pH range and in N, N-dimethylformamide solution. The photodimerization reaction of these derivatives in poly(methyl methacrylate) was also studied. It was found that its quantum efficiency tended to increase as thymine units were added to the oligomers and copolymers. This result is discussed in terms of the effect of the nearest neighboring thymine units and singlet energy migration, particularly in the polymers.     

Functional monomers and polymers. XXXXVII. Complex formation of stereoregular methacryloyl-type polymers containing nucleic acid bases

The complex formation between a poly(N-β-methacryloyloxyethyl) derivative of adenine with one of thymine or uracil was studied in dimethyl sulfoxide and ethylene glycol mixture by ultraviolet (UV) spectroscopy. For the polymer pairs containing complementary nucleic acid bases both hypochromicity and hyperchromicity were found. Stereoregularity of the polymers, as well as the conditions for measurement of, for example, solvent, temperature, and time, affected the complex formation. Both inter- and intramolecular interaction of polymers in solution were discussed in some detail.