A series of highly cross-linked copolymers which retain the selective “memory” for their origins used as templates and are able to control subsequent chemical reactions including rebindings and transformations in a specific stereochemical direction are extensively surveyed from synthetic points of view.
The formation of O- radical over various metal oxides, its reactivity, and catalytic oxidations using O- as an oxidant have been described. It is confirmed by ESR, XPS, TPD etc. that O- radical can be generated through decomposition or charge transfer processes of O2, O2-, OH-, or N2O. Respective characters of O- on various metal oxides, that is, g-values of ESR spectra and desorption temperatures etc., were summarized. Among oxygen species such as O-, O-2 and O-3, O- radical shows the highest activity for stoichiometric oxidations of hydrocarbons and the order of reactivities has been clarified to be O->O-3>O-2 independent of metal oxides. Reaction schemes of O- radical with hydrocarbons have been proposed on the basis of the ESR, IR, and TPD observations and also been compared with those of O-2 and O-3. In the last section, catalytic oxidations of hydrocarbons by nitrous oxide, which decomposes readily and selectively to yield an O- radical on metal oxide surfaces, have been outlined, including new types of catalytic oxidations such as one-step conversions of methane into methanol, of alkanes into alkenes, and of benzene into phenol.
Nonenzymatic synthesis of oligonucleotides by model reactions of nucleic acid biosynthesis is reviewed. The nucleic acid biosyntheis catalyzed by polymerase is described briefly at first. Oligonucleotides are prepared from activated nucleotides catalyzed by metal ions such as Pb2+ and Zn2+ which mimic the role of the metal ion at the active cite of the polymerase. Template-directed synthesis of oligonucleotides is described as a model reaction of nucleic acid replication. The metal ions, the template and the activated nucleotide used as a monomer affect the yield, chain length and regioselecivitv of the resulting oligonucletide.
The molecular recognition of DNA by small molecules including bisintercalators has been described. Site-specific chemical reactions of DNA are next reviewed. These include i) reactions of DNA with oxygen-dependent antibiotics such as bleomycin, neocarzinostatin and camptothecin, and ii) single strand cleavage induced by artificial compound-metal-O2 systems. Sequence specific photoreaction between DNA and psoralenes is briefly discussed. A new method for selective removal of thymine from DNA utilizing photochemical reaction is also described in detail.
Recent publications on the applications of bis (η-cyclopentadienyptitanium compounds in organic synthesis were reviewed according to the following items : 1) Titanium-mediated methylene-transfer reactions. 2) Carbotitanation of acetylenes. 3) η-Allyl titanium compounds in organic synthesis. 4) Hydroalumination of olefins catalyzed by Cp2TiCl2. 5) Titanium-catalyzed olefin metathesis. 6) Cp2TiCl2-catalyzed Grignard reactions.
Recent progress in the chemistry of arenediazonium salts are reviewed and discussed from a viewpoint of their synthetic applications. The reactions described in the article are as follows : a) cyclization reactions in which the diazonium nitrogen is lost or retained ; b) reactions with nucleophiles at the terminal nitrogen ; c) replacements of diazonio group by hydrogen, halogens, hydroxyl, and other groups ; d) arylation reactions which involve Gomberg-Bachmann and Meerwein types of the reaction.