Fluorine has received great attention in all fields of science. “Small atom with a big ego” was the title of the Symposium at the ACS meeting in San Francisco in 2000, where a number of the current scientific and industrial aspects of fluorine chemistry made possible by the small size and high electronegativity of the atom were discussed. This small atom has provided mankind with significant benefits in special products such as poly(tetrafluroethylene) (PTFE), freon, fluoro-liquid crystals, optical fiber, pharmaceutical and agrochemical compounds, and so on, all of which have their own unique properties that are otherwise difficult to obtain.1 For instance, at present, up to 30% of agrochemicals and 10% of pharmaceuticals currently used contain fluorine atoms. Therefore, organic fluorine compounds have received a great deal of interest and attention from the scientists involved in diverse fields of science and technology. Now, not only C-F bond formation but also selective C-F bond activation have become current subjects of active investigation from the viewpoint of effective synthesis of fluoroorganic compounds. The former is highlighted by designing a sophisticated fluorinating reagent for regioand stereocontrolled fluorination and developing versatile multifunctional and easily prepared building blocks. C-F bond formation has been treated extensively in several reviews2 and books.3 The latter is a subject that has been less explored but would be promising for selective defluorination of aliphatic fluorides, cross-coupling with aryl fluorides, and * To whom correspondence should be addressed. Phone: 81-78-803-5799. Fax: 81-78-803-5799. E-mail: amii@kobe-u.ac.jp and uneyamak@cc.okayamau.ac.jp. † Kobe University. ‡ Okayama University. Chem. Rev. 2009, 109, 2119–2183 2119

C-F bond activation in organic synthesis.

Nucleophilic substitution reactions by electron transfer

Pterin-Dependent Amino Acid Hydroxylases.

Soluble methane monooxygenase (sMMO) catalyzes the oxidation of methane to methanol. Single-turnover reactions of sMMO from Methylococcus capsulatus (Bath) were studied by stopped-flow optical spectroscopy to examine further the activated dioxygen intermediates and their reactions with hydrocarbon substrates. A diiron(III) peroxo species designated H{sub peroxo} is the first intermediate observed in the reaction between the chemically reduced hydroxylase (H{sub red}) and dioxygen. The optical spectrum of this species determined by diode array detection is presented for the first time and exhibits visible absorption bands with {lambda}{sub max} {approx} 420 nm ({epsilon} = 4,000 M{sup {minus}1} cm{sup {minus}1}) and {lambda}{sub max} = 725 nm ({epsilon} = 1,800 M{sup {minus}1} cm{sup {minus}1}). The temperature dependences of the rate constants for formation and decay of H{sub peroxo} and for the subsequent intermediate, Q, were examined in the absence and in the presence of hydrocarbon substrates, and activation parameters for these reactions were determined. For single-turnover reaction kinetics monitored at 420 nm, the {lambda}{sub max} for Q, a nonlinear Eyring plot was obtained when acetylene or methane was present in sufficiently high concentration. This behavior reflects a two-step mechanism, Q formation followed by Q decay, in which the rate-determining step changes depending on themore » temperature. The rate of H{sub peroxo} formation does not depend on dioxygen concentration, indicating that an effectively irreversible step involving dioxygen precedes formation of the diiron(III) peroxo species. The rate constant observed at 4 C for H{sub peroxo} formation, 1--2 s{sup {minus}1}, is slower than that determined previously by Moessbauer and optical spectroscopy, {approximately}20--25 s{sup {minus}1} (Liu, K. E., et al. J. Am. Chem. Soc. 1995, 117, 4997--4998; 10174--10185). Possible explanations for this discrepancy include the existence of two distinct peroxo species. Intermediate Q exhibits photosensitivity when monitored by diode array methodology, a property that may arise from enhanced reactivity of a transient charge-transfer species. The photoreaction can be avoided by using a monochromator to obtain kinetics data at single wavelengths. The reactions of substrates with intermediate species were studied by single- and double-mixing stopped-flow spectroscopy. The Q decay rate exhibits an approximate first-order dependence on substrate concentration for a wide range of hydrocarbons, the relative reactivity varying according to the sequence acetylene > ethylene > ethane > methane > propylene > propane. In addition, the data indicate that H{sub peroxo} can oxidize olefins but not acetylene or saturated hydrocarbons.« less

Mechanistic studies of the reaction of reduced methane monooxygenase hydroxylase with dioxygen and substrates

Publisher Summary This chapter discusses single electron transfer and nucleophilic substitution. The SRNl reaction appears as a reaction in which single electron transfer plays a pre-eminent role but is by no means a single elementary step. A different problem is that of the possible involvement of single electron transfer in reactions that are not catalyzed by electron injection (or removal). A typical example of such processes is another substitution reaction—namely, the SN2 reaction. The chapter discusses the reactions in which electron transfer is associated with the breaking of a bond but in which either no bond formation occurs or, if it does, it takes place in aseparated step. There are a number of cases where “true” SN2 mechanisms (in which the bond-breaking and bond-formation steps are concerted) do occur, even with nucleophiles that are members of reversible one-electron reversible redox couples.

Single electron transfer and nucleophilic substitution

2-Isopropylidenecyclopentane-1,3-diyl. Preparation, properties, and reactions of a distorted trimethylenemethane. Direct evidence for a triplet reaction

Product ratios dependent on and independent of the left group in a single series: potassium metal-provoked reactions of aryl halides with amide and acetone enolate ions that occur during mixing

Michael Tremelling

Papers

2-Isopropylidenecyclopentane-1,3-diyl. Preparation, properties, and reactions of a distorted trimethylenemethane. Direct evidence for a triplet reaction

Product ratios dependent on and independent of the left group in a single series: potassium metal-provoked reactions of aryl halides with amide and acetone enolate ions that occur during mixing

2-isopropyliden-cyclopentandiyl-(1,3), darst., eigenschaften und rk. eines deformierten trimethylenmethans, direkter nachweis einer triplett-rk.