Ketyls, and

Figure Bl.16.19. (a) CIDEP spectrum observed in die photolysis of xanthone (1.0 x 10 M) in cyclohexanol at room temperature. The stick spectra of the ketyl and cyclohexanol radicals with RPM polarization are presented, (b) CIDEP spectrum after the addition of hydrochloric acid (4.1 vol% HCl 0.50 M) to the solution above. The stick spectra of the ketyl and cyclohexanol radicals with absorptive TM polarization are presented. The bold lines of the stick spectra of the cyclohexanol radical show the broadened lines due to ring motion of the radical. Reprinted from [62].

Benzene is distilled over benzophenone ketyl and stored under a nitrogen atmosphere. 

If the primary chemical process is still abstraction of a hydrogen atom to produce the benzophenone ketyl radical, one would expect to observe some mixed pinacol product arising from coupling of the benzophenone ketyl and acetone ketyl radicals,... 

THF is distilled from benzophenone ketyl and stored over sodium wire under a nitrogen atmosphere. For the drying procedure and caution, see Org. Synth., Coll. Vol. VI11990, 451 and Org. Synth., Coll. Vot. V1973, 976 respectively. 

A. le Berre and P. Goasguen, Autoxidation of metal ketyls and related compounds. Compt. Rend. 254, 1306-1308 (1962). 

Kinetic Parameters of Reduction of Peroxides by Ketyl and Alkyl Radicals [68]... 

Ketyl radicals are more active reducing agents than alkyl radicals. It is seen from the comparison of the rate constants and the activation energies for reactions of ketyl and alkyl radicals with hydrogen peroxide [68],... 

A new entry to exocyclic dienes was reported by Sha who uncovered that a radical cyclization of the vinyl iodide 100 can lead to the formation of an exocyclic dienes fused with a tetrahydrofuran ring. The cyclization is proposed to proceed in a 5-(n-exo)-exo-dig fashion <00OL2011>. 3,4-Disubstituted tetrahydrofurans can also be constructed via the cyclization of O-stannyl ketyls and allylic 0-stannyI ketyls onto electron-rich or electron-poor alkenes <00TL8941>. 

Hoppe D, Marr F, Bruggemann M (2003) Enantioselective Synthesis by Lithiation Adjacent to Oxygen and Electrophile Incorporation. 5 61-138 Hou Z, Wakatsuki Y (1999) Reactions of Ketones with Low-Valent Lanthanides Isolation and Reactivity of Lanthanide Ketyl and Ketone Dianion Complexes. 2 233-253 Hoveyda AH (1998) Catalytic Ring-Closing Metathesis and the Development of Enantioselective Processes. 1 105-132 Huang M, see Wu GG (2004) 6 1-36... 

Given the large number of tandem cyclization processes that have been explored [63], it is disappointing to note that so few have been promoted electrochemi-cally. There appears to be a significant opportunity for additional exploration. Two tyiws of tandem cathodic cyclizations are discussed below. The first involves generation of a ketyl, and its subsequent cyclization onto a pendant alkene to afford a new radical that closes onto a second alkene [64,65]. The second focuses on chemistry not yet discussed involving the reductive cyclization of enol phosphates of 1,3-dicarbonyl compounds [66]. 

In the case of the anion-radical of benzophenone, the effect of an added electron is not very specific It results in weakening of multiple bonds and strengthening of single bonds. Such an effect is usual for all organic anion-radicals. One-electron reduction of benzophenone, a fully conjugated ketone, yields a ketyl and results in the general bond loosening (Scheme 2.38). 

Other transient radicals such as (SCN)2 [78], carbonate radical (COj ) [79], Ag and Ag " [80], and benzophenone ketyl and anion radicals [81] have been observed from room temperature to 400°C in supercritical water. The (SCN)2 radical formation in aqueous solution has been widely taken as a standard and useful dosimeter in pulse radiolysis study [82,83], The lifetime of the (SCN)2 radical is longer than 10 psec at room temperature and becomes shorter with increasing temperature. This dosimeter is not useful anymore at elevated temperatures. The absorption spectrum of the (SCN)2 radical again shows a red shift with increasing temperature, but the degree of the shift is not significant as compared with the case of the hydrated electron. It is known that the (SCN) radical is equilibrated with SCN , and precise dynamic equilibration as a function of temperature has been analyzed to reproduce the observation [78],... 

In the ESR spectra of some related trimethylsilyl benzoquinone derivatives, as with the ketyls, the spin density in the quinone ring increases for trimethylsilyl substitution and decreases for alkyl substitution, consistent with the electron-accepting ability of the trimethylsilyl group. This ability is also manifested in the reduction potentials of the compounds (65). The ESR data for the trimethylsily ketyls and for the trimethylsilyl benzoquinone anion radicals are summarized in Table IX. 

Peroxide-free tetrahydrofuran (THF) (predried first over KOH pellets followed by sodium wire) and 1,2-dimethoxyethane (dme) (predried over sodium wire) are distilled from sodium benzophenone ketyl and stored under purified nitrogen in Schlenk vessels equipped with Teflon Rotaflo or Young taps. 

Alkyllithium-transition metal halide catalysis is completely different from the sodium ketyl and alfin catalysis. Natta, Danusso, Scanesi and Macchi (36) have found that the polymerization of styrene and substituted styrenes by titanium tetrachloride-triethyl aluminum catalysts was different from the above anionic systems. A plot of the log of the rate of the polymerization against Hammett s sigma constant produced a straight line with a rho value of —1.0. Electron releasing groups facilitated this polymerization. 

Transition metal paramagnetic complexes that warrant further comment are the radical anions derived from metallocene- (especially ferrocene-) ketyls and related species, such as compounds IX (61), X (45), or XI (146), and metallonitroxides. From the ESR spectra of compounds... 

Compared with 49, 2,5-dioxabicyclo[2.2.2]octan-3-one (54) prepared from sodium 3,4-dihydro-2//-pyran-2-carboxylate has a much low polymerization reactivity [54] Lewis acids such as antimony pentachloride, phosphorus pentafluoride, and boron trifluoride etherate were not effective at all to initiate the polymerization of 54. Trifluoromethanesulfonic acid induced the polymerization of 54, but the yield and molecular weight of the polymer were low. Bicyclic lactone 54 was allowed to polymerize with anionic and coordination initiators such as butyl-lithium, lithiumbenzophenone ketyl, and tetraisopropyl titanate. However, the... 

Inoue, Tsuruta, and Furukawa (30) found that metal ketyls polymerized acrylonitrile and methyl methacrylate, but not styrene. The lithium ketyls and dilithio complexes were not very active even in tetrahydrofuran. The disodio ketyl complex polymerized styrene quantitatively to give a living system. 

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