Dimerization naphthalene

Figure 5 Dimeric naphthalene polyketides from fungi...

Oxidative repair is not a unique feature of our Rh(III) complexes. We also demonstrated efficient long-range repair using a covalently tethered naphthalene diimide intercalator (li /0 1.9 V vs NHE) [151]. An intercalated ethidium derivative was ineffective at dimer repair, consistent with the fact that the reduction potential of Et is significantly below the potential of the dimer. Thymine dimer repair by a series of anthraquinone derivatives was also evaluated [151]. Despite the fact that the excited triplets are of sufficient potential to oxidize the thymine dimer ( 3 -/0 1.9 V vs NHE), the anthraquinone derivatives were unable to effect repair [152]. We attribute the lack of repair by these anthraquinone derivatives to their particularly short-lived singlet states anthraquinone derivatives that do not rapidly interconvert to the excited triplet state are indeed effective at thymine dimer repair [151]. These observations suggest that interaction of the dimer with the singlet state may be essential for repair. 

Attempts to produce dimers of naphthalene similar to those observed for anthracene (Chapter 2) have been unsuccessful, although three naphthalene derivatives have been reported to produce dimer (65) upon photolysis<78) (the structure of these dimers have been the object of some debate, however) ... 

Why these naphthalene derivatives should dimerize while most others are stable to ultraviolet irradiation is unclear. 

As with 2-cyclopentenone, the ratio (70) (71) varies with the molar concentration of the enone, the head-to-head dimer (71) becoming increasingly important at higher concentrations/133 This reaction is efficiently sensitized by acetophenone, benzophenone, thioxanthone, and naphthalene. The same enone concentration effect was observed in the sensitized photo-dimerization as in the direct photolysis. Similarly, quenching of the dimerization by piperylene was not accompanied by a change in dimer ratio. Systematic... 

The naphthalene radical-anion transfers an electron to a monomer such as styrene to form the styryl radical-anion which dimerizes to a dianion... 

Photolysis of acyldisilanes at A > 360 nm (103,104) was shown, based on trapping experiments, to yield both silenes 22 and the isomeric siloxy-carbenes 23, but with polysilylacylsilanes only silenes 24 are formed, as shown by trapping experiments and NMR spectroscopy (104,122-124) (see Scheme 4). These silenes react conventionally with alcohols, 2,3-dimethylbutadiene (with one or two giving some evidence of minor amounts of ene-like products), and in a [2 + 2] manner with phenyl-propyne. Ketones, however, do not react cleanly. Perhaps the most unusual behavior of this family of silenes is their exclusive head-to-head dimerization as described in Section V. More recently it has been found that these silenes undergo thermal [2 + 2] reactions with butadiene itself (with minor amounts of the [2 + 4] adduct) and with styrene and vinyl-naphthalene. Also, it has been found that a dimethylsilylene precursor will... 

The most rapid reaction is N—N-dimerization (the rates of reactions A, B, C are related as 1 0.15 0.02 [94], Naphthylaminyl radicals recombine with the formation of N—C-dimers only [95], probably because voluminous naphthalene rings sterically hinder N—N-dimerization. A correlation between the rate constant of hyperfine splitting on the nitrogen atom of the aminyl radical and the rate constant of recombination of substituted ( (YC6H4)2N ) diphenyl-aminyl radicals was observed [95],... 

Photolytic. Based on data for structurally similar compounds, acenaphthylene may undergo photolysis to yield quinones (U.S. EPA, 1985). In a toluene solution, irradiation of acenaphthylene at various temperatures and concentrations all resulted in the formation of dimers. In water, ozonation products included 1,8-naphthalene dialdehyde, 1,8-naphthalene anhydride, 1,2-epoxyacenaphthylene, and 1-naphthoic acid. In methanol, ozonation products included 1,8-naphthalene dialdehyde, 1,8-naphthalene anhydride, methyl 8-formyl-1-naphthoate, and dimethoxyacetal 1,8-naphthalene dialdehyde (Chen et al., 1979). Acenaphthylene reacts with photochemically produced OH radicals and ozone in the atmosphere. The rate constants and corresponding half-life for the vapor-phase reaction of acenaphthylene with OH radicals (500,000/cm ) at 25 °C are 8.44 x lO " cmVmolecule-sec and 5 h, respectively. The rate constants and corresponding half-life for the vapor-phase reaction of acenaphthylene with ozone at 25 °C are... 

Later in 1965, Chart and Davidson [2] reported the first example of cyclometal-lation of an sp C—H bond in [Ru(dmpe)2] (3) dmpe = dimethyl phosphinoethane. These authors found not only that this complex spontaneously cyclometaUates at the phosphorus methyl groups to produce complex [Ru(H)(CH2P(Me)CH2CH2PM 62)(dmpe)] (4 see Scheme 13.4) (a later examination by Cotton and coworkers [9] of this compound provided crystallographic evidence that the cyclometalated form of [Ru(dmpe)2] is in fact a dimer (5) of the type shown in Scheme 13.3), but also that the system reacts with free naphthalene via the oxidative addition of a C—H bond to the zero-valent rathenium center to produce complex [cis-Ru(H)(2-naphthyl)(dmpe)2] (6). This species was in equilibrium with the r-coordinated naphthalene ruthenium complex [Ru(naphthalene)(dmpe)2] (7) (Scheme 13.4). 

A kinetic study of nitrous acid-catalyzed nitration of naphthalene with an excess of nitric acid in aqueous mixture of sulfuric and acetic acids (Leis et al. 1988) shows a transition from first-order to second-order kinetics with respect to naphthalene. (At this acidity, the rate of reaction through the nitronium ion is too slow to be significant the amount of nitrous acid is sufficient to make one-electron oxidation of naphthalene as the main reaction path.) The reaction that initially had the first-order in respect to naphthalene becomes the second-order reaction. The electron transfer from naphthalene to NO+ has an equilibrium (reversible) character. In excess of the substrate, the equilibrium shifts to the right. A cause of the shift is the stabilization of cation-radical by uncharged naphthalene. The stabilized cation-radical dimer (NaphH)2 is just involved in nitration ... 

Tanaka et al. (1996,2000) studied the behavior of a series of naphthalene derivatives in AN solution containing NaN02 and CF3SO3H at 0°C in air. Naphthalene showed very low reactivity, and most of the starting material was recovered after the reaction. In case of 1-methylnaphthalene, a coupling reaction took place to produce 4,4 -dimethyl-l,T-binaphthyl in 91% yield alongside mononitro derivatives of the dimer in 1.5% yield. However, when the reaction is carried out on the same conditions but in inert (Nj) atmosphere, the yield of the dimer decreased from 97 to 15%, and no mononitro derivatives were formed. Therefore, the oxidation of NO with O2 to form NO2 (after the electron transfer to NO from 1-methylnaphthalene) is an obvious step of the reaction depicted in Scheme 4.42. 

In terms of nitration, the system (NaN02 + CF3SO3H) is of no interest. At the same time, dimerization in this system can be attractive. For the last direction, CF3SO3H (or FSO3H) is necessary to produce binaphthyl derivatives more preferentially than nitro compounds (Tanaka et al. 1996). This work was preceded by the observation that the reaction of NO+AICI4 with 1-methyl-, 1,2-dimethyl-, 1,3-dimethyl, or 1,8-dimethylnaphthalenes in liquid SO2 leads to a partial a,a-dimerization (see Borodkin et al. 1993). Ozeryanskii et al. (1998) published the dimerization of l,8-Af,Af-bis(d imethylamino)naphthalene by the action of NOj in CHCI3. This reaction is accompanied by the formation of 4-nitro-l,8-A,A-bis(dimethylamino)naphthalene. Both gronps of anthors consider cation-radicals of the initial substrates as intermediate species. 

Ethylene and propylene episulfides polymerize in THE at 0-70°C in the presence of sodium naphthalene, and (importantly) the polymer contains no naphthalene residues. The reaction involves one-electron transfer followed by dimerization of the resulting radical to give a dithiolate ion. This ion then polymerizes an episulfide by anionic mechanism (Boileau et al. 1967 Scheme 7.14). 

Analysis of the products by GC showed that there was a significant amount of naphthalene dimer in the mixture so that under the conditions of these experiments, significant crosslinking occurs. The model compound experiments thus show that significant decarboxylation occurs in the presence of the catafyst but that it is accompanied by crosslinking. However, the catafyst may also be effective in the breaking of these crosslinks, and this is under further study. 

A third important reaction of aromatic radical-cations is carbon-carbon bond formation with a further aromatic substrate. This reaction is limited to the oxidation in acetonitrile of substrates with electrondonating substituents. Radical-cations from benzene, naphthalene and anthracene form a-complexes but do not form a a-bonded reaction intermediate. Tlie dimerization reaction has been investigated both by pulse-radiolysis [22] in water and by electrochemical methods [27] in acetoni-... 

The dynamic behavior of various solid organolithium complexes with TMEDA was investigated by variable-temperature and CP/MAS and Li MAS NMR spectroscopies. Detailed analysis of the spectra of the complexes led to proposals of various dynamic processes, such as inversion of the five-membered TMEDA-Li rings and complete rotation of the TMEDA ligands in their complex with the PhLi dimer (81), fast rotation of the ligands in the complex with cyclopentadienyllithium (82) and 180° ring flips in the complex with dilithium naphthalene (83) °. The significance of the structure of lithium naphthalene, dilithium naphthalene and their TMEDA solvation coiMlexes, in the function of naphthalene as catalyst for lithiation reactions, was discussed . ... 

---