Arenes deuteration

The symmetric series provides functional cyclohexadienes, whereas the non-symmetric one serves to build deuterated and/or functional arenes and tentacled compounds. In both series, several oxidation states can be used as precursors and provide different types of activation. The complexes bearing a number of valence, electrons over 18 react primarily by electron-transfer (ET). The ability of the sandwich structure to stabilize several oxidation states [21] also allows us to use them as ET reagents in stoichiometric and catalytic ET processes [18, 21, 22]. The last well-developed type of reactions is the nucleophilic substitution of one or two chlorine atoms in the FeCp+ complexes of mono- and o-dichlorobenzene. This chemistry is at least as rich as with the Cr(CO)3 activating group and more facile since FeCp+ activator is stronger than Cr(CO) 3. 

A palladium-mediated Stille-C-H functionalization process was recently disclosed. Deuteration of the fused arene led to 92% D-incorporation in the vinylsilane product, suggesting a Pd-migration process (Equation (159)).133... 

A very different neutrally charged complex for alkane activation has been reported recently and is shown in Scheme 34(A). The compound is a hydridoplatinum(II) complex bearing an anionic ligand based on the familiar nacnac-type, but with a pendant olefin moiety (97).This complex is extremely soluble in arenes and alkanes and activates C-H bonds in both types of hydrocarbons. This is indicated by deuterium incorporation from deuterated hydrocarbon into the substituents on the arene of the ligand and into the Pt hydride position (A A-d27, Scheme 34). The open site needed for hydrocarbon coordination at Pt(II) is created by olefin insertion instead of anion or solvent substitution (97). 

Substituting deuterium for hydrogen gas in the reduction of BT to DHBT with the catalyst precursor [Rh(NCMe)3(Cp )](BF4)2 has shown that the stereoselective ds-deuteration of the double bond is kinetically controlled by the tj2-C,C coordination of BT. The incorporation of deuterium in the 2- and 3-positions of unreacted substrate and in the 7-position of DHBT has been interpreted in terms of reversible double-bond reduction and arene-ring activation, respectively (Scheme 16.14) [55]. 

Careful studies by C. Eabom have shown that electrophilic aromatic substitution of silicon is faster than substitution of hydrogen. Thus a silicon in an aromatic ring directs substitution with hardly any rearrangement. This technique is particularly useful for preparation of specifically deuterated arenes as protolysis (deuterolysis) or aryl silanes is rapid. 

Relatively simple spectra are obtained from spin adducts of the hindered nitroso-arenes, and these may be further refined by deuteration of the spin trap (Terabe et al., 1973). In spite of being substantially dimerized, even in dilute solution,6 nitrosodurene (ND) has two considerable advantages over MNP. Firstly, it is more reactive towards radical addition (Table 5, p. 33). Secondly, it is not sensitive to visible light, and even on ultraviolet irradiation any photodecomposition is apparently not a major source of nitroxides. 

The difference in the electron affinity between light and heavy isotopic isomers is, in other words, the difference in the stability of their anion-radicals. Such a difference gives a valuable tool for use in probing the chemistry of anion-radicals. The difference in the stability of the ring-deuterated and ring-nondeuterated arene anion-radicals has been employed to examine the transition states for the one-electron-promoted cleavage of naphthyl methyl phenyl ether and naphthyl benzyl ether (Guthrie and Shi 1990). In this reaction, the potassium salt of fluoranthene anion-radical was an electron donor ... 

Steric arguments suggest that the addition of dihydrogen to [Os]-arenes should occur on the arene face opposite that of metal coordination. This theory is supported by the generation of l-d4 upon the partial deuteration of 1. Furthermore, the hydrogenation of complexed anisole (5) under anhydrous conditions yields complexed 3-methoxycyclohexene (6), in which the methoxy group is syn to the metal. It was found, however, a trace of water in the reaction mixture results in the formation of complexed cydohexenone (7), presumably from the attack of water on the dihydroanisole intermediate [13]. 

The tetraallyl complex Th( -C3H5)4 supported on dehydroxylated y-alumina is an outstanding heterogeneous catalyst for arene hydrogenation that rivals the most active platinum metal catalysts in activity. Th() -C3H5)4/DA also catalyzes the rapid and selective deuteration of linear and cyclic alkanes. C-H reactivities fall in the order primary > secondary > tertiary. 

In reduction of arenediazonium fluoroborate with tributylstannane, formation of the arene takes place not only by hydrogen atom abstraction from the stannane, but also by reaction of the radical interm iate with the solvent. Reduction of 4-methoxybenzenediazonium fluoroborate with tributyltin deuteride in te-trahydrofuran or acetonitrile affords not only deuterated but also deuterium-free arenes (equation 89). There are also small amounts of biphenyl by-products. ... 

Deuteration of arenes, 206 Deuterium, role in nmr, 243 Dextrorotatory, 70 Diastereomers, 69 conformational, 80 Diastereoselective reactions, 91 Diazine, 458, 460 Diazomethane, 67, 353 Diazonium ions, 409 Diazonium salts, 416 Dicarboxylic acids, 342 Diels-Alder reaction, 154 Dienes, polymerization, 153j summary of chemistry, 154 Dienophile, 154 Dihalides, dehalogenation, 91 Dimethyl sulfoxide (DMSO), 305 Dioxane, 285 Dioxin, 447... 

The mechanism of aromatization of deuterated and otherwise substituted arene 1,2-oxides to phenolic products has been studied in detail (Figure 13). Pathways leading to phenols A and B correspond to substituent loss, whereas phenols C and D represent substituent migration. Type A phenols are most commonly formed and have been isolated from aromatization of a range of monosubstituted arene 1,2-oxides for example, 33 and 34, 35 and 36, 37, 38, 39, and... 

A tentative structure for 44, incorporating one chemical defect and possessing exchange coupling of a symmetric spin trimer, was proposed.105 It was speculated that the annelation of calix[4]arene-based macrocycles leads to substantial strain, especially in the center macrocycle.105 Such strain could have two consequences (1) increased basicity of the arylmethyl carbanion sites, which would facilitate deuterium abstraction from the deuterated solvent, and (2) increased out-of-plane twisting of the 7r-system, which would weaken the exchange coupling.105... 

Evidence for alkane activation has also been seen by the observation of H/D exchange between two alkanes, an alkane and an arene, or an alkane and THE Using CpRe(PPh3)2H2 as the photo catalyst, thousands of turnovers have been observed. While the intermediate responsible for this catalysis was not identified, it does not appear to be [CpRe(PPh3)H2] undergoing Rem/Rev oxidative addition/reductive elimination, since no deuterium incorporation was observed in the dihydride catalyst [99]. Several other metal hydrides are known to catalyze H/D exchange between alkanes and deuterated benzene, such as Ir(PMe3)2H5 [100],CpMo(dmpe)H3 [101], and Re[P(c-hexyl)3]2H7 [102]. 

PF Fitzpatrick. Kinetic isotope effects on hydroxylation of ring-deuterated phenylalanines by tyrosine hydroxylase provide evidence against partitioning of an arene oxide intermediate. J Am Chem Soc 116 1133—1134, 1994. 

The GaCls-promoted reaction of alkynylsilanes with arenes, fhen treatment wifh MeLi followed by hydrolysis, yields -arylvinylsilanes (Scheme 10.206) [538]. When D2O is added in fhe hydrolysis step, the a-carbon of fhe vinylsilane product is deuterated. This indicates fhe presence of vinylgallium species in fhe reaction mixture. The arylation mechanism probably involves the Friedel-Crafts-type reaction of GaClj-coordinated alkynylsilanes at the -position. 

Fig. 16. The rope jumping motion of the N04 crown of the functionalized calix[4]arene 10 on the coordinated Ag(I) ion. The flip-flop movement results from the fact that the N04 ring has too small an aperture to encompass the metal ion. In a CH2CI2/CH3OH solution (4 1 v/v, deuterated solvents) the oscillating motion slows down with temperature and stops at -20 °C...

Some years ago Cornelisse reported that deuteration of alkyl benzenes results in a deuterium isotope effect upon the quantum yield of the meta photocycloaddition reaction with alkenes. In a new report the same group has published an analysis describing how the observed isotope effect upon the reaction quantvun yield can be ascribed to a kinetic deuterium isotope effect on the excited state reaction and distinguished from an effect upon the unimolecular photophysical modes of decay of the excited state. In addition, it is reported that when the quantum yield of meta photocycloaddition of cyclopentene to alkyl benzenes is measured using a mixture of deuterated and non-deuterated benzenes, the quantum yield is arene concentration dependent.The authors argue that this arises from competition between cycloaddition and the formation of mixed excimers between deuterated and non-deuterated alkyl benzenes which dissociate to yield excited deuterated alkyl benzene and ground state non-deuterated alkyl benzene preferentially. 

Stoichiometric cycloruthenation reactions, as well as the early example of catalytic deuteration of phenol (see above) [38] served for the development of efficient catalytic strategies for C-C bond formations through C-H bond functionalizations. Indeed, ruthenium-catalyzed atom-economical [51] addition reactions of arenes onto C-C multiple bonds, hydroarylations [52-57], were found to be very useful. In an early example, Lewis and Smith disclosed a regioselective alkylation of phenol through in situ formation of its phosphite, and subsequent directed C-H bond functionalization (Scheme 8) [58],... 

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