Benzyl deuteration

Benzyl bromide can be converted into ethylbenzene (731) by the reaction of Me4Sn. The use of HMPA as a solvent is important. Overall inversion of configuration takes place at the chiral center of deuterated benzyl bro-mide[598]. The cyanomethyiation[599] and methoxymethyiation[600] of aromatic rings are carried out by the reaction of cyanomethyltributyltin (732) and methoxymethyltributyltin. 

The efficiency of reduction of benzophenone derivatives is greatly diminished when an ortho alkyl substituent is present because a new photoreaction, intramolecular hydrogen-atom abstraction, then becomes the dominant process. The abstraction takes place from the benzylic position on the adjacent alkyl chain, giving an unstable enol that can revert to the original benzophenone without photoreduction. This process is known as photoenolization Photoenolization can be detected, even though no net transformation of the reactant occurs, by photolysis in deuterated hydroxylic solvents. The proton of the enolic hydroxyl is rapidly exchanged with solvent, so deuterium is introduced at the benzylic position. Deuterium is also introduced if the enol is protonated at the benzylic carbon by solvent ... 

Under certain conditions surface catalytic deuterations can lead to the exchange of benzylic hydrogens. An example in the steroid field is the exchange of the benzylic hydrogens in estrone methyl ether (42) with deuterium in the presence of palladized charcoal." " According to mass spectrometric analysis, the product (43) contains three deuteriums (83 %), which have been assigned to the 6- and 9a-positions on the basis of NMR evidence." " ... 

Quinoxalin-2-ones are in tautomeric equilibrium with 2-hydroxy-quinoxalines, but physical measurements indicate that both in solution and in the solid state they exist as cyclic amides rather than as hydroxy compounds. Thus quinoxalin-2-one and its A -methyl derivative show practically identical ultraviolet absorption and are bases of similar strength. In contrast, the ultraviolet spectra of quinoxalin-2-one and its 0-methyl derivative (2-methoxyquinoxaIine) are dissimilar. The methoxy compound is also a significantly stronger base (Table II). Similar relationships also exist between the ultraviolet absorption and ionization properties of 3-methylquinoxalin-2-one and its N- and 0-methyl derivatives. The infrared spectrum of 3- (p-methoxy-benzyl)quinoxalin-2-one (77) in methylene chloride shows bands at 3375 and 1565 cm" which are absent in the spectrum of the deuterated... 

A salt effect similar to that reported for the deuteration of methyl benzyl sulfoxide (see Section D. 1.1.1.5.) was also shown in this case (Table 2). 

DMSO or other sulfoxides react with trimethylchlorosilanes (TCS) 14 or trimefhylsilyl bromide 16, via 789, to give the Sila-Pummerer product 1275. Rearrangement of 789 and further reaction with TCS 14 affords, with elimination of HMDSO 7 and via 1276 and 1277, methanesulfenyl chloride 1278, which is also accessible by chlorination of dimethyldisulfide, by treatment of DMSO with Me2SiCl2 48, with formation of silicon oil 56, or by reaction of DMSO with oxalyl chloride, whereupon CO and CO2 is evolved (cf also Section 8.2.2). On heating equimolar amounts of primary or secondary alcohols with DMSO and TCS 14 in benzene, formaldehyde acetals are formed in 76-96% yield [67]. Thus reaction of -butanol with DMSO and TCS 14 gives, via intermediate 1275 and the mixed acetal 1279, formaldehyde di-n-butyl acetal 1280 in 81% yield and methyl mercaptan (Scheme 8.26). Most importantly, use of DMSO-Dg furnishes acetals in which the 0,0 -methylene group is deuter-ated. Benzyl alcohol, however, affords, under these reaction conditions, 93% diben-zyl ether 1817 and no acetal [67]. 

Benzyl radical, C6H5CH2, and its deuterated analogues (C6H5CD2, CfiDsCHz) were obtained by vacuum thermolysis of dibenzyl derivatives or by pyrolysis of the corresponding benzyl bromides (17) (Baskir, 1989). 

Figure 25. X-Band EPR spectra of electrochemically generated [Com(L BuMel )(Ph2acac)]2+ (top) and its at the benzylic methylene deuterated analogue (bottom) the hyperfine coupling constants are given in millitesla (mT). [Adapted from (152).]...

The benzylic compound (1.5 mmol) and TBA-HS04 orTEBA-CI (0.3 mmol) in PhH or CH2Cl2 (1.5 ml) are stirred at room temperature under Ar with a paste of NaOD in D,0 (60-63% w/w, 2 l molar ratio for each hydrogen to be exchanged). On completion of the reaction, the mixture is extracted with CH,Cl2 (3 x 20 ml) and the extracts are washed with H20 (10 ml), dried (MgS04), and evaporated to yield the deuterated product. 

Durst and co-workers (309) investigated in detail the stereochemistry of deuteration and methylation of carbanions derived from optically active (+)-(5)-benzyl methyl sulfoxide 34 and (+)-(i )-benzyl t-butyl sulfoxide 290. The reactions, which allowed the extent of asymmetric induction on the a-carbon atom as well as the stereochemistry of deuteration and methylation to be determined, are summarized in Schemes 30 and 31. 

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 ... 

Reduction of (S)-pinanediol [phenyl(chloro)methyl]boronate with commercially available lithium triethylborodeuteride yields a chirally deuterated benzylboronic ester. Deboronation of the deuterated benzylboronic ester with hydrogen peroxide yields chirally deuterated benzyl alcohol in 96-98% ee70. The conversion of the deuterated benzylboronic ester to chirally deuterated phenylalanine has also been accomplished (Section 1.1.2.1.4.2.). 

In order to determine intrinsic isotope effects of benzylic hydroxylations, the metabolism of different deuterated toluenes was investigated in detail with rat liver microsomes and compared with the chemical radical chlorination of... 

In the deuterated 9-methylffuorenyl system (46), Cram and co-workers found retention of configuration in tetrahydrofuran with ammonia or a primary amine as base.127 Streitwieser has obtained similar results with benzyl systems in cyclohexylamine with cyclohexylamide as base.128 Cram s proposed mechanism is shown in Scheme 6. In dimethylsulfoxide, the exchange and racemization... 

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