Of benzylic substrates

The reaction is even more general and applicable to ketones bearing an a-methylene. Yields up to 90% of the corresponding dimethyl esters are obtained in the case of benzylic substrates (Scheme 4.19). 

These systems are also described as normal copper proteins due to their conventional ESR features. In the oxidized state, their color is light blue (almost undetectable) due to weak d-d transitions of the single Cu ion. The coordination sphere around Cu, which has either square planar or distorted tetrahedral geometry, contains four ligands with N and/or 0 donor atoms [ 12, 22]. Representative examples of proteins with this active site structure (see Fig. 1) and their respective catalytic function include galactose oxidase (1) (oxidation of primary alcohols) [23,24], phenylalanine hydroxylase (hydroxy-lation of aromatic substrates) [25,26], dopamine- 6-hydroxylase (C-Hbond activation of benzylic substrates) [27] and CuZn superoxide dismutase (disproportionation of 02 superoxide anion) [28,29]. 

Finally, side-chain functionalization may be obtained through a PET process. Apart from the several arylations discussed in Sect. 2.1.3, oxygenation of benzyl radicals obtained from deprotonation or carbon-carbon bond cleavage is preparatively useful (the method has been recently reviewed [254]), and other functionalization are possible, notably fluorination of benzyl substrates by irradiation in the presence of titanium dioxide and fluoride ions [255], Furthermore, the modification of a substituent, as a typical example the reduction of a nitro group [18, 27, 256-259] or an azo group [266], is in some cases obtained through a PET process. 

Cunninghamella elegans has shown a degree of generality in the oxidation of benzylic substrates. For example the tetrahydroquinoline (88) is converted to the derivative (89 equation 30), but the degree of enantioselectivity is not known." Similarly triprolidine (90) is converted to the alcohol (91 equation 31) in respectable yield. 

Albini, A., Fagnoni, M., Photoinduced CX Cleavage of Benzylic Substrates. In Griesbeck, A. G., Mattay, J. (eds), Synthetic Organic Photochemistry, Marcel Dekker, New York, 2005, pp. 453 494. 

Another suggestion is that secondary a-deuterium KIEs can be used to determine the symmetry of an SN2 transition state.55 An examination of the secondary a-deuterium KIEs for several SN2 reactions of benzyl substrates (Table 9) showed there were two different substituent effects on these KIEs. In some SN2 reactions, the KIEs decrease markedly when a more electron-withdrawing substituent is... 

To avoid oversimplification, we note that changes in m values can occur independently of changes in l values when charge delocalization occurs either within the carbocation [e.g., solvolyses of benzyl substrates (3, 65, 66)] or within the anionic leaving group [e.g., solvolyses of picrates (58)]. (It has recently been shown (74) that solvolyses of benzyl tosylate do fit equation 12 satisfactorily.) Such effects appear to be general electrostatic as opposed to specific electrophilic or nucleophilic. These effects can be observed in a... 

H-)-Camptothecin was isolated from Chinese tree by Wall and colleagues in 1966 its potent antitumor property has attracted interest from synthetic chemists. In 1997 Murata, Sakamoto and their team reported a methodology for the functionalization of heteroaromatics, and also applied it in the total synthesis of camptothecin [57]. Palladium-catalyzed carbonylation of benzylic substrates was... 

This reaction is only plausible if phosphide complex 73 is the most nucleophilic species present in the mixture. Therefore, the base must not be too strong to deprotonate 72, otherwise the generated phosphide anion would quiekly react with the benzyl halide to give racemic 74. Sodium trimethylsilanoate appeared to be a good choice. When benzyl bromide was used as the electrophile in the presence of 5% of 73, the tertiary phosphine 74 was obtained in quantitative yield and with 77% ee. Interestingly, with benzyl chloride the reaction proceeds equally well but is extremely slow it took one month to reach completion compared to 3 h with benzyl bromide. These remarkable results were extended to a variety of benzylic substrates and secondary phosphines (Table 6.12). In these reactions instead of using the rather sensitive complexes 73 or analogues, the air-stable precursor Pt((7, 7 )-Me-DuPhos)(Q)(Ph)] was employed. 

A number of different types of benzyl substrates, diethyl benzylphosphonate, benzyl methyl sulfide, benzyl phenyl sulfide, benzyl benzoate, benzyl phenyl ether, and benzyloxytrimethylsilane were also reacted with Mn. Unfortunately, according to TLC and/or gas chromatography analyses, no oxidative addition occurred with these substrates. 

A new cyclization of activated alkenes (137), involving addition of benzylic substrates (138) and catalysed by IrCl3, has been developed. The reaction proceeds with a C-H activation of the benzylic substrate in a radical manner and gives rise to indolones (139)... 

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