Benzylic activation

Moreover, in this particular example, the distribution of mono- and bis-silylated products changes over time improved yields of the mono-silylated (sp2-functionalized product) are observed after 1 h reaction, whereas overnight reaction leads to a good yield of bis-C-H aryl- and C-H benzyl-activated product (Equation (55)).ss... 

The meta-selectivity for toluene activation, observed for both systems, is very unusual (Fig. 5). Also remarkable is the switch in selectivity from aryl C-H activation to benzylic activation inp-xylene, just by changing the chelate ligand from the diimine equipped with trifluoromethyl substitutents in the meta-positions of the phenyl residue to the diimine bearing methyl substituents in the ortho-positions (Fig. 5). The authors suggested that the C-H bond activation is reversible and the isomeric a-methane complexes are in equilibrium prior to the substitution of... 

Scheme 3. Benzylation activation of arenes by the 12-electron CpFe+ and the 13-electron CpFe groups (see also Scheme 4).

R = alkyl, aryl R = 1° or 2 alkyl, allyl, benzyl, activated aryl, acyl X - Cl, Br, I, OTs electrophile epoxide, dialkyl sulfate, alkyl sulfonate, alkyl nitrate base = NaOR NaH base = KOf-Bu, cone. NaOEt, NaH solvent = R OH, f-BuOH, benzene, ether, DMF... 

Few reports have appeared addressing the stereochemistry of either C-H bond oxidative addition or reductive elimination. The most convincing paper was an intramolecular activation examined by Flood in which a chiral 8-ethylquinoline derivative underwent benzylic activation by PdCl42-. The reaction proceeds with the net retention of configuration at carbon (Eq. 10) [49]. 

Wolczanski also investigated the chemistry of a tantalum imido system. In this system, elimination of hydrocarbon from the bis-amido imido complex occurs with difficulty at 183°C to give an amido bis-imido complex. The elimination is reversible, with the bis-imido species not being directly observed (Scheme 10). Under methane pressure, the phenyl complex loses benzene and adds methane. Neopentane, benzene, and toluene (benzylic activation) were also found to undergo activation, but not cyclohexane. The authors conclude from their equilibrium studies that the differences in metal-carbon bond strengths are approximately equal to the differences in carbon-hydrogen bond... 

Acetattzation. Diethyl acetals are formed from carbonyl compounds by functional group exchange with triethyl orthoformate (EtOH also present) under the influence of DDD." Benzylic activation. Hydride abstraction by DDQ from benzyl ethers, where the benzylic position is also activated by a nuclear substitutent (e.g., methoxy group), prepares such compounds to be attacked by nucleophiles. The reaction constitutes an important step in a synthesis of deoxyfrenolicin. ... 

Benzylation Active methylene coi r ecnophile in the presence of KjCOj in refl... 

Benzylation Active methylene compounds undergo monobenzylation with this electrophile in the presence of K COj in refluxing DMF. Phenols are 0-benzylated. 

Cp cyclopentadienyl. Me methyl,/nd indenyl,/ndW. tetrahydroindenyl,iin C2H4,F/m fluoremyl, NmCp neomenthyl cyclopentadienyl, Bz benzyl Activity is expressed as kgpE/(moln,etaUocene h [ethene])... 

---