Palladium -catalyzed hydroxyl-directed

We do not know if the vinylic alcohol is actually an intermediate or whether a hydride-71 complex of it rearranges directly to the aldehyde as probably happens in the palladium-catalyzed oxidation of ethylene to acetaldehyde. The formation of 4% 2-methyl-2-phenylpropanal is unexpected. This product must arise from a reversed addition of the phenylpalladium group followed by a hydrogen transfer from the hydroxyl-bearing carbon to the palladium, followed by reductive elimination of a hydridopalladium group. An alkyoxypalladium intermediate has been proposed (39). 

The boryl groups installed on the aromatic polymers are useful synthetic intermediates for conversion to other polar functional groups. For example, they can be oxidized to give hydroxylated polymers and a variety of polar group-containing polymers via either direct functional group transformations or palladium-catalyzed Suzuki cross-coupHng reactions with appropriate phenyl bromides (Fig. 25). This transition metal-catalyzed polymer... 

Considering the similarity of the hydroxyl group in alcohols and silanols, Gevorgyan developed a silanol-directed palladium-catalyzed C-H activation/C-O cyclization of phenoxy silanols [61]. The obtained oxasilacycles were further desilylated with TBAF to give catechols. In a follow-up work, the same group disclosed a palladium-catalyzed C-H oxygenation with benzylsilanols to achieve oxasilacycles under similar conditions (Scheme 3.32) [62]. The obtained oxasilacycles proved to be valuable synthetic intermediates and could be converted to a variety of useful compounds. 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

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