Palladium double bonds cleaving reaction

Epoxides are normally hydrogenated in preference to saturated ketones but double bonds are usually reduced under these conditions. It is possible in some cases to selectively cleave an epoxide without saturating double bonds by the use of the deactivated catalysts recommended for the partial reduction of acetylenes (see section IV) or by the addition of silver nitrate to the palladium-catalyzed reaction mixture. " ... 

Another attractive three-component procedure involves the versatile triazene linker T1 and generates spirooctene 30 from a Mizoroki-Heck reaction of immobilized iodoarene 29 with bicyclopropylidene in the presence of an acrylate derivative (Scheme 14.9) [27, 28], The triazene moiety can be cleaved to diazonium salts which, in turn, act as substrates for Mizoroki-Heck reactions with various alkenes to give spirooctenes 31. The latter can be obtained without the double bond in the coupled alkene if palladium on charcoal is used instead of palladium acetate, hi this case, the same catalyst promotes the Mizoroki-Heck reaction and the subsequent hydrogenation [28]. 

Catellani and Lautens have independently reported unique palladium/ norbornene-catalyzed reactions of aryl halides, which mechanistically involve a reversible alkene insertion/p-carbon elimination process [11]. For example, iodobenzene reacted with 1-iodobutane and methyl acrylate to form the multiply-alkylated benzene 29 (Scheme 7.9) [12]. The following mechanism is proposed oxidative addition of phenyl iodide onto palladium generates phenylpalladium(ll) iodide. A double bond of norbornene inserts into the C-Pd bond to form an alkylpalladium species, which cleaves a C-H bond nearby to form the palladacycle 25. -Butyl iodide then reacts with 25 to form the Pd(IV) intermediate 26, which undergoes reductive elimination. Repetition of the cyclometalation/alkylation process leads to the formation of 27. Then, P-carbon elimination affords the arylpalladium species 28 together with norbornene. Subsequently, a Heck-type reaction takes place with methyl acrylate, giving rise to 29. 

A remarkable kinetic resolution was observed recently by Feringa and coworkers when 2-silyloxyfuran was reacted with the racemic unsymmetrical allylic substrate 86, catalyzed by the palladium complex of Trost s ligand (/ ,/ )-14, as illustrated in Scheme 5.28. The acetate anion liberated upon oxidative addition of palladium(O) is assumed to cleave the silyl protecting group, so that the enolate anion forms aside from TMSOAc. After allylic alkylation of that enolate, double bond migration leads to butenolide (R)-87 isolated in 47%, if the reaction was run with 52% conversion. Not only the product 87 but also the recovered acetate... 

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