Ketones from Wacker type oxidation

Wacker-type oxidation. " Methyl ketone formation from RCH=CH2 is effected with H2O2 in the presence of (Ph3P)4Pd. 

To explain the observed behavior, it has been suggested [163,164,169,171] that the oxidation of terminal olefins to methyl ketones takes place via two complementary reactions occurring in a coupled mode (Scheme 12). These reactions are the activation of dioxygen (path A) and a Wacker type oxidation (path B). In path A, the cationic rhodium(II) complex 17, formed from RhCl, olefin, EtOH and... 

The findings of Sen and Halpern (36, see Reaction 7) suggest alternative pathways for the Rh-catalyzed co-oxidation, in which the phosphine is oxidized by liberated peroxide and the ketone is formed during the reduction of Rh(III) to Rh(I) (a Wacker cycle). Read and Walker (87) ruled out Wacker chemistry, since addition of water in their system (OH is needed for the reduction, Reactions 7 and 8) decreased ketone yield somewhat. More convincing evidence for the absence of Wacker type chemistry comes from isotope studies using H2018, work just published by Tang et al. (89). 

Pd/Cu-coupled catalysis has been used in many Wacker-type olefin oxidations other than those that involve Markovnikov methyl ketone formation from terminal olefins [la,b, 21]. Pd/Cu-coupled aerobic oxidation systems have also been widely appfied to other sp and sp carbon oxidations. Selected examples of these oxidations, including those involving carbon nucleophiles, oxidative carbo-nylations and oxidative coupling reaction, are pictured in Scheme 5.7 [22, 26]. 

Also, other ten-membered lactones can be conveniently prepared starting from the primary acetates, as outlined in Equation 6. Again the terminal double bond of the telomer is oxidized in a Wacker—Hoechst-type reaction yielding a methyl ketone. After conversion into an allylic chloride and treatment with phenylthioacetylchloride an intramolecular alkylation yields the lactone-ring [8]. 

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