Oxidative acetoxy lation

Palladium clusters have been reported to catalyze the oxidative acetoxy-lation of alkenes Propene reacts with acetic acid and oxygen to give allyl acetate according to... 

Strong acids enhance oxidation, and extensive transformation can be achieved at room temperature [see Eq. (9.160)]. In the absence of oxygen, side-chain acetoxy-lation and hydroxylation take place.842... 

Several synthetic procedures for the preparation of C-2-acetoxy- and methoxy-cephalosporins have been reported20). The functionalization at the C-2 position of cephalosporin 15 can be started with the oxidation of the divalent sulfur atom which produces sulfenium cation intermediates, which are precursors of C-2-substituted cephalosporins. The electrochemical conversion of cephalosporins 15 into their C-2-substituted homologs has been realized 2,). For example, the electrochemical acetoxy-lation at the C-2 position of desacetoxycephalosporin 15 is carried out in an AcOH— Ba(OAc)2—(Pt) system to give the C-2-acetoxylated products 24 (R1 = CFL,OPh R2 = Me) in 70% yield (Scheme 2-8). Electromethoxylation at the C-2 position of 15 is performed in a MeOH/CHClj—BuEtjNCl—(Pt) system to give the compounds 25 (R1 = CH2OPh R2 = CH2Ph) in 43% yield. The methoxylated product 25 can lead to the further oxidized product 26 by electrolysis in a H20/CHClj—MgC —(Pt) two-layer system. 

In the early 1970s, our attention was directed to the Wessely acetoxy-lation (13). LTA oxidation of phenolic tetrahydroisoquinolines was exploited in our laboratory to give the corresponding p-quinol acetates, which were proved to be the reactive intermediates for the aporphine synthesis (14-15)-, that is, when an electron-rich benzene ring was present in a given p-quinol acetate, C-C bond formation occurred intramolecu-larly on its acid treatment. 

Ideally, direct oxidative hydration of 1,3-butadiene is desired rather than acetoxy-lation, but the technical difficulty is very high because water is less reactive compared with acetic acid. 

Allylic C-H Bond Activation. Internal alkenes, in particular cyclic ones, can be transformed into allylic acetates in a palladium-catalyzed oxidation (eq 6). With benzoquinone as stoichiometric oxidant or electron transfer mediator, the allylic acetoxy-lation proceeds with high selectivity for the allylic product and usually in excellent yield. 

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