Palladium acetate catalyst oxidative coupling with

Biphenyls are also by-products of acetoxylation of aromatics [92]. Their formation is favored with a palladium metal catalyst in the absence of oxidants [93-95]. Vinyl acetate undergoes oxidative coupling under similar conditions to form 1,4-diacetoxy-1,3-butadiene [99], and aromatics and heterocycles can substitute an olefinic H-atom [100] according to eq. (28) (with X = H, CN, AcO, EtO) [100-102]. 

O/t/20-arylation of benzoic acids is often preferable to ortho-arylation of benzamides if conversion of the amide moiety to other functional groups is desired. However, only a few reports have dealt with the orf/io-functionalization of free benzoic acids due to challenges that involve such transformations. The reactions can be complicated by decarboxylation of the product and the starting material. Despite those difficulties, several methods for direct o/t/io-arylation of benzoic acids have been developed. Yu has shown that arylboronates are effective in arylation of benzoic acids under palladium catalysis [59], The reactions require the presence of palladium acetate catalyst, silver carbonate oxidant, and benzoquinone. Even more interestingly, the procedure is applicable to the arylation of unactivated sp3 C-H bonds in tertiary carboxylic acids such as pivalic acid (Scheme 13) if aryl iodide coupling partner is used. Aryl trifluoroborates can also be used [60],... 

The chemistry of vinyl acetate synthesis from the gas-phase oxidative coupling of acetic acid with ethylene has been shown to be facilitated by many co-catalysts. Since the inception of the ethylene-based homogeneous liquid-phase process by Moiseev et al. (1960), the active c ytic species in both the liquid and gas-phase process has always been seen to be some form of palladium acetate [Nakamura et al, 1971 Augustine and Blitz, 1993]. Many co-catalysts which help to enhance the productivity or selectivity of the catalyst have appeared in the literature over the years. The most notable promoters being gold (Au) [Sennewald et al., 1971 Bissot, 1977], cadmium acetate (Cd(OAc)j) [Hoechst, 1967], and potassium acetate (KOAc) [Sennewald et al., 1971 Bissot, 1977]. 

Electron-rich heterocycles can also be coupled with olefins in the presence of a suitable palladium(II) catalyst. The oxidative coupling requires the use of a stoichiometric amount of palladium however, unless a suitable oxidising agent is added to the reaction. In an early example N-sulphonylated pyrrole was reacted with 1,4-naphthoquinone in the presence of an equimolar amount of palladium acetate to give the coupled product in good yield (6.92.).124... 

The Heck reactions depicted so far all involve the coupling of halopyridines and other olefins. The alternate approach, coupling of a vinylpyridine with an aryl halide is also feasible, although less commonly employed. 4-Vinylpyridine was coupled successfully with diethyl 4-bromobenzylphosphonate (7.50.) in the presence of a highly active catalyst system consisting of palladium acetate and tn-o-tolylphosphine to give the desired product in 89% yield, which was used for grafting the pyridine moiety onto metal oxides.70... 

Palladium(II) and nitrate ion with oxygen as final oxidant give an excellent yield of cyclohexenyl acetate from cyclohexene (92% at 50°C).703 The catalyst reoxidation sequence includes a palladium nitro-nitrosyl redox couple. 

Heteropolyoxametalates are often used in combination with palladium salts as catalysts in oxidation processes using dioxygen as the oxidant. Indeed, the oxidative coupling reaction of benzenes with alkenes was also successfully achieved by use of the Pd(OAc)2/molybdovanadophosphoric acid (HPMoV)/02 system [14a]. For example, reaction of benzene with ethyl acrylate using this catalytic system in acetic acid afforded ethyl cinnamate as a major product in satisfactory yield. Typically, the reaction is conducted in acetic acid at 90 °C under 1 bar of 02. After 6 h the TON is 15. This number was recently improved to 121 [14b]. 

The oxidative coupling of benzene with styrene and some paraderivatives catalyzed by palladium (II) acetate was also investigated in the presence of MIP-CD [41]. Under this condition, the approach of the reacting molecules was also required for a sufficient reaction rate, and the product itself could be a model of the transition state. Trans-stilbene was used as a template for molecular imprinting. Pd-complexes with the synthesized macroligands turned out to be effective catalysts for the oxidative coupling process (Fig. 2.13). 

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