Carboxylic acid anhydrides decarbonylation

Because stoichiometric amounts of base-HX salts are produced in a Heck reaction, alternative sources of aryl groups have been investigated. Carboxylic acid anhydrides were found to react with a PdC2/NaBr catalyst system, where the by-products were CO and a carboxylic acid, p-Nitrophenylbenzoates were also found to be aryl donors in a decarbonylative Heck reaction. An arylation of cinnamates was discovered using Pd(OAc)2 to activate... 

Iodine mercuric oxide ozone Carboxylic acid esters from carboxylic acid anhydrides by oxidative decarbonylation... 

Aliphatic carboxylic acids undergo decarbonylation-dehydration to afford 1-alkenes of one less carbon atom in high yields with surprisingly high selectivity by the treatment of an equimolar mixture of a carboxyhc acid and acetic anhydride at 250 °C (bath temperature). It was confirmed that the mixed anhydride is the intermediate of the reaction. The decarbonylation-dehydration occurred by heating an equimolar mixture of decanoic acid and acetic anhydride in the presence of PdCl2(Ph3P)2 (0.01 mol %) and excess PhsP (50 equiv relative to the Pd catalyst) to afford 1-nonene with a selectivity of 97.3% and a catalyst turnover number (TON) of 12370. It seems likely that Pd(0) coordinated by PhsP does not catalyze isomerization of double bonds (Scheme 5). 

Removal of the furan ring (148) was accomplished in two steps in 45% overall yield from carboxylic acid 125 (Scheme 24) [57]. Carboxylic acid 125 was coupled with selenophenol via the mixed anhydride using phenyl dichlorophosphate to give the phenyl seleno ester. Decarbonylation of the phenyl seleno ester was accomplished with tributyltin hydride and AIBN in toluene. 

In 2012 Ryu and his colleagues reported the iron-catalyzed decarbonylation of aliphatic carboxylic acids to a-olefins (Scheme 11.7) [32]. In their mechanism study, they found the formation of CO but not CO2. If the reaction was carried out under low or no pressure (0-5 bar) of carbon monoxide, internal an olefin was observed [33]. In the proposed reaction mechanism, the reaction starts from acid anhydride, which was produced from the reaction of substrate and AC2O. Then it reacts with the in situ-formed iron-carbonyl complex, which was generated by FeCl2, phosphine ligand, KI, and CO, and decarbonylation occurred under high temperatures. Notably, Fe2(CO)9, Fe3(CO)i2, [Fe(CO)2Cp]2 did not give the decarbonylation product. 

On the other hand, the oxidative addition of aliphatic acid chlorides occurs in the absence of alkyne, but the oxidative addition complex could not be isolated due to fast decarbonylation followed by facile /1-hydrogen elimination. The decarbonylation of carboxylic acid was reported with palladium catalysts as well [47-56], In general, the reactions to acid anhydride as the intermediate need relatively high temperatures. 

A similar Pd-mediated decarbonylation reaction involves the conversion of aromatic carboxylic acids in situ to mixed anhydrides by treatment with di-f rf-butyl dicarbonate, which are then vinyl-ated with extrusion of CO. AH by-products were found to be volatile, which makes product isolation particularly easy (Scheme 22.27) [39]. 

In 2013, Ryu and coworkers reported a rhodium-catalyzed arylation of 2-aryloxybenzoic acids through decarbonylative intramolecular C-H functionalization (Scheme 6.14) [24]. The existence of AC2O andKl could significantly enhance the reactivity. Based on the control experiments, a mixed anhydride will be produced through the condensation reaction of carboxylic acid and AC2O, which oxidize the rhodium(I) catalyst to rhodium(III) species. 

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