Benzoic anhydride, III

Acetylation, formylatlon, and benzoylation of a variety of primary and secondary alcohols with the respective acids (acetic acid or anhydride, ethyl formate, and benzoic anhydride) can be achieved under the catalysis of BiCls, Bi(OCOCF3)3, or Bi(OTf)3 (Scheme 14.97) [194—196]. The O-acylahon of phenols is also promoted by these Lewis acids. Among the bismuth(III) salts employed, Bi(OTf)3 is the most effechve in terms of reaction condihons and yields of the esters. The Bi(OTf)3-acid anhydride procedure is apphcable to the acylahon of sterically demanding or tertiary alcohols and phenols. Treatment of terhary or benzylic bromides with Bi(OCOR)3 (R=Me, Ph) affords the corresponding esters [197]. In the presence of a catalytic amount of 612(804)3, the esterificahon of cis-(-)-thujopsene with a series of C2-C8 acids proceeds in moderate yield [198]. 

Diarylketones are also the important fine chemical intermediates, which could be prepared by the acylation of aromatic hydrocarbon with benzoyl chloride and benzoic anhydride. The ionic liquids have also been used to catalyze the synthesis of diarylke-tone. Earle et al. [105] have reported the benzoylation of benzene, derivants of benzene (toluene, anisole, isobutyl benzene, phenyl chloride and fluoride) to synthesize the diarylketone by use of chloroindate (III) ionic liquids as the green dual catalysts and solvents. As a result, good yields (75-96%) were obtained under proper conditions with the ionic liquids as the clean reaction medium and recyclable catalysts. 

Hard Lewis acid chloroaluminate ionic liquids show intense catalytic activity in the Friedel-Crafts acylation reaction however, they suffer from the same issues as anhydrous aluminum chloride. i Of particular interest to these reactions, aluminum chloride may be replaced by indium trichloride to form chloroindate(III) ionic liquids. The advantage of using indium trichloride compared with aluminum chloride is represented by its hydrolytic stability and reduced oxophilicity. Chloroindate(III) ionic liquids are synthesized by mixing l-butyl-3-methylimidazolium chloride [C4mim]Cl with anhydrous indium trichloride at 80°C. In the benzoyla-tion of anisole with benzoic anhydride (BAN) at 80°C, the best yield of... 

With reference to previously reported studies of porphyrins and Schiff base complexes, the modification of the cyclic voltammogram can be explained by the occurrence of the expected formation of the high-valent manganese-oxo [Mn(V)=0]+ intermediate, followed by its reduction and the steady-state elec-trocatalytic regeneration of Mn(III) form according to the following set of reactions (where (PhC0)20 is benzoic anhydride) ... 

Figure 8.28. (a) Cyclic voltammograms (scan rate = 100 mV s ) and (b) hydrodynamic voltammograms (scan rate = 10 mV s electrode rotation rate = 400 rpm) of a vitreous carbon disk electrode modified with a film of poly[Mn(III)-32] in DCM + 0.1 mol BU4NBF4 under argon (curve 1), in the presence of dissolved oxygen (curve 2) and in the presence of dissolved oxygen and 0.1 M benzoic anhydride (curve 3). Adapted from ref. [241]... 

Mn(ni)-like Q band blue shifted by 4nm compared to the native Mn(III) one. When the reductive electrolysis is stopped (curve 3), there is a complete vanishing of the band at 688 nm to the detriment of the Mn(III)-like one at 729 nm. The Q band for the native Mn(III) film is reported for comparison (dashed curve). These observations may be explained by the formation of the doubly reduced superoxo intermediate (steps 1-3) that exhibits a Q band at 688 nm, while the formulated Mn(III)-superoxide adduct exhibits a Q band at 729 nm. When molecular oxygen was added to the reduced poly[Mn(II)-32] film in a DCM solution containing benzoic anhydride, with or without stopping the reductive electrolysis, it appears that there is a total restitution of the native film within 10 min, as it can be seen in... 

Figures 8.29c,d, respectively. No more changes in the spectra were observed when maintaining the electrolysis for more than 40 min, as far as molecular oxygen and benzoic anhydride were present in the solution. Indeed, by following the evolution of the measured current during the performed chronoamperometry, a decrease of the current during the reduction of Mn(III) to Mn(II) sites in the film was first reported. Then, the introduction of benzoic anhydride and molecular oxygen (air saturation) in the solution produced an increase in the measured cathodic current that reached a steady state indicating the establishment of the catalytic process. This can be explained by the occurrence of reactions 2-5, with steps 4 and 5 which are extremely fast compared to the UV-visible timescale.

Besides halides and triflates, other electrophiles can be applied to Heck reactions. The first classical alternative was diazonium salts. Reactions proceed in the absence of phosphine (partly due to the fact that phosphines result in uncontrolled decomposition of the diazonium salt). The Heck reaction using these species can be useful in cases when mild conditions are required. Alternatively, iodonium salts behave in a similar manner to diazonium salts and show better tolerance to bases. " The reactions take place at ambient temperature and so are once again most useful in situations when mild conditions are required. Some main group metallie eompounds such as lead(IV) and thallium(III) have also been shown to undergo Heck-type chemistry and can be useful in specific cases. Of particular interest is the fact that acid chlorides and anhydrides can be employed in Heck chemistry, the use which was pioneered by Blaser and Spencer in 1982. " The process involves oxidative addition of palladium into the C-X bond followed by decarbonylation to yield the intermediate ArPdX species, de Vries has exploited this reaction, demonstrating the use of benzoic anhydride (105) as an effective arylating agent. ... 

Bismuth(III) triflate is also a powerful acylation catalyst that catalyzes reactions with acetic anhydride and other less reactive anhydrides such as benzoic and pivalic anhydrides.113 Good results are achieved with tertiary and hindered secondary alcohols, as well as with alcohols containing acid- and base-sensitive functional groups. 

Moreover, they are versatile building blocks for the synthesis of functionalized naphthalenes, anthracenes, and naphthacene natural products [8]. Recently, Rh-catalyzed C-H activation followed by nucleophilic addition to aldehydes emerged as a powerful alternative to access phthalides. In 2012, Li and coworkers developed a novel Rh(III)-catalyzed synthesis of three substituted phthalides from benzoic acids and aldehydes through carboxylate-directed ortho-C-H functionalization and subsequent intramolecular cyclization (Scheme 6.2a) [9]. In 2013, GooCen and coworkers described the straightforward synthesis of S-alkylidenephthalides from benzoic acids and aliphatic acids or anhydrides in the presence of [Rh(cod)Cl]2 and CsF (Scheme 6.2b) [10]. 

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