Acetate, catalysis

This results in a pH-rate profile as shown in Fig. 8.P21, with the acetate catalysis being signifieant in the pH range 3-6. Discuss how this catalysis by acetate ion might oeeur. What are the most likely mechanisms for hydrolysis at pH < 2 and pH > 7, where the rates are linear in [H+] and [ OH], respectively ... 

Intramolecular cyclization. Knoevenagel condensation of diphenylacetaldehyde with diethyl malonate (piperidinium acetate catalysis) results in only a trace of the expected product when molecular sieves are present, the a-naphthol 1 is formed in 52% yield.2 A similar reaction is observed with ethyl acetoacetate and ethyl benzoylacetate. 

Oxathiocin formation occurs only in very special circumstances when the thiophene ring is substituted with chlorine at the 2- and 5-positions of the ring (88CC138). Reaction of ethyl diazoacetoacetate with 2,5-dichloro-thiophene under rhodium(II) acetate catalysis results in the formation of 2-methyl-3-ethoxycarbonyl-5,8-dichloro-l,4-oxathiocin (26, R = H, R = COjEt, R = CHj) (Scheme 3). In this reaction the intermediate ylid is not observed and the only isolated product is the oxathiocin. However, when diazodimedone (27) is used, the intermediate ylid has been isolated and... 

General base catalysis by formate, acetate, imidazole, phosphate, and methoxyamine is also observed in the hydrolysis of ethyl trifluorothiol-acetate the Bronsted exponent j8 is 0 33. In acetate buffers a careful kinetic study demonstrated inhibition by acetic acid. Therefore, the acetate reaction also involves a tetrahedral intermediate according to scheme C. No complex formation of the substrate with acetic acid, which could alternatively cause inhibition, could be found. Scheme C accounts for the acetate catalysis and inhibition by acetic acid. In scheme C, a general base mechanism is written, the same mechanism which unequivocally applies to the water reaction. 

Concurrently, Noels had reported that rhodium carboxylates smoothly catalyze the intermolecular C—H insertion of ethyl diazoacetate into alkanes. Following up on this report, Taber demonstrated that the open chain a-diazo 3-keto ester (60) cyclizes smoothly under rhodium acetate catalysis to give the corresponding cyclopentane (61 equation 24). In contrast to the copper-mediated cyclization cited above (equation 22), the six-membered ring product is not observed. The insertion shows significant electronic selectivity. Although there is a 3 1 statistical preference for methyl C—H, only the methylene C—H insertion product (61) is observed (equation 24). 

Other elecuon-withdrawing groups are compatible with both diazo transfer and cyclization. Both the -keto sulfone (65) and the -keto phosphonate (67) have been cyclized using rhodium acetate catalysis (equations 25 and 26). The cyclized keto phosphonate (68) can be further reacted with formaldehyde to make the a-alkylidenecyclopentanone (69 equation 26). ... 

Figure 3 Browning (A420) of glucose (0.2 M) - acetate (0.5 M) or citrate (0.5 M) with and without glycine (0,0.2 M), pHj 5.5 50 C. mechanism of acetate catalysis is not understood and requires further investigation.

The a,/J-unsaturated acetal 24 reacts with diazomethane under palladium(II) acetate catalysis to provide the oxazolidinyl-substituted cyclopropane 25 with high diastereomeric purity. Subsequent hydrolysis gives (-)-(l,R,2/ )-fraft.v-2-phenylcyclopropanecarboxaldehyde with recovery of the ( —)-2-methylamino-l-phenyl-l-propanol [(-)-ephedrine] auxiliary79. 

In contrast, the S,C-ylide (139a) prepared from tetrachlorothiophene and diazomalonic ester under rhodium acetate catalysis undergoes cycloaddition with acenaphthylene much more slowly however, after heating at 80 °C for 7 h, the reaction leads to the aromatized fluoranthene (226) in 97% yield. The formation of (226) involves a proton shift and loss of chlorine the exact mechanism and the location of the chlorine atoms are not clear <86JCS(Pl)233>. 

Recrystallization from boiling MeOH (15 mL/g) yielded, after filtration and air drying, beta-nitro-3,4,5-trimethoxystyrene as bright yellow crystals weighing 18.5 g. An alternate synthesis was effective, using an excess of nitromethane as solvent as well as reagent, if the amount of ammonium acetate catalysis was kept small. 

Ren B, Rahm M, Zhang X, Zhou Y, Dong H (2014) Regioselective acetylation of diols and polyols by acetate catalysis mechanism and application. J Org Chem 79 8134... 

The effect of ortho- and weto-substitution in the above-mentioned intramolecular Buchner reactions has been examined. When the 2-methoxy-substituted diazoketone 32 is subjected to rhodium(II) acetate catalysis, a single cycloheptatrienone 34 is obtained in 94% yield.This result is consistent with the outcome of the rhodium(II) trifluoroacetate-catalyzed intermolecular reaction of ethyl diazoacetate with anisole, which yields no product arising from addition of the ketocarbenoid on the most hindered site of the anisole. Dihydroazulenone 34 rearranges to tetralone 36 under acidic conditions, and isomerizes to the conjugated ketone 35 under basic conditions. It is interesting that the catalyzed decomposition of the para-methoxy derivative 37 provides exclusively 6-methoxy-2-tetralone 40 with no trace of the putative trienone 39. ... 

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