Benzoic esters, reductive cleavage

Aromatic compounds can also be degraded anaerobically, via reductive pathways, which have been reviewed. The best-characterized example is the degradation of benzoic acid in Rhodopseudomonas palustris and Thauera aromatica via the pathway shown in Figure 8. Benzoyl-CoA is formed, and then a reductase enzyme is able to reduce the aromatic ring to a cyclohexadiene. Following two consecutive additions of water, and oxidation to a /3-keto ester, hydrolytic cleavage gives a linear 7-carbon CoA thioester, which can then be broken down via fatty acid /3-oxidation. 

Ci.HjsO] H3C OT3 H3C CH3 Reductive cleavage of benzoic ester of corresp. benzyl alcohol with K Na alloy/ Benzene ESR/ 300 i3C(7) 4.45 4i3c(7,iS-CH3) 1.3 82Schl... 

Benzyloxymethyl esters can be cleaved either by catalytic reduction or by hydrolysis under mild acidic conditions. - E Benzyloxymethyl benzoate hydrogenated with 5%-Pd-on-carbon in abs. ethanol benzoic acid. Y ca. 100%. F. e. and cleavage in aq. HCl-tetrahydrofuran s. P. A. Zoretic, P. Soja, and W. E. Conrad, J. Org. Chem. 40, 2962 (1975). 

Recently, it has been shown that the BY-mediated reduction of a-substituted p-keto esters led to the reduction of the carbonyl group with high stereospecificity at low pH values, whereas at higher pH values cleavage of the C—C bond is observed. Thus, 250 gave at pH = 4 251 and 252 each of 99% e.e. with a syn anti ratio of 10 1, whereas at pH = 7 a 1 1 ratio was observed and the e.e. values were significantly lower. Finally, at pH = 8 a cleavage of the C—C bond with more than 75% formation of benzoic acid (229) was observed [361]. 

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