Benzenepolycarboxylate

Table 3. Physical Properties of Anhydrides of the Benzenepolycarboxylic Acids...

Table 4. Melting Points of the Full Methyl Esters of Benzenepolycarboxylic Acids...

In spite of this variation in molecular weights and solubilities humic acid and fulvic acid have a very similar chemical composition. These acids consist of aromatic moieties such as phenols, benzenepolycarboxylic acids, hydroxybenzenepolycarbo-xylic acids, 1,2-dihydroxybenzene carboxylic acids, together with more complex condensed structures and polycylic compounds. It is conjectured that these various units are joined together by aliphatic chains (45, 54) the distribution of functional groups is presented in Table 5. 

The enantiodifferentiating photoisomerization of (Z )-cycloheptene 36Z was also studied in some detail [163]. Low temperature irradiations of 36Z in the presence of chiral benzenepolycarboxylates as sensitizers give the labile (ii)-isomer 36E, which is subsequently trapped in the dark by either 1,3-diphenylisobenzofuran or osmium tetraoxide to afford the adduct 88 or the diol 89, respectively (Sch. 33). The observed photostationary-state EfZ ratios of 0.1 are comparable or slightly lower than that obtained for the singlet-sensitized photoisomerization of (Z)-cyclo-octene 38Z. The ee of... 

Finally, benzenepolycarboxylates were obtained by ruthenium-catalyzed cross-benzannulation of acetylenedicarboxylates with allylic compounds [52] (Eq. 39). A ruthenacyclopentene is postulated to occur via oxidative coupling of one molecule of alkyne with allylic alcohol. Subsequent insertion of another molecule of alkyne gives the corresponding polysubstituted benzene derivatives. 

In contrast, the more electron-rich 1,2-dianisylcyclopropane 32 and 1,2-diphenyloxirane 33 gave merely racemic trans isomers 32t and 33t (ee < 1%) upon sensitization with chiral benzenepolycarboxylates 45 and 46 in pentane or acetonitrile [25]. This was attributed to the intervention of a radical cationic or zwitterionic ring-opened intermediate, which freely racemizes in the absence of a chiral sensitizer in its vicinity, particularly in polar solvents. 

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