prov:value
| - R1, R2, R3 and R4 are substituted or unsubstituted alkyl or aryl group which may be the same or different such as phenyl, 4-methylphenyl, 2,4,6-trimethylphenyl, 2,4,6-trimethoxyphenyl, 2,3,4,5,6-pentafluorophenyl, methyl, ethyl, propyl, butyl, isopropyl, cyclohexyl, t-butyl, octyl and the like.
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