prov:value
| - ##STR32## in which Z is O or C(CN)2 ; and ##STR33## in which X and Y are individually O, S, SO2, CH2, CHR, CRR', or NR; and R and R' are individually hydrogen; saturated aliphatic of from 1 to 24 carbon atoms, for example, propyl, t-butyl, heptyl, and the like; aryl of from 6 to 20 carbon atoms, for example, phenyl and naphthyl; or halo such as chloro, fluoro, and the like; or R and R' individual
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