Z is selected from the group consisting of oxygen, sulfur, and a carbon-carbon bond, ##STR4## wherein R can be aryl (having from 6 to about 20 carbon atoms, such as phenyl) or acyl (having from 2 to about 20 carbon atoms, such as acetyl, or benzoyl), and ##STR5## wherein R1 and R2 are selected from the group consisting of hydrogen, alkyl radicals having from 1 to about 4 carbon atoms, and alkenyl