SUMMARY OF THE INVENTION
According to our invention, in its broadest aspect, we provide a compound corresponding to the general formula (I): ##STR1## in which: R is a lower (C.sub.1 -C.sub.6) alkoxy or alkenoxy;
R.sub.1 and R.sub.2, which may be the same or different, are selected from hydrogen,
SUMMARY OF THE INVENTION
According to one aspect of our invention, we provide compounds of the general formula ##STR1## wherein R represents a lower alkoxy or lower alkenyloxy group; R.sup.1 and R.sup.2, which may be the same or different, each represent a hydrogen or halogen atom, or a