Polycyclic compounds (I) can be prepared in accordance with the following reaction formula: ##STR1## wherein R.sub.1 -R.sub.8 each represents a hydrogen atom, a hydroxyl group, an alkoxyl group or a substituted or unsubstituted benzyloxy group or neighboring two groups of R.sub.1 -R.sub.8 are coupled together to form an alkylenedioxy group; and A is an alkylene group which may be substituted by one or more alkoxycarbonyl groups, an alkenylene group which may be substituted by one or more alkoxycarbonyl groups, or a group represented by any one of the following formulas: ##STR2##