Polycyclic compounds

A compound of the formula:

• ##STR118## wherein A is chloro, bromo or iodo;
• R.sub.1 is alkyl of 1 to 6 carbon atoms, unsubstituted or substituted with hydroxy, amino, alkanoylamido of 1 to 6 carbon atoms, benzyloxycarbonylamido or p-nitrobenzyloxycarbonylamido;
• phenyl;
• or phenyl substituted by one or more members selected from the group consisting of halo, alkyl of 1 to 6 carbon atoms, alkoxy of 1 to 6 carbon atoms, amino, alkanoylamido of 1 to 6 carbon atoms, benzyloxycarbonylamido or p-nitrobenzyloxycarbonylamido;
• R is alkyl of 1 to 6 carbon atoms, benzyl, p-nitrobenzyl, p-methoxybenzyl, phenacyl, p-bromophenacyl, 2,2,2-trichloroethyl, phthalidyl, phthalimidomethyl, .alpha.-ethoxycarbonyloxyethyl or alkanoyloxymethyl of 1 to 6 carbon atoms, and
• G is hydrogen, alkyl or alkenyl, said alkyl and alkenyl being unsubstituted or substituted with hydroxy, oxy, methoxycarbonyl, phenyl or phenyl substituted with alkyl of 1 to 6 carbon atoms, alkoxy of 1 to 6 carbon atoms, nitro or halo.