Tetracyclic compounds

A compound of the formula ##STR12## wherein R.sup.3 and R.sup.4 are H or alkyl;

• R.sup.5 is H, F, Cl, Br, CF.sub.3, OH, alkyl, alkoxy, NO.sub.2, NH.sub.2, alkylamino, dialkylamino, or alkanoylamino;
• R.sup.6 is H, SH, alkyl mercapto of 1-4 carbon atoms, benzyl mercapto, alkyl of 1-10 carbon atoms, phenyl, benzyl, phenoxymethyl, phenoxypropyl or the corresponding aryl group, mono- or disubstituted on the phenyl group by alkyl of 1-4 carbon atoms, OH, OR.sup.8 wherein R.sup.8 is alkyl, alkoxymethyl or acyl, each of up to 5 carbon atoms, tetrahydropyranyl, carbobenzoxy or benzyl;
• X is S, SO, or SO.sub.2 ;
• Y is O or S, alkyl, alkoxy and alkanoyl in each case each being of 1-4 carbon atoms unless otherwise indicated;
• and R.sup.11 is H or alkyl of 1-6 carbon atoms.