GENERAL SYNTHETIC ENTRY TO HIGHLY-OXYGENATED, ANGULARLY-FUSED POLYCYCLIC AROMATIC-COMPOUNDS

A convergent and efficient synthesis of highly-oxygenated, angularly-fused polycyclic aromatic compounds has been developed. Nucleophilic addition of [4-(tri-n-butylstannyl)phenyl]lithium to a 3,4-disubstituted-cyclobutene-1,2-dione followed by appropriate protection of the hydroxyl group and thermal rearrangement of the O-protected addition product generated a 1,4-dioxygenated-2,3-disubstituted-6-(tri-n-butylstannyl) naphthalene. Stille coupling of the 6-(tri-n-butylstannyl)naphthalene with a 4-chloro-2,3-disubstituted-2-cyclobutenone and thermolysis of the coupled product gave highly-oxygenated phenanthrenes. An isomeric series of compounds was generated from [3-(tri-n-butylstannyl)phenyl]lithium. Substituted phenanthrenes at higher overall levels of oxygenation were prepared by (1) thermolysis of the adduct obtained by addition of a lithiated naphthalene, generated by Sn --> Li exchange from a 1,4-dioxygenated-2,3-disubstituted-6-(tri to a cyclobutenedione or (2) thermolysis of the double adducts generated by reaction of 2 equiv of a cyclobutenedione with either 1,4-dilithiobenzene or 1,3 dilithiobenzene. Phenanthrenes at lower levels of oxygenation were prepared by the palladium-catalyzed cross-coupling/thermolysis of 2 equivalents of a 4-chlorocyclobutenone with either 1,4-bis(tri-n-butylstannyl)benzene or 1,3-bis(tri-n-butylstannyl)benzene.