Polycyclic hydroxyquinones. XXVII. Tautomerism in 1,4-Dihydroxy-9,10-anthraquinone Monoimines. Cycloaddition Reactions of Their 1,4-Anthraquinonoid Tautomers
substituted derivatives thereof (6a-i) have been prepared by ammonolysis of the corresponding 1,4-dihydroxy-9,10-anthraquinones. 1H- and 13C-n.m.r. studies show the existence of a rapid tautomeric equilibrium in quinone imines of type 6. Diels-Alderreaction with the 1,4-anthraquinonoid tautomer of quinone monoimines 6a,e affords ABCD tetracyclicsystems related to those existing in anthracyclinones.