Hetero Diels–Alder Reactions of 1-Acetylamino- and 1-Dimethylamino-1-azadienes with Benzoquinones

Treatment of bromobenzoquinone with 2 equiv. of a 1-dimethylamino-1-azadiene afforded mixtures of the corresponding 1,8-diaza-9,10-anthraquinone and 1,5-diaza-9,10-anthraquinone. Double hetero Diels–Alder reactions between 1-dimethylamino-1-azadienes and 2,6-dibromobenzoquinone afford symmetrically substituted 1,8-diaza-9,10-anthraquinone derivatives in excellent yields. 3-Substituted 1-azadienes afford aromatic derivatives, while 4-substituted or 3,4-disubstituted 1-azadienes lead to 1,8-bis-(dimethylamino)-1,4,5,8-tetrahydro-1,8-diaza-9,10-anthraquinones, which were aromatized under thermal conditions. The hetero Diels–Alder reactions could also be controlled to give isolated 7-bromo-5,8-quinolinequinones, whose treatment with a second azadiene allowed the preparation of unsymmetrical 1,8-diaza-9,10-anthraquinones.