Synthesis of 1H-2-Benzopyran-5,8-dione Skeleton through a Cascade Reaction between Benzoquinone and β-Ketoester

The 1H-2-benzopyran-5,8-dione structure was synthesized by a cascade reaction through Michael addition, elimination of HBr, and O-alkylation between a dibromobenzoquinone derivative and β-ketoesters under basic conditions. The reaction using potassium carbonate and 18-crown-6 in THF was the best condition, giving 1H-2-benzopyran-5,8-dione derivatives in good yields. The UV-vis absorption spectrum and cyclic voltammogram of the synthesized 1H-2-benzopyran-5,8-dione derivative were measured, clarifying the photophysical and redox properties. 1H-2-Benzopyran-5,8-dione skeleton was found to be selectively synthesized through a cascade reaction of Michael addition, elimination of HBr, and O-alkylation between a dibromobenzoquinone derivative and β-ketoesters. The photophysical and redox properties of the synthesized 1H-2-benzopyran-5,8-dione with red color were also elucidated.