New method for synthesis of 7-hydroxydibenzopyran-6-ones: Benzannulation of coumarins by three-component condensation.

We have achieved a simple, facile and three-component synthesis of C8 and C9 alkyl/aryl C7-hydroxydibenzopyrans-6-ones involving C3-acyl coumarins, selective active methylene compounds and some methyl ketones (reagent/solvent) under basic (K 2 CO 3) conditions. Overall, our method worked by benzannulation of the existing coumarins. In this work, we used the 2-NB group (2-NB = 2-nitrobenzyl) as a surrogate for C7–OH to engineer the construction of the ring C of the 3-hydroxydibenzopyran-6-ones. Subsequently, the photolabile 2-NB was removed under neutral conditions to reveal the C3–OH. [Display omitted] [ABSTRACT FROM AUTHOR]