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 C7hydroxydibenzopyrans-6-ones involving C3-acyl coumarins, selective active methylene compounds and some methyl ketones (reagent/solvent) under basic (K2CO3) conditions. Overall, our method worked by benzannulation of the existing coumarins. In this work, we used the 2-NB group (2-NB 1/4 2nitrobenzyl) as a surrogate for C7-OH to engineer the construction of the ring C of the 3hydroxydibenzopyran-6-ones. Subsequently, the photolabile 2-NB was removed under neutral conditions to reveal the C3-OH.