direct synthesis of 3-substituted isocoumarinfrom 4-hydroxycoumarin and a benzyne precursor is developed. This synthetic strategy proceeds via C–O and C–C bond cleavage as well as C–O and C–C bond formations in a single reaction vessel by simple treatment with CsF in the absence of catalyst. This methodology affords moderate to good yields of 3-substituted isocoumarins and is tolerant of a variety of