A convergent method for the rapid preparation of substituted isocoumarins is reported. The transformation takes advantage of a spontaneous intramolecular cyclization that follows the Pd-catalyzed α-arylation of aldehydes with 2-halobenzoic esters. The reaction uses an air-stable, single-component palladium catalyst and provides access to 4-alkylated isocoumarins in one step from commercial starting materials. The applicability of the method using both cyclic and linear ketones as well as transformations of the isocoumarin core is also demonstrated.