Synthesis of an elaborated heliquinomycin isocoumarin moiety

Synthesis of a fully functionalized isocoumarin moiety 2 of DNA helicase inhibitor heliquinomycin (1) is reported. The key step is a modified condensation reaction of diethyl bromomalonate with readily accessible phthalaldehydic acid derivative 3. Introduction of an allyl side chain is accomplished by Claisen rearrangement of allyl phenyl ether 8.