[GRAPHICS]A highly flexible synthesis of bisbenzannulated spiroketals is described with additions of lithiated methoxyallene to aryl aldehydes and Heck reactions as key steps. Subsequent hydrogenations and ketalizations afforded the desired spiroketals in good yields and with predominating trans-configuration. With model compound 30, already bearing the fully substituted naphthyl core of rubromycins, the ketalization proceeded efficiently providing the expected product 31 and the isopropoxy compound 32. Both products are advanced model compounds of heliquinomycin.
Model Studies towards Functionalized Bisbenzannulated [5,6]-Spiroketals
new examples of this entity with a variation in their substitution pattern. The regioselective introduction of functional groups in the C-3 or C-3′ positions (rubromycin numbering) may either take place prior to the spiroketalization by α-functionalizations of the ketone moiety of the precursor or in a subsequent step by the nucleophilicsubstitution of the benzylic hydroxy group of the previously described