Model Studies towards Functionalized Bisbenzannulated [5,6]‐Spiro­ketals

Following up on our previous model studies on the synthesis of simple bisbenzannulated [5,6]-spiroketals we here report the preparation of 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 nucleophilic substitution of the benzylic hydroxy group of the previously described C-3-hydroxylated spiroketal. By applying these methods we could synthesize new methyl-substituted, hydroxylated, halogenated and amino-substituted bisbenzannulated [5,6]-spiroketals in good overall yields.