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

Abstract

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.

C-1 or C-3? By applying suitable methods new functionalized [5,6]-spiroketals were regioselectively generated as model compounds for rubromycin-type natural products.

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