ADVANCES IN SILOXANE-BASED COUPLING REACTIONS: APPLICATION OF PALLADIUM-MEDIATED ALLYL-ARYL COUPLING TO THE SYNTHESIS OF PANCRATISTATIN DERIVATIVES. THE FORMAL TOTAL SYNTHESIS OF (±)-7-DEOXYPANCRATISTATIN

Palladium-mediated coupling of an allylic carbonate and an aryl siloxane has been applied to the formal total synthesis of 7-deoxypancratistatin and pancratistatin analogues. The key coupling reaction involved the use of a novel palladium olefin complex resulting in regio- and stereoselective arylation yielding a tetracyclic A-C ring intermediate. The observed regioselectivity of the coupling reaction was consistent with a model in which an unsymmetrical pi-allyl palladium complex was formed. Coupling of a variety of substituted phenyl siloxane derivatives was achieved using the new Pd(0) system to provide access to novel pancratistatin derivatives.