STILLE COUPLING VERSUS CINE SUBSTITUTION - ELECTRONIC EFFECTS ALSO INFLUENCE COUPLING STERICALLY HINDERED STANNANES

Very low ligand to palladium ratios, especially weak ligands and iodid es as electrophiles allow Stille couplings to very hindered stannanes, not possible under common conditions. In contrast, the usage of trifl ates and elevated temperatures yields exclusively the product of a Cin e substitution. In this way, by the choice of the reaction conditions, two alternative stereoisomers can be obtained from the same stannane. (C) 1998 Elsevier Science Ltd. All rights reserved.