Palladium-Catalyzed Cross-Coupling Reactions of Highly Hindered, Electron-Rich Phenol Triflates and Organostannanes

Article abstract of DOI:10.1021/jo00028a051

The palladium-catalyzed cross-coupling reaction of highly hindered, electron-rich phenol triflates and organostannanes (Stille reaction) has been studied in a systematic manner.The following are its salient features: (1) electron-rich phenol triflates require triphenylphosphine to undergo palladium-catalyzed cross-couplings; (2) in general, efficient reactions take place only when larger-than-usual amounts (10-15percent) of palladium are employed.On the reagent side, alkyl- (methyl only), allyl-, vinyl- and alkinylstannanes undergo efficient cross-couplings with the titlesubstrates.However, some limitations to this novel entry to 2-substituted resorcinols exist in regard to both substrates and reagents.Thus, conformationally rigid (hexasubstituted) aryl triflates behave poorly, demethylation being an important side reaction.Moreover, alkyl groups other than methyl cannot be introduced because β elimination occurs more rapidly.The potentially powerful synthesis of hindered biaryls has also been studied briefly.In the present conditions, the reaction appears to be limited by the presence of ortho substituents on the arylstannane moiety.