Bispalladacycle Catalyzed Nucleophilic Enantioselective Allylation of Aldehydes by Allylstannanes

Abstract

AbstractEnantiopure homoallylic secondary alcohols are very important synthetic building due to the versatility of the hydroxyl and olefin moieties. A key strategy to prepare them is by nucleophilic allylation of aldehydes. A large number of catalyst concepts emerged that allow for high enantioselectivity. Still, in many target‐oriented syntheses of complex structures stoichiometric methods are preferred over catalytic ones. The need for high catalyst loadings and long reaction times, plus unsatisfying reproducibility and substrate scopes are reasons for that. In the present study we report the first palladium catalysts capable of controlling asymmetric nucleophilic allylations of aldehydes with allyltributyltin. TONs up to 620 were achieved, which is significantly higher than for any other reported catalyst. The method is also tolerating electronically and sterically unfavorable substrates. We show that a transmetallation occurs, favoring an η1‐allyl coordination mode with the bispalladacycles. In contrast, for the corresponding monopalladacycle an unproductive η3 coordination is dominant.