Enantioselective Lactonization by π‐Acid‐Catalyzed Allylic Substitution: A Complement to π‐Allylmetal Chemistry

Asymmetric allylic alkylation (AAA) is a powerful method for the formation of highly useful, non‐racemic allylic compounds. Here we present a complementary enantioselective process that generates allylic lactones via π‐acid catalysis. More specifically, a catalytic enantioselective dehydrative lactonization of allylic alcohols using a novel PdII‐catalyst containing the imidazole‐based P,N‐ligand (S)‐StackPhos is reported. The high‐yielding reactions are operationally simple to perform with enantioselectivities up to 99 % ee. This strategy facilitates the replacement of a poor leaving group with what would ostensibly be a better leaving group in the product avoiding complications arising from racemization by equilibration. A highly enantioselective lactonization of unactivated allylic alcohols is reported under mild conditions. The transformation is catalyzed by a PdII⋅StackPhos complex and facilitates the substitution of a poor leaving group with what would ostensibly be a better leaving group in the product without selectivity issues arising from racemization.