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Organocatalytic Doubly Annulative Approach to 3,4-Dihydrocoumarins Bearing a Fused Pyrrolidine Scaffold.

A new strategy for the highly enantio- and diastereoselective synthesis of 3,4-dihydrocoumarin derivatives bearing a fused pyrrolidine ring is reported. It is based on a Brønsted base catalyzed cascade reactivity between β,γ-unsaturated-α-ketophosphonates and imines (derived from various salicylaldehydes and diethyl aminomalonate). The approach can be described as a doubly annulative strategy where both the pyrrolidine moiety and the δ-lactone ring of the 3,4-dihydrocoumarin framework are constructed starting from acyclic precursors.