Asymmetric Organocatalytic Formal Alkynylation and Alkenylation of α,β-Unsaturated Aldehydes

A highly stereoselective organocatalytic one-pot protocol for the formal alkynylation and alkenylation of alpha,beta-unsaturated aldehydes using novel chemistry based on beta-keto heterocyclic sulfones is presented. The organocatalytic step is catalyzed by a prolinol derivative and allows for the formation of important optically active compounds. Further transformations of the beta-keto heterocyclic sulfone moiety, based on new developments of the Smiles rearrangement through a process parallel to the Julia-Kocienski reaction, were performed leading to beta-alkynylated aldehydes and 3-alkenylated alcohols. The scopes of both transformations are demonstrated by the synthesis of various optically active alkynes and alkenes. Furthermore, different transformations of the aldehyde and the alcohol functionality were performed. Finally, the proposed mechanisms for both the alkynylation and alkenylation of alpha,beta-unsaturated aldehydes are outlined.