Asymmetric Organocatalytic Reactions of Activated Racemic Allenes

Abstract

Asymmetric organocatalytic reactions of various electron-deficient racemic allenes with a wide variety of nucleophiles and electrophiles were reviewed. The literature on enantioselective functionalization of allenes that employs chiral phosphine, amine, phase transfer, bifunctional, and Brønsted acid catalysis is presented along with the mecha-nisms. In addition, the review emphasizes methods of obtaining enantioenriched allenes from racemic allenes via organocatalytic (dynamic) kinetic resolution techniques. The synthetic utility of the developed methodologies toward the target-orientated biologically active molecules is narrated along with the examples.

Decomposition of Alkynyl Hydrazones: Synthesis of Allenoates, Dihaloallenoates, and Angularly Fused Tricyclic Azepines

“…1 Importantly, electrondeficient allenoates are excellent synthons for various types of dipolar cycloadditions, annulations, concerted reactions, cyclization reactions, nucleophilic/electrophilic additions, and rearrangement reactions. 2 These reactions render various heterocycles, butenolides, allylic esters, and useful scaffolds. Significant advances have been witnessed in recent decades in the construction of synthetically useful electron-deficient cumulated diene systems.…”

“…It is evident that the allenoates do possess multiple reactive pathways in the presence of nucleophilic catalysis, thereby opening diverse possibilities that could provide multiple products. 2 However, to our delight, we observed exclusively one product with excellent diastereoselectivity (>20:1 dr). Finally, we validated the optimized conditions with a different amidine (DBN), and the reaction afforded product 7l in 66% yield.…”