Enantioselective Protonation of Enolates and Enols

Enantioselective protonation, until recently a largely overlooked reaction, has, in the last five years, developed into a field of intense research activity. The progress achieved parallels or complements that obtained in the understanding of enolate structures and reactivities. The conceptual simplicity and attractiveness of enantioselective protonation results from the fact that after reaction, the chiral proton donor is regenerated in its original protonated form by an extractive workup. Enantioselective protonation has been applied to the synthesis of amino acids, antiinflammatory agents (2‐arylpropanoic acids), and fragrance compounds such as ( S )‐α‐damascone, for which its industrial feasibility has been demonstrated.