Base Catalyzed Asymmetric Induction of the Reaction of Methyl(phenyl)ketene with 1‐Phenylethanol: Method of Obtaining Hydratropic Acid in High Enantiomeric Purity

The conversion of (±)-hydratropaoyl chloride into (S)-(+)-hydratropic acid (4) can be achieved with (S)-(−)-1-phenylethanol (2) as chiral auxiliary agent in the following way: Generation of the ketene (1) from the acid chloride in situ, reaction with (S)-(−)-(2) in the presence of a base to give a mixture of the diastereomers (3) [with pyridine, e.g., (S,S) :(R,S) = 88 :12], hydrolysis of (S)-(+)-(4) with recovery of (S)-(−)-(2).