Asymmetric Allylation of α‐Ketoester‐Derived N ‐Benzoylhydrazones Promoted by Chiral Sulfoxides/ N ‐Oxides Lewis Bases: Highly Enantioselective Synthesis of Quaternary α‐Substituted α‐Allyl‐α‐Amino Acids

Chiral sulfoxides/ N ‐oxides ( R )‐ 1 and ( R , R )‐ 2 are effective chiral promoters in the enantioselective allylation of α‐keto ester N ‐benzoylhydrazone derivatives 3a , 3b , 3c , 3d , 3e , 3f , 3g to generate the corresponding N ‐benzoylhydrazine derivatives 4a , 4b , 4c , 4d , 4e , 4f , 4g , with enantiomeric excesses as high as 98%. Representative hydrazine derivatives 4a , 4b were subsequently treated with SmI 2 , and the resulting amino esters 5a , 5b with LiOH to obtain quaternary α‐substituted α‐allyl α‐amino acids 6a , 6b , whose absolute configuration was assigned as ( S ), with fundament on chemical correlation and electronic circular dichroism (ECD) data. Chirality 25:529–540, 2013 . © 2013 Wiley Periodicals, Inc.