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 |
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Authors: | Gloria Reyes‐Rangel Yamir Bandala Fred García‐Flores Eusebio Juaristi |
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Affiliation: | 1. Departamento de Química, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, México, , D.F., México;2. Instituto de Biotecnología, Universidad Nacional Autónoma de México, , Cuernavaca, Morelos, México |
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Abstract: | 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 SmI2, 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. |
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Keywords: | Asymmetric allylation chiral sulfoxides α ‐allyl‐α ‐amino acids quaternary carbons Lewis bases |
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