Theoretical evidence for pyramidalized bicyclic serine enolates in highly diastereoselective alkylations |
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Authors: | Aydillo Carlos Jiménez-Osés Gonzalo Busto Jesús H Peregrina Jesús M Zurbano María M Avenoza Alberto |
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Affiliation: | Departamento de Química, Universidad de La Rioja, UA‐CSIC, 26006 Logro?o, Spain, Fax: (+34)?941‐299‐655 |
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Abstract: | A new chiral serine equivalent and its enantiomer have been synthesized from (S)- and (R)-N-Boc-serine methyl esters (Boc: tert-butyloxycarbonyl). The use of these compounds as chiral building blocks has been demonstrated in the synthesis of alpha-alkyl alpha-amino acids by diastereoselective potassium enolate alkylation reactions and subsequent acid hydrolyses. Theoretical studies were performed to elucidate the stereochemical outcome of both the formation of five-membered cyclic N,O-acetals and the subsequent alkylation process, which occurs with total retention of configuration. This feature could be explained in terms of the high degree of pyramidalization of enolate intermediates. |
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Keywords: | ab initio calculations alkylation amino acids asymmetric synthesis carbanions |
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