Detalle de: Theoretical Evidence for Pyramidalized Bicyclic Serine Enolates in Highly Diastereoselective Alkylations

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 α‐alkyl α‐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.