The use of a chiral serine equivalent as an excellent chiralbuilding block has been demonstrated in the synthesis of
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-benzylserine through a diastereoselective lithium enolatealkylation reaction and subsequent acid hydrolysis. The roleof a coordinating countercation (lithium) in the alkylationreaction has been investigated. Theoretical studies have beenperformed in order to elucidate the stereochemical outcomeof the alkylation process, which occurs with total retentionof configuration.