Role of the Countercation in Diastereoselective Alkylations of Pyramidalized Bicyclic Serine Enolates. An Easy Approach to α-Benzylserine^†

The use of a chiral serine equivalent as an excellent chiral building block has been demonstrated in the synthesis of α-benzylserine through a diastereoselective lithium enolate alkylation reaction and subsequent acid hydrolysis. The role of a coordinating countercation (lithium) in the alkylation reaction has been investigated. Theoretical studies have been performed in order to elucidate the stereochemical outcome of the alkylation process, which occurs with total retention of configuration.