Enantioselective Synthesis of α-Fluoro-β3-amino Esters: Synthesis of Enantiopure, Orthogonally Protected α-Fluoro-β3-lysine

The scope of a tandem conjugate addition−fluorination sequence performed on α,β-unsaturated esters using the enantiopure lithium amide derived from (S)-N-benzyl-N-(α-methylbenzyl)amine, and the electrophilic fluorinating agent N-fluorobenzenesulfonimide has been investigated. Using this method, α-fluoro-β3-amino esters can be obtained in up to quantitative yield and 80:20 to >99:1 dr. This simple methodology does not rely on the use of α-amino acids from the chiral pool and thus provides the potential for the preparation of enantiopure α-fluoro-β3-amino acids with a wide variety of side chains. Its utility was demonstrated through the synthesis of orthogonally protected (2S,3S)-α-fluoro-β3-lysine.