Synthesis of Enantiopure Functionalized Pipecolic Acids via Amino Acid DerivedN-Acyliminium Ions

The synthesis and enzymatic resolution of a novel vinylsilane-containing amino acid is described. Derivatization of this and other olefinic amino acids followed by subjection to standard N-acyliminium ion cyclization conditions provides the corresponding pipecolic acid derivatives with – in most cases – complete conservation of enantiopurity. In addition to studying the scope of this reaction, details of the N-acyliminium ion cyclization including an aza Cope equilibrium are highlighted.