A New Synthesis of (2S)-4-Oxopipecolic Acid by Thermal Rearrangement of Enantiopure Spirocyclopropaneisoxazolidine

A novel synthesis of (2S)-4-oxo-pipecolic acid is reported. The synthetic route employs as a key step the diastereoselective cycloaddition of the N- glycosylnitrone 7 to methylenecyclopropane followed by thermal rearrangement of the spirocyclopropaneisoxazolidine 8a. Stereoselective reduction of the N- BOC methyl ester of 4-oxopipecolic acid by L-selectride® gives the protected cis-4-hydroxy-pipecolic acid 14