A short and efficient formal synthesis of (R)-pipecolic acid from the ring expansion of chiral aziridine

Ring expansion of 4-[(2R)-1-[(1R)-1-phenylethyl]aziridin-2-yl]butyl tosylate obtained from tosylation of 4-[(2R)-1-[(1R)-1-phenylethyl]aziridin-2-yl]butan-1-ol via formation of 1-azabicyclo[4.1.0]heptane tosylate gives substituted piperidine. The ring openings of azabicycloheptane tosylate with acetate nucleophiles proceeded in highly regio- and stereoselective manner with release of the ring-strain of the three-membered aziridine ring through the breakage of either C-N bond. This ring expansion streategy of aziridine provides a short route for asymmetric synthesis of biologically active natural alkaloid such as (R)-pipecolic acid.