Switch in regioselectivity of epoxide ring-opening by changing the organometallic reagent
The regio- and stereoselective ring-opening of a 2-(2′-oxiranyl)-1,2,3,6-tetrahydropyridine using organometallic reagents is reported. The choice of the organometallic reagent determines the formation of either 2-[(R)-1-hydroxyalkyl]- or 2-[(S)-2-hydroxy-1-alkyl]-1,2,3,6-tetrahydropyridines. The formation of 2-[(S)-2-hydroxy-1-alkyl]-1,2,3,6-tetrahydropyridines is a rare example of epoxide ring-opening with retention of configuration. The process has been applied to the asymmetric synthesis of β-(+)-conhydrine and to the formal synthesis of (2S,2′R)-erythro-methylphenidate from a common precursor. Extension of the structural diversity of the process has allowed the synthesis of several β-(+)-conhydrine analogs.