Isomerisations of cycloalkene- and bicycloalkene-derived achiral epoxides by enantioselective α-deprotonation

Abstract

Enantioselective α-deprotonation–rearrangement of cis-cyclooctene oxide 1 using organolithiums in the presence of (–)-sparteine 4 or (–)-α-isosparteine 5 gives the (–)-alcohol 2 in good yields and ees. The use of C₂-symmetric bisoxazolines (–)-6a–d as ligands allows access to the (+)-alcohol 2. (–)-α-Isosparteine 5 functions as an efficient asymmetric ligand catalyst in the rearrangement of 1. The α-deprotonation process can be extended to other cycloalkene-derived achiral epoxides 7, 9, 11, 15 and 19. Lithium amide-induced transformations of rigid bicycloalkene-derived epoxides (25, 34 and 42) are described, providing insight into the rearrangement mechanisms which operate following α-lithiation in such systems. The enantioselective α-deprotonation–rearrangement of bicycloalkene-derived epoxides (25, 29 and 42) to ketones (28, 33 and 44 respectively) is described.