Asymmetric Induction in the Claisen Rearrangement of N-Allylketene N,O-Acetals

Article abstract of DOI:10.1021/ja00288a028

Asymmetric C-C bond formation via the diastereoselective aza-Claisen rearrangement of N-allylketene N,O-acetal 1 is described.Diastereoselection noted for rearrangement 1->2 ranges from 84percent to 96percent and is a consequence of complete (Z)-N,O-acetal olefin selectivity in 1, high C_α-si-face selectivity in the rearrangement of 1 to 2, and the absence of C_α epimerization in oxazoline 2.Experiments which establish the steric bulk of the C4 appendage as a particularly important variable are also reported.Acid-catalyzed hydrolysis of rearranged oxazoline 2 completes an efficient, enantioselective synthesis of 2-substituted pent-4-enoic acid 4 and regenerates for recycling the chiral auxiliary reagent 3, initially prepared from inexpensive α-amino acids.