Stereoselective Meisenheimer rearrangement using BTAa's as chiral auxiliaries

The Meisenheimer rearrangement involves the [2,3]-sigmatropic rearrangement of allylic tertiary amine-N-oxides to O-allyl hydroxylamines. Various BTAa's (bicycles derived from tartaric acid and alpha -amino acids) were employed as chiral auxiliaries in the Meisenheimer rearrangement of the N-oxides of N-allylamines obtained by the coupling of BTAa's with cinnamyl bromide and (E) -2-methyl-2-pentenyl acetate. While the formation of the N-oxides was highly diastereoselective, the asymmetric induction in the rearrangement was generally low. However, the interaction between the 4-endo group on the BTAa and a 2'-substituent on the allylic moiety allowed a more efficient chirality transfer in the [2,3]-sigmatropic process, affording d.e. values as high as 6S% in the best case. The cleavage of the N-O bond in the rearrangement products was possible by using Mo(CO), with a good recovery of both alcohol and chiral auxiliary. (C) 2000 Elsevier Science Ltd. All rights reserved.