Oxazoline-mediated highly stereoselective synthesis of alpha,beta-substituted-beta-aminoalkanamides, potential precursors of unnatural beta2,2,3-amino acids

The reaction of alpha-lithiated-2-alkyl-2-oxazolines 1-Li with aliphatic, aromatic and heteroaromatic N-cumyl nitrones results in the stereoselective formation of N-cumyl-1,6-dioxa-2,9-diazaspiro[4,4]nonanes 3 which equilibrate with the hydroxylamino derivatives 4. Such equilibrating mixtures can be easily transformed into beta-amino alkanamides 5 under reductive conditions, whereas acidic hydrolysis with trifluoroacetic acid (TFA) furnishes high yields of beta-phenylamino alkanamides 6 via a cumene hydroperoxide- type rearrangement. Derivatives 5 and 6 provide a backbone of potentially useful unnatural beta-2,2,3-amino acids