Stereoselective synthesis of allylic amines by rearrangement of allylic trifluoroacetimidates:: stereoselective synthesis of polyoxamic acid and derivatives of other α-amino acids

On heating in xylene under reflux, allylic trifluoroacetimidates undergo [3,3] sigmatropic rearrangement to regioisomeric allylic trifluoroacetamides. Examples include the rearrangements of the trifluoroacetimidates 16 and 73 to the trifluoroacetamides 17 and 74, which were incorporated into stereoselective syntheses of polyoxamic acid 1, and the rearrangement of the trifluoroacetimidate 26. The rearrangement was the key step in asymmetric syntheses of the (S)- and (R)-valine derivatives 37 and 48. Other examples include rearrangements of the trifluoroacetimidates 52, 54 and 56 prepared from geraniol, cinnamyl alcohol and sorbyl alcohol, respectively, and the more complex trifluoroacetimidates 62 and 69. The stereoselectivity of these rearrangements, which are somewhat faster than rearrangements of analogous allylic trichloroacetimidates, is consistent with the participation of chair-like, six-membered, transition structures.