Allylic trifluoroacetimidates

Jautze S, Seiler P, Peters R (2008) Synthesis of nearly enantiopure allylic amines by Aza-Claisen rearrangement of Z-configured allylic trifluoroacetimidates catalyzed by highly active ferrocenylbispalladacycles. Chem Eur J 14 1430-1444... 

Savage, I., Thomas, E. J. Asymmetric a-amino acid synthesis synthesis of (+)-polyoxamic acid using a [3,3]allylic trifluoroacetimidate rearrangement. J. Chem. Soc., Chem. Common. 1989, 717-719. 

Spectroscopic studies have demonstrated that a palladium catalyst for the asymmetric rearrangement of allylic trifluoroacetimidates possesses in the activated oxidized form a Pd(III) centre bound to a ferrocene core that remains unchanged (Fe(II)) during the oxidative activation. ... 

In 2005 [61], Overman and coworkers described the application of their oxazoline system 41 to synthetically attractive trifluoroacetimidates 44 (Fig. 23) forming trifluoroacetamides 45, which, in contrast to benzamides 40, can be readily transferred into free primary allylic amines. 

Unfortunately, in the case of trifluoroacetimidates COP-Cl (46) still required catalyst loadings, which are not useful for large-scale applications [10 mol% Pd (II)], while long reaction times were necessary for high conversion. Moreover, the scope was limited to substrates bearing a-unbranched alkyl substituents R at the 3-position of the allylic imidate. 

Overman LE, Owen CE, Pavan MM, Richards CJ (2003) Catalytic asymmetric rearrangement of allylic N-aryl trifluoroacetimidates. A useful method for transforming prochiral allylic alcohols to chiral allylic amines. Org Lett 5 1809-1812... 

The synthesis of Cbz-protected D-valine methyl ester (296) (Scheme 40) begins with addition of an organometallic reagent to the ester function of 282. The resulting phosphonate 290 undergoes a Wittig reaction with isobutyraldehyde to afford 291. Chelation-controlled reduction of the ketone with zinc borohydride furnishes the a /-alcohol 292 (98% de). A [3,3] rearrangement of trifluoroacetimidate 293 produces allylic amine 294. Elaboration of the olefin to an ester furnishes the D-valine derivative 296 with 85% ee [101]. 

In the key reaction, a [3,3] rearrangement of trifluoroacetimidate 432 provides allylic amine 433 as a single diastereomer. After protecting-group adjustment, ozonolysis of the olefin, and oxidation of the aldehyde to acid, hydrolysis of all the protecting groups under acidic conditions furnishes the desired product [135]. The sole function of the lactic acid, whose carbon skeleton is removed by the ozonolysis, is to ensure the appropriate stereochemistry of the amino group. 

---