Trifluoroacetimidate activation

Weiss ME, Fischer DF, Xin ZQ, Jautze S, Schweizer WB, Peters R (2006) Practical, highly active, and enantioselective ferrocenyl-imidazoline palladacycle catalysts (FIPs) for the Aza-Claisen rearrangement of A-para-methoxyphenyl trifluoroacetimidates. Angew Chem Int Ed 45 5694-5698... 

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... 

Disarmed glycosyl trichloro- and /V-(phenyI)trifluoroacetimidates were efficiently activated by the system I2/Et3SiH for the rapid and high-yield glycosylation of primary and secondary saccharide acceptors, and it was observed that the presence of AW 4 A MS was decisive for achieving high reaction yields.62... 

M. Adinolfi, B. Gaspare, A. Iadonisi, and M. Schiattarella, Iodine/triethylsilane as a convenient promoter system for the activation of disarmed glycosyl tri-chloro- and /V-(phenyl)trifluoroacetimidates, Synlett, 2 (2002) 269-270. 

M. Adinolfi, A. Iadonisi, A. Ravida, and M. Schiattarella, Versatile use of ytterbium(III) triflate and acid washed molecular sieves in the activation of glycosyl trifluoroacetimidate donors. Assemblage of a biologically relevant tetrasaccharide sequence of Globo H, J. Org. Chem., 70 (2005) 5316-5319. 

Iadonisi and coworkers developed a clever block-synthesis approach to the antitumor a-(l >3)-pentamannan known as PI-88, illustrating the selective activation of a trichloroacetimidate 43 in the presence of a /V-phenyl trifluoroacetimidate 44 (Scheme 10).12 This useful selectivity enabled assembly of the complete pentasaccharide with the adjustment of only a single protecting group in the course of the entire sequence. 

With a cyclopalladated (ti -tetraphenylcyclobutadiene)cobalt oxazoline propyl chloro-bridged compound 8.17 and a trifluoroacetate-bridged compound 8.20 as catalysts, moreover, the rearrangement of A-(4-methoxyphenyl)trifluoroacetimidate 8.13 [17], aUyUc trichloroacetimidate 8.15 [18], and A-(4-methoxyphenyl)trifluoro-acetimidate 8.18 [19] to the corresponding amides (8.14, 8.16, 8.19) proceeds in high yields and high enantiomeric purities without use of a silver salt as an activator, as shown in Eqs. (8.2), (8.3), and (8.4), respectively. 

Eventually, heptose trichloroacetimidate 129, activated by catalytic TMSOTf, proved to be superior for this glycosylation. The more reactive disaccharide N-phenyl trifluoroacetimidate 135 was then coupled with disaccharide 131 upon TMSOTf activation to give the desired a-linked tetrasaccharide 136 in a satisfactory yield of 72% (Scheme 2.29). 

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. ... 

---