Trifluoroacetimidates

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. 

Fig. 23 Asymmetric tizti-Claisen rearrangement of trifluoroacetimidates using precatalyst 41...

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. 

Fig. 26 Asymmetric aza-Claisen rearrangement of trifluoroacetimidates 49 generating iV-substi-tuted quaternary stereocenters...

Fig. 30 Asymmetric aza-Claisen rearrangement of (Z)-configured trifluoroacetimidates 44 3.1.2 Bispalladium-Catalyzed Michael-Addition of a-Cyanoacetates...

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... 

Prasad RS, Anderson CE, Richards CJ, Overman LE (2005) Synthesis of tert-leucine-derived cobalt oxazoline palladacycles. Reversal of palladation diastereoselectivlty and application to the asymmetric rearrangement of N-aryl trifluoroacetimidates. Organometallics 24 77-81... 

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... 

Xin ZQ, Fischer DF, Peters R (2008) Catalytic asymmetric formation of secondary allylic amines by Aza-Claisen rearrangement of trifluoroacetimidates. Synlett 1495-1499... 

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. 

In 1983, Schmidt reported another type of glycosyl imidates, trifluoroacetimidates... 

This review covers the recent advances in the use of O-glycosyl imidates in oligosaccharide and glycoconjugate synthesis, with emphasis on literature published between 1999 and 2006. However, because of the large volume of work in this area, only the most representative applications will be presented. One can refer to the similar preceding review [381] published in 2000 and another quite comprehensive review [375] on trichloroacetimidate method published in 1994 for earlier application of glycosyl trichloroacetimidates. Trifluoroacetimidate method will be discussed separately in this review in the light of its less popularity in carbohydrate chemistry. 

Trifluoroacetimidates show similar reactivity.178 Imidate rearrangements are catalyzed by palladium salts.179 The mechanism is presumably similar to that for the Cope rearrangement (see p. 382). 

The trifluoroacetimidate Claisen rearrangement has been successfully applied to several natural product syntheses in which excellent chiral transfer has been achieved, as illustrated in the conversion of 8 into 9.58 Although this methodology is designed to synthesize fluorine-free amines, it does illustrate the advantages that fluorine can often offer in tuning synthetic techniques. 

The diaryl tellurium carboximides may exist in syn- and anti-forms if the N —C bond has double-bond character. The syrt-forms are stabilized by the proximity of opposite charges on the tellurium atom and the oxygen atom. Most of the diaryl tellurium trifluoroacet-imides only exist in the sy -form2. However, bis[4-methoxyphenyl] tellurium trifluoroacetimide was isolated in both forms. When the crude reaction product was dissolved in hot benzene and the resulting solution was cooled to and kept at 10°, cubic crystals of the antiform (m.p. 169°) precipitated. Addition of hexane to the hot filtrate precipitated the syn-form as an oil that crystallized on trituration with diethyl ether. The jy -form melted at 81°2. 

Diaryl tellurium trifluoroacetimides and sulfonimides react with l,3-dioxo-5,5-dimeth-ylcyclohexane in chloroform at 20° to produce diaryl 2,6-dioxo-4,4-dimethyl-cyclohexyl-idene telluriums3. 

Diaryl tellurium trifluoroacetimides and 4-methylbenzenesulfonimides transferred the imide group to triphenylphosphine2. 

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