Pentafluorophenyl trifluoroacetate

FIGURE 7.13 Preparation of an Fmoc-amino-acid pentafluorophenyl ester by reaction of the acid with pentafluorophenyl trifluoroacetate in the presence of pyridine.32... 

The alternative method for making activated esters is base-catalyzed transesterification. Fmoc-amino acids are esterified in excellent yields by reaction with pentafluorophenyl trifluoroacetate at 40°C in the presence of pyridine (Figure 7.13). A mixed anhydride is formed initially, and the anhydride is then attacked by the pentafluorophenoxy anion that is generated by the pyridine. Succinimido, chlorophe-nyl, and nitrophenyl esters were made by this method when it was introduced decades ago. A unique variant of this approach is the use of mixed carbonates that contain an isopropenyl group [Cf C CfyO-COjR]. These react with hydroxy compounds in the presence of triethylamine or 4-dimethylaminopyridine (see Section 4.19) to give the esters and acetone.30 35... 

M Green, J Berman. Preparation of pentafluorophenyl esters of Fmoc protected amino acids with pentafluorophenyl trifluoroacetate. Tetrahedron Lett 31, 5851, 1990. 

Fig. 13. Acylation via activation of a resin-bound carboxylic acid, (a) Pentafluorophenyl trifluoroacetate (6 equiv.) in Py/DMF (1 10), 1 h (b) amine (6 equiv.) CH2C12/DMF (c) TFA/ DCM (1 1) 1 h.

In a related approach, pentafluorophenyl esters of Fmoc amino acids 61 (see Table 14) were prepared from a mixture of acid 59 and pentafluorophenyl trifluoroacetate in dimeth-ylformamide in the presence of pyridine,which is a transesterification method developed by Sakakibara (Scheme The reaction involves formation of mixed carboxylic acid... 

There is a newer alternative method of synthesizing Fmoc-protected pentafluorophenyl ester amino acids employing pentafluorophenyl trifluoroacetate (3). ... 

Recently a high-yield synthesis of a 2 -deoxy-0 -(pentafluorophenyl)guanosine derivative 11 has been reported by reaction of deoxyguanosine with trifluoroacetic anhydride in pyridine, followed by treatment with pentafluorophenol. ... 

Single-crystal X-ray structures have been reported for the following aryl- and heteroaryliodo-nium salts diphenyliodonium triiodide [412], (2-methylphenyl)(2-methoxyphenyl)iodonium chloride [413], (2-methoxy-5-methylphenyl)(4-methoxy-2-methylphenyl)iodonium trifluoroacetate [414], (2-methoxy-5-methylphenyl)(4-methoxyphenyl)iodonium trifluoroacetate [415], a complex of diphenyliodonium tetrafluoroborate with pyridine [416], a complex of diphenyliodonium tetrafluoroborate with 1,10-phenanthroline [417], a complex of diphenyliodonium tetrafluoroborate with 18-crown-6 [418], 1-naphthylphenyliodonium tetrafluoroborate [419], 3,10-dimethyl-10//-dibenzo[, e]iodinium tetrafluoroborate [420], aryl(pentafluorophenyl)iodonium tetrafluoroborates [421], 4,4 -[bis(phenyliodonium)]-diphenylmethane ditriflate [422], [bis(4-methoxyphenyl)](diethylaminocarbodithioato)iodine(in) [423], di(p-tolyl)iodonium bromide [424], diphenyliodonium chloride, bromide and iodide [425,426], diphenyliodonium nitrate [427], diphenyliodonium tetrafluoroborate [428], thienyl(phenyl)iodonium salts [401], (anft-dimethanoanthracenyl)phenyliodonium tosylate and hexafluorophosphate [429] and 3-mesityl-5-phenylisoxazol-4-yl(phenyl)iodonium p-toluenesulfonate [409]. 

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