Triflyl chloride

Section V contains specific examples of procedures for Inflate synthesis some general comment about these procedures is worthwhile. Triflic anhydride is the reagent of choice for preparing triflates derived from sugars, whereas triflyl chloride is used more often when uucleosides are involved. Triflate formation with triflic anhydride requires addition of a base (usually pyridine) to the reaction mixture to neutralize the triflic acid produced [Eq. (4) 7]. Some triflates are reactive enough that pyridine can function as a nucleophile in the substitution process. In these instances, replacement of pyridine with a non-nucleophilic base, such as 2,6-di-r-butyl-4-methylpyridine, avoids this undesired reaction (Scheme 1) [7]. 

Scheme 2 Triflate formation with triflyl chloride.

B.. Synthesis of a triflate ester with triflyl chloride 97... 

Fig. 13. Formation of triflyl chloride by oxidative chlorination of benzyltrifluoromethylsulfide...

Anhydronucleosides of pyrazolo[3,4-rf]pyrimidines have been prepared by 2, 3 -rra/i5-elimination of the corresponding xylofuranosyl systems. When the a-hydroxyphosphonate 16 (see Vol. 29, p. 291 and earlier) was desilylated and then treated with triflyl chloride, the epoxyphosphonate 17 was obtained, and a 2, 3 -epoxy-2 -phosphonate was made similarly. ... 

Triflyl chloride was also used for the preparation of fluoroalkyl trifluoromethanesulfonates that act as highly efficient fluoroalky-lating reagents, 10 times more reactive than the corresponding tosylates. Significant formation of fluoroalkyl ether side-products was observed when trifluoromethanesulfonyl fluoride was used. Fluoroalkyl p-nitrophenyl ethers were thus prepared in high yields, without side-elimination reactions (eq 7). ... 

Other nitrogen nucleophiles can react efficiently with triflyl chloride. Below —30°C, 1,1-dimethylhydrazine was sulfonated to afford the corresponding trifluoromethanesulfonic hydrazide. In the azole series, the side chain of some 1,2,3-triazoles was functionalized with a trifluoromethanesulfonyl group (eq 10). When pentafluoroethanesulfonyl chloride was used in this transformation, a mixture of mono- and di-sulfonylated derivatives was... 

Some polysulfanes have also been reacted with triflyl chloride. In particular, iron sulfanes of the type ()u.-Sjc)[CpFe(CO)2]2 were converted into thiosulfonato complexes to study the mechanism of sulfur-sulfur bond formation during the Claus process. 

Chlorination of Activated Methylene Groups. Triflyl chloride was used for the high yielding chlorination of carbon acids, and this reaction was applied to the synthesis of simple 2,2-disubstituted heterocycles. This method has been extended to the preparation of heterocycles fused with -lactams. Treatment of a hydroxyphenylazetidinone with triflyl chloride and triethy-lamine afforded a hemiaminal in 90% yield, through the chlorination of the dibenzyl malonate moiety (eq 11). Performing the same transformation on a mercapto- -lactam precursor led to the formation of a sulfenyl chloride intermediate rather than to chlorination of the malonate moiety. ... 

Synthesis of Tetraarylporphyrins. Triflyl chloride was used under aerobic oxidation conditions to produce tetraarylporphyrins from pyrrole and various aromatic aldehydes. The reaction proceeds through condensation of pyrrole to the aromatic aldehyde to form an intermediate aryl triflate which then undergoes polymerization and cyclization of the tetrapyrrolic oligomer. Air oxidation of the porphyrinogen intermediate completes the sequence (eq 15). 

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