enantioselective trifluoromethylsulfenylation employing
N-trifluoromethylthiophthalimide as the electrophilic CF3S-
source; however, the preparation of this reagent involves
the extremely toxic and corrosive trifluoromethylsulfenyl
chloride.16
Scheme 1
Figure 1. Examples of CF3S-containing products.
Billard et al. prepared a family of trifluoromethanesul-
fanamides, which could be used as electrophilic CF3Sꢀ
sources capable of reacting efficiently with various orga-
nometallic alkenyl and alkynyl reagents.11 The group of
Daugulis described a trifluoromethylthiolation process
based on copper(II) acetate and bis(trifluoromethyl)
disulfide;12 however, the latter component is highly toxic,
expensive, and not easy to handle (bp 34ꢀ35 °C). Shen
and Lu also prepared a hypervalent iodine reagent for the
direct electrophilic trifluoromethylthiolation under mild
conditions. The limitations of this reagent are that it is only
stable for a few days in solution at rt and requires AgSCF3
as the precursor.13 Huang and Weng introduced a complex
CuSCF3 reagent, [(bpy)Cu(SCF3)], which reacts with a
wide range of aryl and heteroaryl halides to produce aryl
trifluoromethylthioethers in good yield.14 This and other
related complexes have been claimed to be stable in the
solid state to storage under air for several days. Recently,
Shibata and his team developed a trifluoromethanesulfonyl
hypervalent iodonium ylide as a novel electrophilic-
type trifluoromethylthiolation reagent allowing the intro-
duction of the CF3S- group into various nucleophiles.15
Most recently, Rueping and collaborators developed an
In contrast to most of the methods adumbrated above,
we now describe an efficient, cheap, air-stable, and easily
available metal-free reagent allowing the generation
and direct capture of the trifluoromethylthiolate anion.
A few years ago, we described the preparation and use of
S-trifluoromethyl xanthate 3a, which proved to be a con-
venient source of trifluoromethyl radicals.17 In principle,
this xanthate could also act as a precursor for trifluoro-
methanethiol or its salts through ionic hydrolysis or ami-
nolysis. While the synthesis of xanthate 3a outlined in
Scheme 1 and starting from xanthate salt 1a is relatively
straightforward, the yield is somewhat modest (38%). The
main difficulty is the high sensitivity of the intermediate
S-trifluoroacetyl xanthate 2a toward water or nucleophiles
in general. In fact, we have shown that S-acyl xanthates in
general can be decomposed catalytically by an ionic chain
mechanism, so even a small amount of a nucleophilic
impurity can have a serious impact on the yield.18 Hence,
we considered modifying reagent 3a by replacing the
phenethyl group with a more lipophilic n-octadecanoyl
chain. Indeed, the yield of corresponding S-trifluoro-
methylxanthate 3bstartingfrom xanthate salt1bincreased
to61%, and the reaction could beperformedonmultigram
scale (approximately 10 g of 3b were prepared in a
single run). In this process, visible light from a tungsten
incandescent lamp was used to trigger the radical chain
decarbonylation sequence, in preference to a chemical
initiator such as lauroyl peroxide, in order to avoid com-
plications during purification caused by the highly
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