- Powerful, Thermally Stable, One-Pot-Preparable, and Recyclable Electrophilic Trifluoromethylating Agents: 2,8-Difluoro- and 2,3,7,8-Tetrafluoro-S-(trifluoromethyl)dibenzothiophenium Salts
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Although many electrophilic trifluoromethylating agents have been reported to date, practically useful reagents have yet to be developed. S-(Trifluoromethyl)dibenzothiophenium salts, known as Umemoto's reagents, have two significant drawbacks that have ha
- Umemoto, Teruo,Zhang, Bin,Zhu, Tianhao,Zhou, Xiaocong,Zhang, Peng,Hu, Song,Li, Yuanqiang
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- Benchmark and Solvent-Free preparation of sulfonium salt based electrophilic trifluoromethylating reagents
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Here we describe work devoted to the one-pot preparation of electrophilic trifluoromethylating reagents. The first part describes a reappraisal of our earlier experimental conditions and leads to an improved protocol that avoids the use of solvent: and allows better yields. The second part carefully studies the behavior of biaryl substrates, whose structures can drive the reaction through the formation of original noncyclic or tricyclic dibenzothiophenium salts. New compounds were tested, in a standard reaction with aniline, for their trifluoromethylating power and revealed equivalent or improved reactivity relative to that of existing reagents. Furthermore, contrary to common knowledge, the presence of electron-donating methyl groups gave reagents with very high activity. Wiley-VCH Verlag GmbH & Co, KGaA.
- Mace, Yohan,Raymondeau, Benoit,Pradet, Charlotte,Blazejewski, Jean-Claude,Magnier, Emmanuel
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experimental part
p. 1390 - 1397
(2009/08/07)
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- Effective methods for preparing S-(trifluoromethyl)dibenzothiophenium salts
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New effective methods were developed for the preparation of useful electrophilic trifluoromethylating agents, S-(trifluoromethyl)dibenzothiophenium tetrafluoroborate (3) and triflate (4) and S-(trifluoromethyl)dibenzothiophenium-3-sulfonate (6). Thus, salts 3 and 4 were produced by the intramolecular cyclization of sulfoxide 1 with fuming sulfuric acid, followed by the counteranion replacement reaction of the intermediate (2) with sodium tetrafluoroborate and triflate, and salt 6 was directly produced from 1 by treatment with excess fuming sulfuric acid. Useful preparative methods for 1 were also described.
- Umemoto, Teruo,Ishihara, Sumi
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- Effective methods for preparing S-(trifluoromethyl)dibenzothiophenium salts
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New effective methods were developed for the preparation of useful electrophilic trifluoromethylating agents, S-(trifluoromethyl)dibenzothiophenium tetrafluoroborate (3) and triflate (4) and S-(trifluoromethyl)dibenzothiophenium-3-sulfonate (6). Thus, salts 3 and 4 were produced by the intramolecular cyclization of sulfoxide 1 with fuming sulfuric acid, followed by the counteranion replacement reaction of the intermediate (2) with sodium tetrafluoroborate and triflate, and salt 6 was directly produced from 1 by treatment with excess fuming sulfuric acid. Useful preparative methods for 1 were also described.
- Umemoto, Teruo,Ishihara, Sumi
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p. 181 - 187
(2007/10/03)
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- Power-variable electrophilic trifluoromethylating agents. S-, Se-, and Te-(trifluoromethyl)dibenzothio-, -seleno-, and -tellurophenium salt system
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S-, Se-, and Te-trifluoromethylated dibenzoheterocyclic onium salts, their derivatives, and related salts were synthesized by the direct fluorination of a mixture of 2-[(trifluoromethyl)thio- or seleno]biphenyls and triflic acid (TfOH) or HBF4 etherate, by treatment of the corresponding sulfoxides and selenoxides with Tf2O, by a new type of tellurium activation of 2-[(trifluoromethyl)telluro]biphenyl with Tf2O and (CH3)2SO, or by derivation from the onium salts obtained. Examination of reactivity indicated the trifluoromethyl heterocyclic salts to be greatly reactive compared to nonheterocyclic salts and indicated that this heterocyclic salt system serves as a source of widely applicable trifluoromethylating agents. Their capacity to function as such varied remarkably and increased in the order of Te 2 2. For mixed heterocyclic salts, the orders differed, apparently being determined by the electron deficiency of the CF3 group due to the electron-withdrawing or -donating effects of chalcogens and ring substituents, rather than the inherent nature of the chalcogens. Because of this variation, it was possible to trifluoromethylate a wide range of nucleophilic substrates differing in reactivity: carbanions, activated aromatics, heteroaromatics, enol silyl ethers, enamines, phosphines, thiolate anions, and iodide anions. The reaction mechanism is discussed, and a bimolecular ionic substitution mechanism competing with a free CF3 radical chain mechanism is proposed. Thus, a new field, electrophilic trifluoromethylation, has been established by the present study.
- Umemoto, Teruo,Ishihara, Sumi
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p. 2156 - 2164
(2007/10/02)
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- Power-variable trifluoromethylating agents, (trifluoromethyl)dibenzothio- and -selenophenium salt system
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(Trifluoromethyl)dibenzothio- and -selenophenium triflates and their nitro derivatives differing in trifluoromethylating power were developed as a new system of electrophilic trifluoromethylating agents.
- Umemoto,Ishihara
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p. 3579 - 3582
(2007/10/02)
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