Teruo Umemoto

Useful electrophilic trifluoromethylating agents; S-, Se- and Te-(trifluoromethyl)dibenzo-thio-, -seleno- and -telluro-phenium-3-sulfonates

Abstract Se, Se- and Te -(Trifluoromethyl)dibenzo-thio-. -seleno- and -telluro-phenium-3-sulfonates and their dimethyl and nitro derivatives have been synthesized in good yield by sulfonation of the corresponding (trifluoromethyl) dibenzocyclic chalcogen salts with fuming sulfuric acid or by sulfonation followed by nitration. The practical use of these power-variable trifluoromethylating agents has been demonstrated. Thus, they provide good yields of trifluoromethylated products, and the by-product (a salt of dibenzothiophene-3-sulfonic acid or an analog) was easily removed from the products by filtration or by washing with water. S -(Perfluoro-ethyl, -n-butyl- and -n-octyl) dibenzothiophenium-3-sulfonates have also been synthesized and a similar perfluoroalkylation using one of them has been accomplished.

EFFECTIVE METHODS FOR PREPARING S-(TRIFLUOROMETHYL)DIBENZOTHIOPHENIUM SALTS

Abstract 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.

Kinetic study of trifluoromethylation with s-(trifluoromethyl) dibenzothiophenium salts

Abstract The kinetic parameters were determined for C-trifluoromethylation of aniline with S-(trifluoromethyl)dibenzothiophenium triflate (1), its 3,7-dinitro derivative (2) and S-(trifluoromethyl)diphenylsulfonium triflate (3) in DMF-d7. The higher reactivity of heterocyclic 1 compared with non-heterocyclic 3 could be explained on the basis of its greatly enhanced activation entropy (ΔS≠: −11.2 cal mol −1 K−1 for 1; −47.1 for 3), but not its enhanced activation enthalpy (ΔH≠: 21.2 kcal mol−1 for 1; 12.1 for 3). The aromatic delocalization of the heterocyclic ring may thus be only slightly disturbed by the S-trifluoromethyl substituent. The high reactivity of 2 was attributed to the great electron deficiency caused by two nitro groups in addition to the heterocyclic salt system (ΔH≠ 17.0 kcal mol−1, ΔS≠ −9.1 cal mol−1 K−1 for 2). The reaction mechanism is discussed; the conventional SN2 attack mechanism was ruled out and a mechanism for a side-on attack to the CF3-S bond may possibly be applicable.

Twenty years in my fluorine chemistry

Abstract Dr. Umemoto’s research is briefly described and his achievements are chronologically summarized, which include electrophilic perfluoroalkylating agents (FITS), N -fluoropyridinium salts as power and structure-variable electrophilic fluorinating agents and application to battery materials, and O -, S -, Se -, and Te - trifluoromethyled dibenzoheterocyclic onium salts as power-variable electrophilic trifluoromethylating agents.

Controlled selective fluorination with N-fluoropyridinium salt system

Abstract Controlled selective fluorination should be of great importance in preparing desired fluoroorganic molecules. We have developed N - fluoropyridinium salts as power and structure-variable fluorinating agents. In these studies, we found that counteranion part of the N -fluoropyridinium salts functions considerably in selective fluorination. This talk will discuss about the synthesis of a series of counteranion-bound N -fluoropyridinium salts and controlled selective fluorination with them.

Structural studies of novel trifluoromethylating agents—(trifluromethyl)dibenzothio- and -selenophenium salt system

Abstract (Trifluoromethyl)dibenzothio- and -selenophenium salts and their nitro derivatives 1–5 were found to serve as power-variable electrophilic trifluoromethylating agents. It would be of great significance to investigate how the power-variableness or the reaction mechanism relate to the stereostructure of the reagents. Hence, the structures of the series of the reagents are studied X-ray crystallographically. Crystals 1 and 2 belong to monoclinic system with a space group of P2 1 /n. One of the most characteristic found in their structures is that the trifluoromethyl group is protruded from the plane of the heterocyclic ring almost perpendicularly as is shown below. Other related salts will be included in the discussion.