Sumi Ishihara

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.

Electrophilic fluorination with N,N′-difluoro-2,2′-bipyridinium salt and elemental fluorine

Abstract N,N′ -Difluoro-2,2′-bipyridinium bis(tetrafluoroborate) (MEC-31) was shown to be a highly reactive electrophilic fluorinating agent with the highest effective fluorine content in its class. We have developed the perfect recycled fluorination system with MEC-31 for the lower-cost industrial fluorination and for an environment. MEC-31 can be completely recycled including the counter-anion. We found the fluorination of 2-naphthol in liquid CO 2 with MEC-31 in the presence of catalytic amount of NaOTf proceeded quantitatively without the generation of by-product. In the fluorination of 1,3-dicarbonyl compounds with elemental fluorine, we found the introduction method of fluorine gas would be very important in order to make a reaction efficient. As fluorination goes on, the quantity of 1,3-dicarbonyl compounds of the starting material is reduced gradually, and therefore the quantity of fluorine must be reduced by the method to control the flow rate or the concentration of fluorine gas diluted with nitrogen, together the fluorination to proceed efficiently.

Power-variable trifluoromethylating agents, (trifluoromethyl)dibenzothio- and -selenophenium salt system

Abstract Although it should be a significant strategy for introducing a trifluoromethyl group into an organic compound, electrophilic trifluoromethylation has not been developed so far. The reason for this would be the lack of a good electrophlic reagent. We have synthesized (trifluoromethyl)dibenzothio- and -selenophenium salts 1-5 as a new system of trifluoromethylating agents, power-variable electrophilic trifluoromethylating agents. The trifluoromethylation power order is 2