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Togni reagent II

Chemical compound From Wikipedia, the free encyclopedia

Togni reagent II
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Togni reagent II (1-trifluoromethyl-1,2-benziodoxol-3(1H)-one) is a chemical compound used in organic synthesis for direct electrophilic trifluoromethylation.[1][2]

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History

Synthesis, properties, and reactivity of the compound were first described in 2006 by Antonio Togni and his coworkers at ETH Zurich.[3] The article also contains information on Togni reagent I (1,3-dihydro-3,3-dimethyl-1-(trifluoromethyl)-1,2-benziodoxole).

Preparation

The synthesis consists of three steps. In the first step, 2-iodobenzoic acid is oxidized by sodium periodate and cyclized to 1-hydroxy-1,2-benziodoxol-3(1H)-one. The target compound can then be obtained by acylation with acetic anhydride and subsequent substitution reaction with trifluoromethyltrimethylsilane.[4]

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Alternatively, trichloroisocyanuric acid can be used as oxidant in the place of sodium periodate for a newer one-pot synthesis method.[5]

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Properties

Physical properties

The compound crystallized in a monoclinic crystal structure. The space group is P21/n with four molecules in the unit cell.[3] From the crystallographic data, a density of 2.365 g·cm−3  was deduced.[3]

Chemical properties

Pure Togni reagent II is metastable at room temperature. Heating it above the melting point will lead to strong exothermic decomposition, in which trifluoroiodomethane (CF3I) is released.[4] The heat of composition at a temperature of 149 °C and higher has been determined to be 502 J·g−1.[6] From recrystallization in acetonitrile, small amounts of trifluoromethyl-2-iodobenzoate and 2-iodobenzyl fluoride were observed as decomposition products.[4] Togni reagent II reacts violently with strong bases and acids, as well as reductants.[4] In tetrahydrofuran, the compound polymerizes.[4]

Uses

Togni reagent II is used for trifluoromethylation of organic compounds. For phenolates, the substitution takes place preferably in the ortho position. It is possible to obtain a second substitution by using an excess of Togni reagent II.[7]

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Reactions with alcohols yield the corresponding trifluoromethyl ethers.[8]

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Trifluoromethylation of alkenes is possible under copper catalysis.[9]

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References

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