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Nucleophilic Trifluoromethylation of Carbonyl Compounds and Disulfides with Trifluoromethane and Silicon-Containing Bases

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journal contribution
posted on 07.12.2000, 00:00 by Sylvie Large, Nicolas Roques, Bernard R. Langlois
Provided that DMF (or another N,N-dialkylformamide) is present in the reaction medium, at least in a catalytic amount, fluoroform trifluoromethylates efficiently carbonyl compounds, even enolizable ones, when opposed to (TMS)2N- M+, generated in situ from N(TMS)3 and M+ F- or RO- Na+. When F- is used in a catalytic amount, silylated α-(trifluoromethyl)carbinols are obtained: in this case, the four-component system HCF3/N(TMS)3/catalytic F-/catalytic DMF behaves like the Ruppert's reagent, especially as far as nonenolizable carbonyl compounds are concerned (CF3SiMe3 remains more efficient for enolizable carbonyl compounds). This process involves an adduct between DMF and -CF3 which is the true trifluoromethylating agent. In the same way, fluoroform efficiently trifluoromethylates disulfides and diselenides when deprotonated with a strong base selected from t-BuOK or N(SiMe3)3/Me4NF (or TBAT). t-BuOK is more adapted to the trifluoromethylation of aryl disulfides whereas N(SiMe3)3/F- is well suited to that of aliphatic disulfides.