Preparation of and fluoroalkylation with (chlorodifluoromethyl)trimethylsilane, difluorobis(trimethylsilyl)methane, and 1,1,2,2-tetrafluoro-1,2-bis(trimethylsilyl)ethane

Abstract

CF2BrCl reacts with aluminum/N-methylpyrrolidinone in the presence of chlorotrimethylsilane to give Me3SiCF2Cl in high yield. Similarly, CF2Br2 gives Me3SiCF2Br with bromotrimethylsilane. Chlorodifluoromethylation of aldehydes using Me3SiCF2Cl and a catalytic amount of TBAF in polar solvents occurs at room temperature, providing difluoromethylated alcohols in two steps. Electroreduction of Me3SiCF2Cl in the presence of chlorotrimethylsilane gives Me3SiCF2SiMe3 (anion-derived product) and Me3SiCF2CF2SiMe3 (radical-derived product). Using THF/HMPA strongly favors the former, whereas THF/TDA-1 (tris(3,6-dioxaheptyl)amine) the latter. Me3SiCF2SiMe3 difluoromethylates aldehydes acting as a difluoromethylene dianion ('CF22-'/equivalent), whereas Me3SiCF2CF2SiMe3 acts at room temperature as an in situ source for the perfluorovinyl anion (due to β-elimination of fluorotrimethylsilane). However, at low temperature the elimination pathway is suppressed and tetrafluoroethylene dianion ('-CF2CF2-'/equivalent) behavior is observed. The structure of Me3SiCF2CF2SiMe3 was analyzed by X-ray diffraction. All of the studied fluoroalkylating reagents are moisture- and air-stable and can be readily obtained from a single convenient precursor (CF2BrCl).