Preparation of and Fluoroalkylation with (Chlorodifluoromethyl)trimethylsilane, Difluorobis(trimethylsilyl)methane, and 1,1,2,2-Tetrafluoro-1,2-bis(trimethylsilyl)ethane
摘要:
CF2BrCl reacts with aluminum/N-methylpyrrolidinone in the presence of chlorotrimethylsilane to give Me(3)SiCF(2)Cl in high yield. Similarly, CF2Br2 gives Me(3)SiCF(2)Br with bromotrimethylsilane. Chlorodifluoromethylation of aldehydes using Me(3)SiCF(2)Cl and a catalytic amount of TBAF in polar solvents occurs at room temperature, providing difluoromethylated alcohols in two steps. Electroreduction of Me(3)SiCF(2)Cl in the presence of chlorotrimethylsilane gives Me(3)SiCF(2)SiMe(3) (anion-derived product) and Me(3)SiCF(2)CF(2)SiMe(3) (radical-derived product). Using THF/HMPA strongly favors the former, whereas THF/TDA-1 (tris(3,6-dioxaheptyl)amine) the latter. Me(3)SiCF(2)-SiMe(3) difluoromethylates aldehydes acting as a difluoromethylene dianion (''CF22-'' equivalent), whereas Me(3)SiCF(2)-CF(2)SiMe(3) acts at room temperature as an in situ source for the perfluorovinyl anion (due to beta-elimination of fluorotrimethylsilane). However, at low temperature the elimination pathway is suppressed and tetrafluoroethylene dianion (''-CF2CF2-'' equivalent) behavior is observed, The structure of Me(3)SiCF(2)CF(2)SiMe(3) 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).
Preparation of Tri- and Difluoromethylsilanes via an Unusual Magnesium Metal-Mediated Reductive Tri- and Difluoromethylation of Chlorosilanes Using Tri- and Difluoromethyl Sulfides, Sulfoxides, and Sulfones
作者:G. K. Surya Prakash、Jinbo Hu、George A. Olah
DOI:10.1021/jo030110z
日期:2003.5.1
A new and efficient method for the preparation of tri- and difluoromethylsilanes using magnesium metal-mediated reductive tri- and difluoromethylation of chlorosilanes is reported using tri- and difluoromethyl sulfides, sulfoxides, and sulfones. The byproduct of the process is diphenyl disulfide. Since phenyl trifluoromethyl sulfone, sulfoxide, and sulfide are readily prepared from trifluoromethane