1,2-Bis(dimethylphenylsilyl)tetrafluoroethane. Application to the Trifluorovinylation and Tetrafluoroethylenation of Carbonyl Compounds
作者:Toshiki Hagiwara、Takamasa Fuchikami
DOI:10.1246/cl.1997.787
日期:1997.8
The reaction of 1,2-bis(dimethylphenylsilyl)tetrafluoroethane with a small excess of benzaldehyde in the presence of the promoter gave the trifluorovinylated product, 1,1,2-trifluoro-3-phenylpropen-3-ol, selectively. The tetrafluoroethylenated product, 2,2,3,3-tetrafluoro-1,4-diphenylbutane-1,4-diol, was also obtained in benzaldehyde solvent or at low temperatures.
rearrangement reaction gave the alcohols with perfect (E)*-selection over the newly created olefin bond for two substrates. Lipase-catalyzed optical resolution of 4,4,5-trifluoroalk-1,5-dien-3-ols was successfully performed to afford opticallyactive partly gem-difluorinated allylic alcohols for the first time.
Preparation of and Fluoroalkylation with (Chlorodifluoromethyl)trimethylsilane, Difluorobis(trimethylsilyl)methane, and 1,1,2,2-Tetrafluoro-1,2-bis(trimethylsilyl)ethane
作者:Andrei K. Yudin、G. K. Surya Prakash、Denis Deffieux、Michael Bradley、Robert Bau、George A. Olah
DOI:10.1021/ja962990n
日期:1997.2.1
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).