Fluorierte Elementorganika

Deoxygenative gem-difluoroolefination of carbonyl compounds with (chlorodifluoromethyl)trimethylsilane and triphenylphosphine

“…(Halodifluoromethyl)trimethylsilanes including TMSCF 3 (Ruppert–Prakash reagent), TMSCF 2 Cl, and TMSCF 2 Br are initially prepared by reductive silylation of ozone-depleting-substances bromotrifluoromethane (CF 3 Br) [ 35 ], bromochlorodifluoromethane (CF 2 BrCl) [ 36 – 37 ], and dibromodifluoromethane (CF 2 Br 2 ) [ 36 – 37 ] with chlorotrimethylsilane (TMSCl). In recent years, Prakash and co-workers have discovered two Freon-free methods for the synthesis of TMSCF 3 from fluoroform (CF 3 H), which paved the way for the synthetic applications of TMSCF 3 [ 38 – 39 ].…”

“…When a 1:10 mixture of TMSCF 2 Br and TMSCl was heated in neat in the presence of 5 mol % of tetrabutylammonium chloride (TBAC) for 2 hours, 19 F NMR spectroscopy analysis showed that the ratio of TMSCF 2 Cl to TMSCF 2 Br was 2.3:1, and prolonging reaction time could not improve the ratio. In view of the difficulty in separating TMSCF 2 Cl from the reaction mixture because of the approximate boiling points of TMSCF 2 Cl (~85 °C) [ 36 – 37 ] and TMSCF 2 Br (~105 °C) [ 36 – 37 ], other chloride sources were tried to achieve a full conversion of TMSCF 2 Br. Gratifyingly, when the reaction was performed in benzonitrile (bp ~190 °C) at 80 °C using a slight excess of silver chloride under the catalysis of TBAC, a full conversion of TMSCF 2 Br afforded TMSCF 2 Cl in 54% yield.…”

ChemInform Abstract: Synthesis of gem‐Difluorocyclopropa(e)nes O‐, S‐, N‐, and P‐Difluoromethylated Compounds with TMSCF2Br.

“…[22c,d] However, the reactions suffer from disadvantages such as high temperatures or large excess of reagent. Although TMSCF 2 Cl is arguably one of the most versatile difluorocarbene reagents, [23] its preparation from ozone-depleting BrCF 2 Cl [24] makes its wide application less attractive. Therefore, the development of an operationally simple and environmentally benign difluorocarbene precursor which is effective with a broad substrate scope under relatively mild conditions is highly desirable.…”

Synthesis of gem‐Difluorocyclopropa(e)nes and O‐, S‐, N‐, and P‐Difluoromethylated Compounds with TMSCF2Br

“…However, the reactions suffer from disadvantages such as high temperatures or large excess of reagent. Although TMSCF 2 Cl is arguably one of the most versatile difluorocarbene reagents,23 its preparation from ozone‐depleting BrCF 2 Cl24 makes its wide application less attractive. Therefore, the development of an operationally simple and environmentally benign difluorocarbene precursor which is effective with a broad substrate scope under relatively mild conditions is highly desirable.…”