Synthesis of difluoroenoxysilanes from acylsilanes and trifluoromethyltrimethylsilane (TFMTMS). Dramatic effect of the catalytic fluoride source

Acyl Silanes

“…Elimination of fluoride ion then occurs to give 1-silyloxy-2,2-difluoroalkenes (silyl enol ethers of difluoromethyl ketones) 220,221 . The same type of intermediates and subsequent reaction are of course seen in the addition of trifluoromethyl anion to alkanoyl silanes (vide supra, Section IV.A.1) 188 . The reaction was applied to a synthesis of a fluorinated brassinosteroid.…”

“…The reaction, which proceeds through addition, Brook rearrangement and cyclization, is also successful with ,ˇ-unsaturated acyl silanes (vide infra, Section IV.D) 187 Fluoride ion-catalysed addition of trifluoromethyltrimethylsilane to acyl silanes occurs to give 1,1-difluoro-2-trimethylsilyloxyalkenes (silyl enol ethers of difluoromethyl ketones), through nucleophilic addition of trifluoromethyl anion, Brook rearrangement and loss of fluoride. These compounds could be isolated when tetrabutylammonium difluorotriphenylstannate was used as a catalyst; use of tetrabutylammonium fluoride gave the product corresponding to subsequent aldol reaction with the difluoromethyl ketone (Scheme 78) 188 A Japanese group have reported an unusual reaction, mediated by lanthanide metals, involving the deoxygenative acylation of diaryl ketones with aryl acyl silanes, to give 1,1-diaryl acetophenones (Scheme 79) 189 .…”

Preparation of 1-aryl-2,2-difluoro enol esters via dehydrosulfonylation of α-(phenylsulfonyl)difluoromethylated benzoates

“…More recently, a novel C-F bond cleavage chemistry with trifluoromethyl compounds has been developed by Uneyama and co-workers, which significantly expanded both the preparation and the synthetic applications of 2,2-difluoro enol building blocks [5,9]. However, compared to the 2,2-difluoro enol silyl ethers, 2,2-difluoro enol carboxylic esters are less explored [6,8]. We envision that 2,2-difluoro enol esters can be relatively more stable than 2,2-difluoro enol silyl ethers [10], and such class of compounds can be used as interesting fluorinated building blocks for many applications.…”

“…Initially, 2,2-difluoro enol silyl ethers were prepared from chlorodifluoromethyl ketones [6] or from acyltrifluoromethylsilane through Brook rearrangement [7,8]. Trifluoroethanol has been widely used as an inexpensive starting material for prepation of 2,2-difluoro enol derivatives [4].…”

Reactions of Difluoroenoxysilanes with Glycosyl Donors: Synthesis of Difluoro-C-glycosides and Difluoro-C-disaccharides

“…The possibility to carry out the reaction in methylene chloride as the ideal solvent for Lewis acid activation of electrophilic substrates, allowed to form various difluoromethylene containing compounds in a one-pot process. [8±11] Among several reactions already described, the Mukaiyama aldol reaction with ethanal dimethylacetal [8] and allylation with prenyl esters [9] prompted us to apply our methodology to glycoside and glycal derivatives, respectively, in order to have access to the interesting class of difluoro mimics of glycosides (Scheme 3).…”