New stable reagents for the nucleophilic trifluoromethylation. Part 2: Trifluoromethylation with silylated hemiaminals of trifluoroacetaldehyde

Trifluoromethylation of Nonenolizable Carbonyl Compounds with a Stable Piperazino Hemiaminal of Trifluoroacetaldehyde

“…[8] This new stable compound is able to trifluoromethylate nonenolizable carbonyl compounds by fluoride activation. However, as shown in Scheme 1, its synthesis needs the intermediate preparation of the free hemiaminal 1, which can easily be purified by precipitation from its dichloromethane solution with pentane.…”

“…Furthermore, the nature of the base counter-cation plays a crucial role. Indeed, if we assume, according to our previous work, [8] that the trifluoromethylating species is the hemiaminolate 3 (Scheme 2), the better the ion pair is separated, the better the generation of CF 3 Ϫ : reagents 3 forming tight ionic pairs [Li salts (entries 4 and 8) or Na salts (entries 3 and 6)] or too covalent OϪM bonds [Mg salts (entry 9)] do not lead to the expected product 2a. Negative results were also obtained with amines (entries 10Ϫ12), which are probably not basic enough to deprotonate 1.…”

From fluoral to heterocycles: a survey of polyfluorinated iminiums chemistry

“…The first stable hemiaminal we succeeded to synthesize in a good yield, starting from methyl hemiketal of fluoral (a commercially available form of fluoral), was the N-benzylpiperazine derivative [9]. Since hydrates of other fluorinated aldehydes are commercially available, related hemiaminals have been similarly synthesized, from chlorodifluoroacetaldehyde and pentafluoropropionaldehyde hydrates [10] (Scheme 2).…”

“…In this respect, we have recently described a new class of versatile and broad-scope reagents, arising from fluoral, namely the hemiaminals of fluoral [9][10][11][12]. These easily synthesized hemiaminals are able, depending on the conditions, to generate different fluorinated reactive intermediates for the preparation of various fluorinated products (Scheme 1).…”

Novel and efficient approach to (Z)-4-trifluoroethylidene-1,3-dioxolane derivatives via (trifluoromethyl)ethynylation of ketones and aldehydes

“…Herein, we wish to report a novel and efficient method for the synthesis of 4-trifluoroethylidene-1,3-dioxolane derivatives via new stable (trifluoromethyl)ethynylation reagent [8][9][10][11][12] and mechanistic rationalization for the formation of these compounds.…”