Generation and Use of an Equivalent of Difluoroacetamide or Difluoroacetate Anions Part 3 of the Series: Reactivity of Stable Trifluoroacetaldehyde hemiaminals. Part 2: T. Billard, B. R Langlois, J. Org. Chem. 2002, 67, 997–1000.

Abstract

At the present time, more complex analyses of apolar compounds with similar chemical structures or of polar compounds, especially basic ones, having diverse properties require more selective stationary phases having better stabilities. This paper describes several new stationary phases with directed selectivities that were prepared by immobilizing two different phenyl group‐containing siloxanes and a trifluoropropyl‐containing siloxane onto chromatographic silica and, in the case of the fluorinated siloxane, onto zirconized silica, using thermal treatment or microware radiation. The chromatographic properties and stabilities of these new phases were determined and several applications were evaluated. The phenyl‐containing phases showed excellent characteristics related to the separation of several different types of aromatic compounds while the fluorinated phases, which present a more polar character, revealed selectivity for the separation of positional isomers as well as for a mixture of basic pharmaceuticals. Stability tests indicate that immobilization of the polysiloxanes increases column lifetimes by making the stationary phases less susceptible to dissolution, while the phases immobilized with microwave radiation were somewhat more stable than those immobilized by thermal treatments.

Fluorinated enol ethers: their synthesis and reactivity

“…Difluoroketene hemiaminal 80 derived from a trifluoroacetamide was also added, under TfOSiMe 3 , catalysis to a small range of aromatic and aliphatic aldehydes (Scheme 72). 40 Monofluorinated enol ethers were also used as nucleophiles in Mukaiyama aldol reactions. Welch reported the addition of silyl enol ether 3 derived from 3,3-dimethyl-1-fluorobutan-2-one to benzaldehyde and various aliphatic aldehydes.…”

“…105 The use of acyl chlorides was also reported, first by Iseki using difluoroketene ethyl trimethylsilyl acetal 77 and then by Langlois using his piperazine-derived difluoroketene hemi-aminal 80. 40,106 The addition to acetals was more widely investigated. Portella first reported the SnCl 4 -promoted addition of difluoroenoxysilane 13d to various glycosyl donors.…”

Synthesis of Complex Organofluorine Compounds

“…Higher homologues of perfluoroalkyl lithium compounds are usually generated at very low temperatures (À78 hC or below) in situ and directly reacted with a suitable electrophile, often a carbonyl compound, for example an aldehyde, ketone [45], or ester [46] (Scheme 2.117). If this carbonyl compound is chiral, reasonable diastereomeric excesses can be obtained [47].…”

“…Although the reaction of O-trimethylsilyl difluoroesterenolates with carbonyl compounds leads to the same reaction products as the analogous Reformatsky reaction [41] (Scheme 2.203), use of chiral catalysts results in additions with much greater enantioselectivity [42] (Scheme 2.204). 166 A type of building block with similar reactivity is obtained by elimination of HF from aminals [43] or hemiaminals [44] of trifluoroacetaldehyde [45] [43] and hemiaminals (below) [45].…”

From fluoral to heterocycles: a survey of polyfluorinated iminiums chemistry

“…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).…”