RESUMEN
CF2H-Pseudoprolines obtained from difluoroacetaldehyde hemiacetal and serine are stable proline surrogates. The consequence of the incorporation of the CF2H group is an important decrease of the trans to cis amide bond isomerization energy and a remarkable stabilisation of the cis conformer by an hydrogen bond.
Asunto(s)
Péptidos/química , Prolina/análogos & derivados , Tiazoles/química , Tolueno/análogos & derivados , Enlace de Hidrógeno , Metilación , Conformación Molecular , Prolina/química , Estereoisomerismo , Tolueno/químicaRESUMEN
The preparation of 3,3-difluoro-6-methylhept-5-en-2-one 1, a key intermediate for the synthesis of 4,4-difluoroterpenes, and applications in linalool and geraniol series are described. The process involves 1,1-difluoro-2-trimethylsilyoxypropene, an enol silyl ether prepared from acetyltrimethylsilane and trifluoromethyltrimethylsilane, and its reaction in situ with prenyl benzoate, under catalysis by trimethylsilyl trifluoromethanesulfonate. Optimized conditions leading to either the desired enol silyl ether or the unprecedented methyl(trifluoromethyl)trimethylsilyl carbinol 4 have been achieved. The prenylation of the enol silyl ether gives a 9/1 mixture of regioisomers, in favor of the expected ketone 1. Treatment of 1 with vinylmagnesium bromide leads to (+/-)-4,4-difluorolinalool 7. Reaction with the lithium enolate of ethyl diethylphosphonoacetate, and then LAH reduction, converts 1 to 4,4-difluorogeraniol 11, with complete stereoselectivity.
RESUMEN
Difluoroenoxysilanes, prepared from acylsilanes and trifluoromethyltrimethylsilane under fluoride activation, were glycosylated with some glycosyl donors (acylglycosides, glycals) to yield difluoro-C-glycosides with a difluoromethylene group in the place of the anomeric oxygen. This reaction strongly depends on the substituent in the 2-position of the glycosyl donor. Application of this methodology to a xylose-derived acylsilane led to the formation of difluoro-C-disaccharides as an isosteric O-glycosyl mimetic.
RESUMEN
Difluoroaldol compounds 3 were synthesized in a one-pot procedure involving an acylsilane 1, trifluoromethyltrimethylsilane (TFMTMS), and an aldehyde. The key intermediate of this reaction is a difluoroenoxysilane 2. Ytterbium triflate proved to be a very efficient catalyst for promoting the aldol type reaction under very mild conditions. The potential of this reaction for the convergent synthesis of difluorinated compounds was illustrated by the synthesis of difluoroegomaketone 7d through dehydration of the corresponding aldol compound 3d.
RESUMEN
The synthesis and surface behavior of a series of nine new hydrogenated nonionic surfactants and their fluorinated analogs, derived from D-mannitol are described. Adsorption monolayers (Gibbs monolayers) were studied by surface pressure (H) measurements as a function of time. For the spread monolayers (Langmuir monolayers), the measurements of surface pressure versus molecular area (A) were performed. For the most hydrophobic amphiphiles at low concentrations, the adsorption at the air/water interface from the bulk solution required extremely long times to attain equilibrium. The A values for two compounds which could be studied in both adsorbed and spread monolayers provided data allowing a direct comparison of the properties of the two types of films formed at the air/water interface. In spite of different mechanisms of formation of Langmuir and Gibbs monolayers, their characteristic parameters were identical, proving the equivalence of these two types of structures.