Charles Portella

Development of Agriculture Left-Overs: Fine Organic Chemicals from Wheat Hemicellulose-Derived Pentoses

This review is dedicated to wheat hemicelluloses and its main components D-xylose and L-arabinose as raw materials for fine organic chemistry. The context of the wheat agro-industry, its by-products, and extraction and hydrolysis of hemicelluloses to produce the pentoses are considered. The straightforward preparation of pentose-based surfactants, their properties, and their situation in the field of carbohydrate-based surfactants are addressed. Multistep transformations of pentoses are also described, first from a methodology point of view, with the aim of producing multifunctional enantiopure building-blocks, then considering targeted natural and/or bioactive products. Selected reactions of furfural, an important dehydration product of pentoses, are also presented.

C-Difluoromethylene-containing, C-trifluoromethyl and C-perfluoroalkyl carbohydrates. Synthesis by carbohydrate transformation or building block methods

The synthetic methods for preparing carbohydrates bearing a C-branched substituent of the type CF2-Y, with Y = F, Y = CnF(2n + 1) or Y = a carbon-attached or heteroatom-attached nonfluorinated residues, are reviewed. Both direct introduction of C-branched fluorinated substituents (direct trifluoromethylation, perfluoroalkylation or difluoromethylenation) and building block methods from fluorinated synthons are considered.

Mixed organofluorine-organosilicon chemistry. 8. One-pot synthesis of 2,2-difluoro-1,5 diketones from acylsilanes, trifluoromethyltrimethylsilane and enones, and their annulation reaction

Abstract We describe the synthesis of 2,2-difluoro-1,5-diketones in a one-pot procedure from an acylsilane and trifluoromethyltrimethylsilane, via reaction of difluoroenoxysilanes and enones under electrophilic activation. These diketones are interesting building blocks for the synthesis of gem -difluoro enones or substituted fluorophenols, depending on the annulation conditions. The annulation proceeds with complete regioselectivity controlled by the fluorine substitution.

Enzymatic synthesis of alkyl arabinofuranosides using a thermostable α-l-arabinofuranosidase

Abstract A thermostable α- l -arabinofuranosidase was tested for its ability to perform transglycosylation with different alcohol acceptors. Reactions were characterized by high rates with optimal synthesis being obtained within 10 min. Both primary and secondary alcohols could act as acceptors in transarabinosylation but yields of alkyl arabinosides decreased with increasing alkyl chain length.

Photoreductive cyclization of δ,ϵ-unsaturated ketones

Abstract δ,ϵ-unsaturated ketones are efficiently photoreduced in HMPA or tertiary amines. Cyclization to cyclopentanols is the only observed reaction.

Reactions of difluoroenoxysilanes with glycosyl donors: synthesis of difluoro-C-glycosides and difluoro-C-disaccharides.

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.

STEREOSELECTIVITY OF THE NUCLEOPHILIC F-ALKYLATION OF CARBONYLATED CARBOHYDRATES

Abstract The addition of F-alkyl organometallics to carbonylated carbohydrates 1 – 3 was carried out using trimethylsilyl or bromomagnesium reagents. The results are strongly dependent upon both the nature of the metal and of the substrate. Compounds 1 and 2 were transformed with high stereoselectivity into the l -ido adduct using F-organomagnesium reagents, whereas the d -allo adduct was obtained with complete stereoselectivity using fluoride activated addition of F-organosilanes on compound 3 . Comparison with literature data emphasizes the enhanced stereoselectivity exhibited by perfluoroorganometallic reagents. The difference between the stereoselectivity of the addition of magnesium versus silyl reagents was attributed to chelation effects.

Mixed organofluorine - organosilicon chemistry. 6. Synthesis of gem-difluoro-C-glycosides and C-disaccharides from acylsilanes and trifluoromethyltrimethylsilane. An exploratory study

Abstract Difluoroenoxysilanes, prepared from acylsilanes and trifluoromethyltrimethylsilane under fluoride activation, were glycosylated by glucal to yield C -difluoroglycosides with a difluoromethylene group in place of the anomeric oxygen. Application of this methodology to a xylose-derived acylsilane led to a C -difluorodisaccharide.

Fluorinated ketene dithioacetals. Part IX. Synthesis and some chemical properties of new fluorinated 3H-1,2-dithiole-3-thiones

Abstract 4-Fluoro-5-perfluoroalkyl-3 H -1,2-dithiole-3-thiones were prepared by heating the corresponding ketene dithioacetals with magnesium bromide and elemental sulfur. They reacted as dienophiles and 1,3-dipoles in cycloaddition reactions to give new fluorinated organosulfur compounds.

Photoreduction des esters car☐yliques dans l'hexamethylphosphortriamide (HMPT)

Abstract Use of HMPT as solvent in photochemistry allows efficient photoreductions. Alkyl esters and especially non absorbing alkyl acetates are photoreduced in excellent yields into alkanes. In the latter case, a protonating agent is necessary. Numerous examples illustrate the generality and convenience of the reaction. This photoreduction involves an electron transfer from HMPT to ester.