Sinisa Marinkovic

Efficient radical addition of tertiary amines to alkenes using photochemical electron transfer

An efficient photoinduced radical addition of tertiary amine, mainly cyclic derivatives, to electron-deficient alkenes was developed. The reaction was applied to the asymmetric synthesis of the pyrrolizidine alkaloids laburnine and isoretronecanol. The method was then optimized for the addition of a larger variety of tertiary amines, in particular acyclic ones. Radical tandem addition cyclization reactions with unsaturated tertiary amines have also been investigated. A detailed mechanistic study using isotopic labeling enabled the optimization of a corresponding reaction with N,N-dialkylaniline derivatives. The origin of the high reaction stereoselectivity achieved with menthyloxyfuranone was elucidated. The radical addition of tertiary amines was also performed with heterogeneous photocatalysis using inorganic semiconductors as sensitizers.

Direct conversion of xylan into alkyl pentosides

Xylan has been used as a raw material in the synthesis of butyl, octyl and decyl glycosides. Mixtures of D-xylose-, L-arabinose- and D-glucose-based surfactants were obtained under smooth conditions with high yields in a one-pot process. The surface activities of octyl and decyl glycosides thus obtained have been studied and compared with that of pure alkyl D-xylosides. The results have confirmed that the new synthetic approach described in this paper is a potentially economical and efficient method for the preparation of environmentally friendly surfactants.

Thiocarbonyl compounds as regulating reagent in the radical addition of tertiary amines with alkenes using photoelectron transfer conditions

The efficiency of the photoinduced radical addition of tertiary amines to olefinic double bonds is significantly enhanced and the stereoselectivity is influenced when thiocarbonyl compounds are added to the reaction mixture.

NaBr/DMSO-Induced Synthesis of 2,5-Diformylfuran from Fructose or 5-(Hydroxymethyl)furfural

2,5‐Diformylfuran (DFF) was obtained by heating a solution of 5‐(hydroxymethyl)furfural in DMSO. The addition of acids or salts improved the selectivity, especially if bromides were employed. Good yields of DFF were obtained with HBr or NaBr as the catalyst. One‐pot procedures were developed from fructose, which led to DFF in medium yields. This transformation occurs through the formation of 5‐(bromomethyl)furan‐2‐carbaldehyde followed by a Kornblum‐type reaction. In the presence of bromide salts, the in situ formation of the catalyst involves the thermolysis of DMSO and the association of the resulting strong acids with the bromides.

Direct conversion of wheat bran hemicelluloses into n-decyl-pentosides

Direct preparation of pentose based surfactants has been achieved by a direct conversion of wheat bran hemicelluloses in decanol under smooth conditions. Hemicelluloses have been efficiently converted in a single step operation. The wheat-based surfactants thus obtained have shown good surface properties compared to other alkyl glycosides. In view of the growing importance of renewable resource based molecules in detergents and cosmetics industries, this approach may open a new avenue for the production of green surfactants.

Semiconductors as sensitisers for the radical addition of tertiary amines to electron deficient alkenes

Using heterogeneous photocatalysis, the radical addition of tertiary amines with electron deficient alkenes can be performed in high yields (up to 98%) and high facial diastereoselectivity. The photochemical induced electron transfer process initiates the radical chain reaction and inorganic semiconductors like TiO2 and ZnS were used. According to the proposed mechanism, the reaction takes place at the surface of the semiconductor and the termination step results from an interfacial electron transfer from the conduction band to the oxoallyl radical intermediate. Frequently, semiconductors are used for the mineralisation of organic compounds in wastewater. However, in this case, they are used in organic synthesis. The process can be performed in a convenient way and is particularly interesting from the ecological and economical point of view. No previous functionalization of the tertiary amines is necessary for C − C bond formation. Further on, the amines are used both as reactant and as solvent. The excess is recycled by distillation and the inexpensive sensitiser can be easily removed by filtration. In this way, products of high interest for organic synthesis are obtained by a diastereoselective radical reaction.

Acid-Assisted Ball Milling of Cellulose as an Efficient Pretreatment Process for the Production of Butyl Glycosides

Ball milling of cellulose in the presence of a catalytic amount of H2SO4 was found to be a promising pre-treatment process to produce butyl glycosides in high yields. Conversely to the case of water, n-butanol has only a slight effect on the recrystallization of ball-milled cellulose. As a result, thorough depolymerization of cellulose prior the glycosylation step is no longer required, which is a pivotal aspect with respect to energy consumption. This process was successfully transposed to wheat straw from which butyl glycosides and xylosides were produced in good yields. Butyl glycosides and xylosides are important chemicals as they can be used as hydrotropes but also as intermediates in the production of valuable amphiphilic alkyl glycosides.

Photochemical Electron Transfer Mediated Addition of Naphthylamine Derivatives to Electron-Deficient Alkenes

Using photochemical electron transfer, N,N-dimethylnaphthylamine derivatives are added to α,β-unsaturated carboxylates. The addition takes place exclusively in the α-position of electron-deficient alkenes and mainly in the 4-position of N,N-dimethylnaphthalen-1-amine. A minor regioisomer results from the addition in the 5-position of this naphthylamine. A physicochemical study reveals that the fluorescence quenching of N,N-dimethylnaphthalen-1-amine is diffusion-controlled and that the back electron transfer is highly efficient. Therefore no transformation is observed at lower concentrations. To overcome this limitation and to induce an efficient transformation, minor amounts of water or another proton donor as well as an excess of the naphthylamine derivative are necessary. A mechanism involving a contact radical ion pair is discussed. Isotopic labeling experiments reveal that no hydrogen is directly transferred between the substrates. The hydrogen transfer to the furanone moiety observed in the overall reaction therefore results from an exchange with the reaction medium. An electrophilic oxoallyl radical generated from the furanone reacts with the naphthylamine used in excess. Concerning some mechanistic details, the reaction is compared with radical and electrophilic aromatic substitutions. The transformation was carried out with a variety of electron-deficient alkenes. Sterically hindered furanone derivatives are less reactive under standard conditions. In a first experiment, such a compound was transformed using heterogeneous electron transfer photocatalysis with TiO(2).

Efficient radical addition of tertiary amines to electron-deficient alkenes using semiconductors as photochemical sensitisers.

Tertiary amines can be added to electron-deficient alkenes with yields up to 98% in a radical chain reaction initiated by a photochemical electron transfer using inorganic semiconductors like TiO2 as sensitiser.

Low Catalyst Loadings for the Production of Carboxylic Acids from Polysaccharides and Hydrogen Peroxide

The oxidation of starch, xylans, potato flesh and wheat flour by H(2)O(2), in the presence of MSO(4) (M=Cu, Fe) as catalyst, led to depolymerization, and formation of solutions containing polyhydroxycarboxylic acids. Some of these oxidized compounds facilitate the process, leading to efficient transformations even with very low amounts of catalyst.