Alain Krief

Efficicient, high yield, oxidation of thiols and selenols to disulphides and diselenides

Abstract Thiols and selenols are smoothly oxidised in high yield to disulphides and diselenides by sodium perborate at room temperature.

Synthesis of selenoacetals

Abstract This paper reports our results concerning the syntheses of various bis(alkylseleno)alkanes and some of their arylseleno analogues by different methods. The scope and limitation of each of them are presented.

Stereoselective synthesis of methyl (1R) trans- and (1R) cis-hemicaronaldehydes from natural tartaric acid : application to the synthesis of s-bioallethrin and deltamethrin insecticides

Abstract Very efficient enantioselective syntheses of (1R)- trans -and cis -hemicaronaldehydes precursors of (1R)-trans chrysanthemic acid and its (1R)-cis dibromovinyl analogue starting from natural tartaric acid or D-mannitol are described. They are based on the reaction between isopropylidenetriphenylphosphorane or isopropylidenediphenylsulfurane and chiral γ-alkoxy-α,β-unsaturated esters. The general problem of the diastereoselective addition to such esters is discussed.

Synthesis of diselenides and selenides from elemental selenium

Abstract Sodium hydride is able to reduce elemental selenium to sodium diselenide (Na 2 Se 2 ), but not to sodium selenide (Na 2 Se). Dialkyl diselenides and even dialkyl selenides, including unsymmetrical dialkyl selenides, can be nevertheless synthesized using the proper Se/NaH ratio (1/1 or 1/2).

CHEMOSELECTIVE REDUCTION OF ORGANOSELENOCYANATES TO DISELENIDES AND SELENOLATES

Abstract Selenocyanates produce selenolates or diselenides on reaction with metal hydrides (NaH, LiHBEt 3 , LiBH 4 , NaBH 4 ). The former transformation is performed with 2 molar equivalents of sodium hydride or lithium triethyl borohydride or 1.25 molar equivalent of metal borohydrides. The second one is performed with lower amount of reducing agent (1 molar equivalent of sodium hydride or lithium triethyl borohydride or 0.25 equivalent of metal borohydrides). Intermediate formation of a selenol or a selenolate which reacts on the unreacted selenocyanate is suspected in the later transformation.

Self-generated hierarchically porous titania with high surface area: Photocatalytic activity enhancement by macrochannel structure

Various hierarchical porous titania with high surface area over 600 m(2)/g have been synthesized via a spontaneous self-formation process from titanium alkoxides by a water adjusting approach using acetonitrile as reaction medium. The reactivity of metal alkoxides and the water content in acetonitrile medium on the resultant structure have been investigated. The porosities of the products were characterized by SEM, TEM and N(2) adsorption-desorption measurements. The observation on the evolution of porous structure with increasing water content in reaction system is essential for a better understanding of hierarchical porous structure formation over different length scales by this self-formation process. The creation of macro/micropores in photocatalytic titania materials has been found to enhance the photocatalytic activity due to both the action of macrochannels as light harvester and the easy diffusion effect of organic molecules. The present work shows clearly that hierarchically porous titania with the presence of macroporous structure and high surface area can be very efficient photocatalysts, suggesting their potential applications in water treatment as decontamination materials.

From tartaric acid to the most biologically active insecticides: Straightforward enantioselective synthesis of deltamethrin

Abstract Isopropylidenediphenylsulfurane reacts with γ-alkoxy αβ—unsaturated esters and produces γ—alkoxy cyclopropane carboxylates. This reaction is almost completely stereospecific and takes place with very high asymmetric induction. It has been successfully applied for the enantioselective synthesis, from natural tartaric acid, of deltamethrin the most active insecticide commercially available.

Synthesis of α-selenoalkyllithium compounds

Abstract α-Phenylselenoalkyllithiums and α-methylselenoalkyllithiums have been prepared from the corresponding selenoacetals and alkyllithiums. Several features of this reaction are disclosed. For example, the reaction is more readily achieved on phenylselenoacetals than on methylseleno analogues. Those derived from hindered carbonyl compounds are less readily cleaved.s-BuLi/THF proved superior to n-BuLi in THF, itself better than n-BuLi in ether.

Diastereoselective synthesis of dimethyl cyclopropane-1,1-dicarboxylates from a γ-alkoxy-alkylidene malonate and sulfur and phosphorus ylides

Abstract Isopropylidene diphenylsulfurane and isopropylidene triphenylphosphorane react by the same ( Re ) face of the alkylidene malonate derived from the acetonide of ( d )-glyceraldehyde to produce almost exclusively a single diastereoisomer of the corresponding dimethyl cyclopropane-1,1-dicarboxylate.

Synthesis of arylcycloalkanes from ω-alkenyl benzylselenides

Abstract Arylcycloalkanes are produced from ω-alkenyl benzylselenides on reaction with alkyllithiums or on Lewis acid mediated electrophilic cyclisation.