Luana Bagnoli

Preparation of a new chiral non-racemic sulfur-containing diselenide and applications in asymmetric synthesis.

The synthesis of the new chiral non-racemic sulfur-containing diselenide, di-2-methoxy-6-[(1S)-1-(methylthio)ethyl]phenyl diselenide, is described. When treated with ammonium persulfate this diselenide is transformed into the corresponding selenenyl sulfate, which acts as a strong electrophilic reagent and adds to alkenes, in the presence of methanol or water, to afford the products of selenomethoxylation or selenohydroxylation, respectively, with excellent diastereoselectivities. Starting from alkenes containing internal nucleophiles, asymmetric cyclofunctionalization reactions also resulted in good chemical yields, complete regioselectivities, and high diastereoselectivities. This sulfur-containing diselenide can also be used in catalytic amounts to promote one-pot selenenylation-deselenenylation processes, from which several types of products can be obtained in high yield and with good enantiomeric excess.

New nitrogen containing chiral diselenides: synthesis and asymmetric addition reactions to olefins

Abstract A simple synthesis of two new nitrogen containing diselenides, 7 and 8 , is described. These compounds were employed as starting materials to effect the asymmetric methoxyselenenylation, the hydroxyselenenylation as well as the cyclofunctionalization of olefins. Starting from 7 all these addition processes occurred with good facial selectivity. Poor results were however obtained with 8 . One-pot selenenylation–elimination sequences using catalytic amounts of the diselenide 7 have also been investigated.

Efficient asymmetric selenomethoxylation and selenohydroxylation of alkenes with a new sulfur containing chiral diselenide

The synthesis of a new chiral non-racemic sulfur containing diselenide is described. The electrophilic selenium reagent, produced from this diselenide by treatment with bromine and silver triflate, has been used to effect the selenomethoxylation and the selenohydroxylation of alkenes. These addition reactions occurred with good chemical yield and with high diastereoselectivities.

Synthesis of enantiopure 1,4-dioxanes, morpholines, and piperazines from the reaction of chiral 1,2-diols, amino alcohols, and diamines with vinyl selenones.

The reactions of readily available vinyl selenones with enantiopure 1,2-diols, N-protected-1,2-aminoalcohols, and diamines gave substituted enantiopure 1,4-dioxanes, morpholines, and piperazines, respectively, in good to excellent yields. The same procedure was extended to the synthesis of thiomorpholine, benzodiazepine, and benzoxazepine. The reactions proceeded in one pot, in the presence of base, through a simple and novel application of the Michael-initiated, ring-closure (MIRC) reactions. The formed heterocycles constitute a framework that is observed in a large number of pharmaceutical compounds.

A sulfur-containing diselenide as an efficient chiral reagent in asymmetric selenocyclization reactions

Abstract Treatment of the di-2-[(1 S )-1-(methylthio)ethyl]phenyl diselenide with bromine and silver triflate afforded the corresponding selenyl triflate which was used in situ as a strongly electrophilic selenium reagent to effect the asymmetric synthesis of oxygen- or nitrogen-containing heterocycles. Cyclic ethers, lactones, lactams or N -protected pyrrolidines have been prepared in good yield with complete regioselectivity and high diastereoselectivity.

ASYMMETRIC SELENOMETHOXYLATION OF ALKENES WITH CAMPHORSELENENYL SULFATE

Abstract By reaction with ammonium persulfate the easily available diselenide derived from (1 R )-(+)-camphor was converted into the camphorselenenyl sulfate. This chiral electrophilic selenium reagent reacted at room temperature with alkenes in the presence of methanol to afford selenomethoxylated adducts in good yields and with moderate to good facial selectivity. The two diastereomeric addition products could be separated in most cases.

Optically active isoxazolidines and 1,3-amino alcohols by asymmetric selenocyclization reactions of O-allyl oximes

Abstract The selenyl triflate generated from the reaction of di-2-[(1 S )-1-(methylthio)ethyl]phenyl diselenide with silver triflate reacts with various substituted O -allyl oximes to promote ring closure, which affords optically active isoxazolidines in high yields and with good diastereoselectivity (up to 93:7). Enantiomerically enriched 1,3-amino alcohols can be easily obtained by N  O bond cleavage of these heterocycles, which was readily effected by treatment with zinc in aqueous acetic acid.

Efficient asymmetric selenocyclizations of alkenyl oximes into cyclic nitrones and 1,2-oxazines promoted by sulfur containing diselenides

Abstract Treatment of the di-2-[(1 S )-1-(methylthio)ethyl]phenyl diselenide or of the di-2-methoxy-6-[(1 S )-1-methylthio)ethyl]phenyl diselenide with bromine and silver triflate afforded the corresponding electrophilic selenylating triflates which were used in situ to promote the asymmetric selenocyclization of γ-alkenyl oximes and δ-phenyl-γ-alkenyl oximes. The course of these reactions and hence the structures of the cyclization products were dictated by the ( E )- or ( Z )-geometry of the starting oximes. The two types of cyclization products were either the cyclic nitrones or the 1,2-oxazines; in both cases the reactions proceeded with excellent yields, complete regioselectivity and good diastereoselectivity.

Asymmetric oxyselenenylation–deselenenylation reactions of alkenes induced by camphor diselenide and ammonium persulfate. A convenient one-pot synthesis of enantiomerically enriched allylic alcohols and ethers

Abstract The reaction of β,γ-unsaturated esters and nitriles with camphor diselenide and ammonium persulfate in methanol, ethylene glycol or water affords enantiomerically enriched γ-alkoxy or γ-hydroxy α,β-unsaturated derivatives, respectively, in good chemical yields and with moderate to good enantioselectivity.

Selenium Catalyzed Oxidation of Aldehydes: Green Synthesis of Carboxylic Acids and Esters

The stoichiometric use of hydrogen peroxide in the presence of a selenium-containing catalyst in water is here reported as a new ecofriendly protocol for the synthesis of variously functionalized carboxylic acids and esters. The method affords the desired products in good to excellent yields under very mild conditions starting directly from commercially available aldehydes. Using benzaldehyde as a prototype the gram scale synthesis of benzoic acid is described, in which the aqueous medium and the catalyst could be recycled at last five times while achieving an 87% overall yield.