Andrea Temperini

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.

Alkynyl phenyl selenides as convenient precursors for the synthesis of stereodefined trisubstituted alkenes

Abstract The addition of p-toluensulfonic acid to alkynyl phenyl selenides is regio- and stereospecific and affords (Z)-α-(phenylseleno)vinyl p-toluensulfonates in good yield. α-(Phenylseleno)vinyl halides are obtained from the reactions of these compounds with magnesium halides. The reactions of (Z)-α-(phenylseleno)vinyl p-toluensulfonates with cyanocuprates afford the corresponding trisubstituted alkenes in which the tosyl group has been selectively substituted by an aryl or an alkyl group with retention of configuration. Finally, the cross coupling reaction of these vinyl selenides with methylmagnesium bromide, in the presence of a nickel catalyst, occurs with retention of configuration and affords the selenium free trisubstituted alkenes.

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.

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.

IODOSOBENZENE DIACETATE AND DIPHENYL DISELENIDE : AN ELECTROPHILIC SELENENYLATING AGENT OF DOUBLE BONDS

Abstract Phenylseleno-acetoxylation, hydroxylation, etherification and lactonization products are obtained in good yields from the reaction of alkenes with diphenyl diselenide and iodosobenzene diacetate, in acetonitrile. present address: Dipartimento di Scienza degli Alimenti, Universita di Napoli “Federico II” Via Universita, 100 - 80055-Portici, Napoli-Italy. e-mail tingoli@unina.it.

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.