TETRAHEDRON: ASYMMETRY Tetrahedron: Asymmetry 12 (2001) 1493–1502 Pergamon A sulfur-containing diselenide as an efficient chiral reagent in asymmetric selenocyclization reactions Marcello Tiecco,* Lorenzo Testaferri, Francesca Marini, Silvia Sternativo, Luana Bagnoli, Claudio Santi and Andrea Temperini Dipartimento di Chimica e Tecnologia del Farmaco, Sezione di Chimica Organica, Universita ` di Perugia, I -06123 Perugia, Italy Received 12 May 2001; accepted 29 May 2001 Abstract—Treatment of the di-2-[(1S )-1-(methylthio)ethyl]phenyl diselenide with bromine and silver triflate afforded the corre- sponding 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. © 2001 Elsevier Science Ltd. All rights reserved. 1. Introduction In recent years the introduction of a large number of chiral non-racemic diselenides 1–3 has greatly renewed interest in organoselenium chemistry. Optically active diselenides could in fact be easily converted into elec- trophilic reagents which were successfully employed to effect efficient asymmetric addition reactions to alkenes. On the basis of much experimental evidence it has been proposed 3–5 that the high stereoselectivity observed with these reagents is due to a non-bonded interaction, which occurs between the selenium atom and an oxygen or nitrogen atom positioned in close proximity. Such an interaction forces the stereogenic center to approach the reaction center during the addition, thus improving the chirality transfer. In an attempt to make this inter- action more efficient and hence to increase the diastereoselectivity of the asymmetric addition reac- tions, we have recently introduced the new diselenide 1 6 where sulfur takes the place of the oxygen or nitrogen atom (Scheme 1). Treatment of 1 with bromine and silver triflate afforded the corresponding selenyl triflate 2, which was employed to effect very efficient asymmet- ric selenomethoxylations and selenohydroxylations of alkenes. 6 The addition of 2 to an alkene gives rise to a mixture of two diastereomeric seleniranium intermedi- ates 3 which are trapped by the nucleophile to afford a mixture of the two enantiomerically pure diastereo- meric addition products 4. The reaction is a stereo- specific anti addition and the alkoxy- and hydroxy- Scheme 1. * Corresponding author: Tel.: +39 075 5855100; fax: +39 075 5855116; e-mail: tiecco@unipg.it 0957-4166/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII:S0957-4166(01)00248-8