PHENYL VINYL SELENONE AS A USEFUL REAGENT FOR THE STEREOSELECTIVE FORMATION OF CYCLIC BETA-AMINOESTERS

Because of their ready availability, great structural and electronic diversity, easy handling and peculiar chemical behaviour organoselenium compounds are nowadays considered versatile reagents for many synthetic transformations. a,b-Unsaturated selenones represent an interesting example: the electron-withdrawing effect combined with the excellent nucleofugal ability of the phenylselenonyl group makes these compounds useful 1,2-bis(electrophilic) synthons. Recently we have conveniently employed readily available a,b-unsaturated selenones and 1,3-dicarbonyl compounds or cyanoacetates for the organocatalytic asymmetric assembly of structurally complex spirolactones or cyclopropanes. We now report some preliminary results concerning the use of phenyl vinyl selenone and cyclic b-ketoesters for the stereoselective formation of sterically constrained b-aminoesters containing two adjacent stereocenters. The sequential synthesis involves the following steps: a) a highly enantioselective Michael addition catalyzed by a cinchona alkaloid derived catalyst, b) the conversion of the resulting Michael adduct to the corresponding azide by nucleophilic substitution of the phenylselenonyl group, c) a cyclization reaction via a Staudinger/aza-Wittig sequence, d) a diastereoselective reduction of the resulting cyclic imine. b-Aminoesters are obtained with good yields and excellent stereocontrol.