A diastereoselective switch in the access to isobenzofuran-derived alpha-selenoesters

The cycloaddition of 1-phenylisobenzofuran (PIBF) with methyl acrylate yields, in a moderate endo/exo ratio, the expected oxa-bridged adduct, which can be deprotonated and condensed on diphenyl diselenide to provide, in a stereoconvergent step, the "endo" alpha-selenoester. Its "exo" epimer is obtained by reacting PIBF and methyl alpha-phenylselenoacrylate. These adducts can be oxidized to give a common unsaturated bridged ester that can react with an imminium ylide to provide the expected pyrrolidine stereoselectively.