A New Asymmetric Approach Toward 5-Substituted Pyrrolidin-2-one Derivatives

The condensation between a chiral 2-silyloxypyrrole and either achiral or chiral formyl cation equivalents has been studied. The methodology has allowed to build-up 5-substituted pyrrolidin-2-one derivatives with a stereocontrol from good to excellent. The chiral auxiliary located on the silyloxypyrrole showed an intrinsic good level of diastereoface discrimination at C-5. However, the use of a 2-methoxy-3-tosyl-oxazolidine as chiral formylating agent allowed a total stereocontrol in the condensation. A rationale for the observed stereochemical outcome is presented. The stereoselective manipulation of these adducts provided new potentially interesting pyroglutamic aldehyde and prolinal derivatives, whereas treatment with TiCI4 triggered unexpectedly a Pomeranz-Fritsch type intramolecular condensation affording a benzocondensated indolizidinone.