Stereoselective Synthesis of Pyrrolidines via Hydrozirconation-Cyclization

Significance

A diastereoselective synthesis of 2,5-disubstituted pyrrolidines from chiral N-allyl oxazolidines via a tandem hydrozirconation-Lewis acid mediated cyclization is described. Two different pathways are proposed for the BF₃·OEt₂- and TiCl₄-catalyzed process leading to opposite ste­reoselectivity. The TiCl₄-mediated reaction is suggested to occur via an S_N2 mechanism resulting in inversion of configuration at C2, while the BF₃·OEt₂-mediated reaction gave the retention product via attack of the iminium ion intermediate.