A novel approach to 2-substituted-2-(dimethoxyphosphoryl)-pyrrolidines 7a-7o and 9a-9r has been developed, which features a TMSOTf-mediated one-pot intramolecular cyclization and phosphonylation of substituted tert-butyl 4-oxobutylcarbamates. The major advantages of this method include simple operation under mild reaction conditions, the use of cheap Lewis acid, and good to excellent yields with high diastereoselectivities (dr up to 99:1).