Formal [3+2] and [3+3] additions of acceptor-substituted cyclopropyl methylsilanes to allenylsilanes

1,3-Dipolar synthons formed from vicinal TBDPS-substituted cyclopropyl alkyl/phenyl ketones on treatment with Lewis acids such as TiCl4 and Et2AlCl reacted with allenylsilanes to furnish [3 + 2] and [3 + 3] adducts with high regio- and stereocontrol.