Secondary alkyllithium reagents bearing an OTBS group (TBS=tert-butyldimethylsilyl) at the 3-position can be prepared stereoconvergently through an I/Li exchange from a diastereomeric mixture of the corresponding secondary alkyl iodides. These lithium reagents react with a range of electrophiles, including carbon electrophiles, with retention of configuration to yield various 1,3-difunctionalized derivatives with good diastereoselectivities. Kinetic studies show that the 3-siloxy group strongly accelerates the epimerization at the lithium-substituted carbon atom. This method offers a new way to construct chiral open-chain molecules with excellent stereoselectivity.