Abstract: This invention encompasses a process for preparing higher order cuprate complexes which contain a carbanion for the formation of carbon to carbon bonds in reactions such as epoxide addition. The complex is formed by reacting a first cuprate complex with a stannane such that the carbanion to be used to form carbon to carbon bonds is transferred from the stannane to the first cuprate complex to form a different higher order cuprate complex. This process permits the in situ preparation of a higher order cuprate complex having the carbanion desired to be used in a synthetic reaction. Higher order cuprate complexes derived from the reaction of a cuprate complex with 1,2-bis-tri-n-butylstannyl ethylene are particularly useful for the addition to epoxides to form vinyl tin intermediates useful for preparing omega side chains of prostaglandins.