Organo-di-Lithio Reagents: Cooperative Effect and Synthetic Applications

Abstract

The development of organometallic reagents remains one of the most important frontiers in synthetic chemistry. In this review, we summarize our research on the structures, reactions, and synthetic applications of 1,4-dilithio-1,3-butadienes as organo-di-lithio reagents. The 1,4-dilithio-1,3-butadienes bearing a wide variety of substitution patterns on the butadienyl skeleton can be readily prepared in high efficiency. The configuration has been predicted and demonstrated to favor a double dilithium bridging structure in both solution and solid states. The two Li atoms are bridged by a butadiene moiety and are in close proximity. By taking advantage of this unique configuration, we have developed useful and interesting synthetic methodologies. Three types of reactions of 1,4-dilithio-1,3-butadienes have been developed and are discussed: intramolecular reaction, intermolecular reaction, and transmetallation. First, intramolecular reaction is introduced as a result of the intra-cooperative effect among the two C–Li moieties, the butadienyl bridge, and the substituents. A useful transformation from silylated 1,4-dilithio-1,3-butadienes to α-lithio siloles is described. Second, we discuss an intermolecular reaction that results from the inter-cooperative effect of the two C–Li moieties toward substrates. The intermolecular reactions are featured with formation of oxy-cyclopentadienyl dilithium via the reaction of di-lithio reagents with CO and formation of a series of N-heterocycles via the reaction of di-lithio reagents with nitriles. Third, we discuss transmetallation of di-lithio reagents with aluminum, copper, iron, zinc, or barium salts to generate diversified organo-di-metallic or metallacyclic compounds. The dimetallic 1,4-dilithio-1,3-butadienes and their transmetallated derivatives provide unique synthetic organometallic reagents that are different from monometallic reagents, both in terms of reactivity and in synthetic application. These organo-di-metallic reagents provide the access to interesting and useful compounds that are not available by other means, such as N-, O-, and Si-containing heterocycles, strained ring systems, metal-containing macrocycles, and metal complexes bearing new types of ligand.