Lubomír Lochmann

Reaction of Organolithium Compounds with Alkali Metal Alkoxides – A Route to Superbases

Organolithium compounds and lithium alkoxides form adducts, the reactivities of which are similar to those of the parent organolithium compounds. On the other hand, with heavy alkali metal alkoxides a metal interchange takes place, which gives rise to heavy alkali metal organic compounds. This is accompanied by a dramatic increase in the reactivity of the system, hence the name “Superbase” (SB) may be applied. This metal interchange is a general reaction and proceeds not only with organolithium compounds but also with lithium amides and lithium enolates of ketones and esters. SBs readily react with organic substrates to give heavy alkali metal derivatives of the substrate. Such reactions, followed by conversion with an electrophile, find wide application in organic synthesis. The properties of SBs may be further enhanced by using a greater than equimolar amount of a highly-branched heavy alkali metal alkoxide (R2OM). In this review, the mechanism of SB reactions with substrates is discussed and the stoichiometric participation rather than catalytic effect of R2OM is documented. Although various routes for the reaction of SBs with substrates may be envisaged, a heavy alkali metal organic compound is involved in all cases.

50 years of superbases made from organolithium compounds and heavier alkali metal alkoxides

AbstractA review of reactions of organolithium compounds (RLi) with alkali metal alkoxides is presented. On the one hand, simple lithium alkoxides form adducts with RLi the reactivity of which differs only slightly from that of RLi. On the other hand, after mixing heavier alkali metal alkoxides (R’OM, M = Na, K, Rb, Cs) with RLi, a new system is formed, which has reactivity that dramatically exceeds that of the parent RLi. A metal interchange, according to the equation RLi + R’OM = RM + R’OLi, occurs in this system, giving rise to a superbase. This reaction is frequently used for the preparation of heavier alkali metal organometallic compounds. Similar metal interchange takes place between R’OM and compounds such as lithium amides and lithium enolates of ketones or esters, thus demonstrating the general nature of this procedure. Superbases react easily with many types of organic compounds (substrates), resulting in the formation of a heavier alkali metal derivative of the substrate (metalation). The metalated substrate can react in situ with an electrophile to yield the substituted substrate, a procedure that is frequently used in synthetic and polymer chemistry. An improved mechanism of metal interchange and reaction of superbases with substrates is proposed.

Anionic polymerization of acrylates

SummaryThe article presents preliminary results of the anionic polymerization of 2-ethylhexyl- and butyl acrylates initiated by ester enolate in the presence of Li 3-methylpentoxide-3. Compared with the Li t-butoxide which has been widely used earlier, this alkoxide is a more efficient stabilizer of active centers. Under selectively chosen reaction conditions, polymerizations of both monomers proceed quantitatively with a small extent of the selftermination event at-40 and-20°C producing polymers with narrow MWDs.

Micellization of a Novel Type of Hydrophilic/Hydrophobic Block Copolymers

Abstract Hydrophilic/hydrophobic block copolymers, which consist of hydrophilic blocks containing carboxylated polystyrene or poly(4-methylstyrene) chains, resist micellization by routine procedures. Micellization may be achieved in the presence of tris (2-hydroxyethyl)amine (THEA). Apparently, in a THF/water mixture. THEA with carboxyls forms tight ionic pairs that are quite hydrophilic and keep the micelles in solution. The resulting micelles could be transferred into water, aqueous LiCl, and THEA buffer solutions. They were characterized by static and dynamic light scattering and their properties were shown to conform to a typical behavior expected for micellar solutions.