Heteroallyl and alpha-Heterosubstituted Allyllithium Reagents

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This grant in Organic and Macromolecular Chemistry provides support for Dr. Lloyd Jackman, Pennsylvania Stata University. The work focuses on the chemistry and mechanisms of various organic salts, particularly those involving lithium. These species are among the most important reagents used in synthetic chemistry and an understanding of their fundamental aspects has important practical significance. The most important single group of synthetically useful organic reactions is that based on ambident anions of the type C=C-X(-). The number of representatives of this group is rapidly increasing. A proper mechanistic understanding of the reactions of these anions with electrophiles does not exist, in part because the structures of the ambident anion salts in solution are usually unknown. With methodologies for solving such structural problems in the case of lithium salts, this study will extend our knowledge by effecting a comparison between the 13C, 6Li, and 7Li nmr spectral characteristics in solution with those in the solid state for known crystal structures. All the above techniques will be applied to lithium enolates, ester enolates and enamides and to heterosubstituted allyllithium reagents. It is becoming clear that mixed aggregates (dimers, tetramers) between lithium carbanion salts and lithium salts which are strong electrolytes are important entities in weakly polar solvents in that they control rates and regiochemistry. The thermodynamics of mixed aggregate formation will be studied in order to determine the factors controlling their stabilities. The structural information will be used in conjunction with reaction kinetics to establish the reaction mechanisms of the transesterification of lithium phenolates, the aldol reaction, and the alkylation of phenolates, enolates, and enamides. Particular emphasis will be placed on defining the primary reactant species and understanding the role of mixed aggregates as intermediate species. The involvement of coordination induced proximity effects arising when the electrophilic reagents possess basic centers which can interact with lithium in aggregates will also be probed. The reactions to be studied include some that are widely used in synthetic organic chemistry. The results of these studies should allow synthetic chemists to perform them more efficiently and to design new ones for achieving high regio- and stereo-selectivities.