Rearrangements of and within Alkyllithium Aggregates

Although the aggregation of alkyllithium compounds in etheral and other solvents has been known for quite a few years 1J5l I i-i44)i detailed information about the kinds of aggregates and the rearrangements within a certain aggregate or between different aggregates became available only in recent years 145-U7). Because of their importance in mechanistic and synthetic carbanion chemistry 143 148), it therefore seems appropriate to include some of the pertinent results in this review article. 

A systematic study of the structures of thirteen lithiated hydrocarbons and of eighteen a-halolithium carbenoids in donor solvent (R20, R3N) mixtures down to — 150 °C has been performed by Seebach and coworkers 149,150,151). At room temperature no 13C—6Li coupling was observed in the 13C nmr spectrum because of fast inter- and intra-aggregate exchange processes. At lower temperatures ( —70 °Cj these reactions freeze out thus allowing a correlation of the multiplicities of the signals with the 

C—Li coupling constants increase with increasing s-character of the C—Li bond (alkyl- cyclopropyl- vinyl-Li, phenyl-Li). 

Some selected organolithium compounds are discussed in more detail below. 

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