Microsolvation and sp²-stereoinversion of monomeric α-(2,6-di-tert-butylphenyl)vinyllithium as measured by NMR

• Rudolf Knorr,
• Monika Knittl and
• Eva C. Rossmann

Beilstein J. Org. Chem. 2014, 10, 2521–2530, doi:10.3762/bjoc.10.263

• pair intermediate; monomeric alkenyllithiums; pseudoactivation parameters; sp2-stereoinversion mechanism; THF catalysis; Introduction Organolithium compounds tend to aggregate in solution unless the structure of their carbanionic part favors the nonaggregated (monomeric) species [2]. For example

• the required migration shown in 13 during stereoinversion of the carbanion, as had been postulated [11] for 1. This proposal is now supported in Table 2 through the similar pseudoactivation parameters of 4&3THF (entry 3, Table 2), 2&3THF (entry 2, Table 2), and 1a&3THF (entry 1, Table 2). Although

• ‡. For a critical evaluation of these pseudoactivation parameters, it may be recalled [10][11] that the “true” activation enthalpies ΔH‡ will be almost equal to ΔHψ‡, whereas true ΔS‡ will be more negative than ΔSψ‡ by a mathematical correction of roughly R ln[free THF] = up to 5 cal mol−1 K−1