Breaking the tert-Butyllithium Contact Ion Pair: A Gateway to Alternate Selectivity in Lithiation Reactions.
J Am Chem Soc
; 145(19): 10743-10755, 2023 May 17.
Article
em En
| MEDLINE
| ID: mdl-37133911
ABSTRACT
The effects of Lewis basic phosphoramides on the aggregate structure of t-BuLi have been investigated in detail by NMR and DFT methods. It was determined that hexamethylphosphoramide (HMPA) can shift the equilibrium of t-BuLi to include the triple ion pair (t-Bu-Li-t-Bu)-/HMPA4Li+ which serves as a reservoir for the highly reactive separated ion pair t-Bu-/HMPA4Li+. Because the Li-atom's valences are saturated in this ion pair, the Lewis acidity is significantly decreased; in turn, the basicity is maximized which allowed for the typical directing effects within oxygen heterocycles to be overridden and for remote sp3 C-H bonds to be deprotonated. Furthermore, these newly accessed lithium aggregation states were leveraged to develop a simple γ-lithiation and capture protocol of chromane heterocycles with a variety of alkyl halide electrophiles in good yields.
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MEDLINE
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En
Ano de publicação:
2023
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Article