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  • Lithium diisopropylamide-mediated ortholithiation and anionic fries rearrangement of aryl carbamates: role of aggregates and mixed aggregates.

Lithium diisopropylamide-mediated ortholithiation and anionic fries rearrangement of aryl carbamates: role of aggregates and mixed aggregates.

Journal of the American Chemical Society (2006-10-19)
Kanwal Jit Singh, David B Collum
ABSTRACT

Structural and mechanistic studies of the lithium diisopropylamide (LDA)-mediated anionic Fries rearrangements of aryl carbamates are described. Substituents at the meta position of the arene (H, OMe, F) and the dialkylamino moiety of the carbamate (Me(2)N, Et(2)N, and i-Pr(2)N) markedly influence the relative rates of ortholithiation and subsequent Fries rearrangement. Structural studies using (6)Li and (15)N NMR spectroscopies on samples derived from [(6)Li,(15)N]LDA reveal an LDA dimer, LDA dimer-arene complexes, an aryllithium monomer, LDA-aryllithium mixed dimers, an LDA-lithium phenolate mixed dimer, and homoaggregated lithium phenolates. The highly insoluble phenolate was characterized as a dimer by X-ray crystallography. Rate studies show monomer- and dimer-based ortholithiations as well as monomer- and mixed dimer-based Fries rearrangements. Density functional theory computational studies probe experimentally elusive structural and mechanistic details.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Diisopropylamine, puriss. p.a., ≥99.0% (GC)
Supelco
Diisopropylamine, analytical standard
Sigma-Aldrich
Diisopropylamine, purified by redistillation, 99.95%
Sigma-Aldrich
Lithium diisopropylamide solution, 2.0 M in THF/heptane/ethylbenzene
Sigma-Aldrich
Diisopropylamine, ≥99.5%