Journal
CHEMICAL SCIENCE
Volume 4, Issue 5, Pages 1995-2005Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c3sc00098b
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Funding
- University of Geneva
- Swiss National Science Foundation [200020_134682/1]
- Swiss National Science Foundation (SNF) [200020_134682] Funding Source: Swiss National Science Foundation (SNF)
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Advances in the efficient palladium-NHC catalysed synthesis of highly enantioenriched 2,3-trans-fused and 2-alkyl indolines via asymmetric C(sp(3))-H activation of an unactivated methylene/methyl group are reported. Very high asymmetric inductions (up to 99% ee) were achieved at reaction temperatures ranging from 120 to 160 degrees C. Factors influencing the efficiency of the reaction (halide, pseudohalide, N-protecting group) were investigated. The reaction pathway and enantioselection were probed by detailed density functional theory (DFT) calculations (M06-L functional). The combined theoretical and experimental study shows that the Pd-NHC catalysed C(sp(3))-H arylation proceeds via a concerted metalation-deprotonation (CMD) mechanism. The CMD step is shown by DFT calculations and kinetic isotope effect measurements to be selectivity-determining. A good agreement between experimental enantioselectivities and calculated differences amongst diastereomeric activation barriers is observed.
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