研究目的
Investigating the enantioselective formation of 3-cyclopropylquinolones via triplet-sensitized deracemization using visible light and a chiral sensitizer.
研究成果
The study demonstrates that cyclopropanes undergo triplet-sensitized deracemization using a chiral thioxanthone sensitizer under visible light, leading to enantioselective formation of 3-cyclopropylquinolones with yields of 88-96% and enantioselectivities up to 55% ee. The enantiodifferentiation occurs through a deracemization process rather than initial product formation, with different association constants and sensitization rates for enantiomers. This photochemical approach is unique and offers potential for further improvements in enantioselectivity.
研究不足
The enantioselectivities achieved are moderate (up to 55% ee) and could be improved. The mechanism involves complex equilibria and sensitization rates, which may limit control over selectivity. The reaction is specific to certain substrates and conditions, and further optimization is needed for broader applicability.
1：Experimental Design and Method Selection:
The study involved photochemical reactions using visible light irradiation (λ = 420 nm) with a chiral thioxanthone sensitizer to promote enantioselective di-π-methane rearrangement of 3-allyl-substituted quinolones. A merry-go-round reactor with fluorescent lamps or LEDs was used for irradiation.
2：Sample Selection and Data Sources:
Substrates were 3-allyl-substituted quinolones (e.g., 5a, 5c-5j) synthesized as described in the Supporting Information.
3：List of Experimental Equipment and Materials:
Merry-go-round reactor, fluorescent lamps (8 W each, emission at 420 nm), LED (420 nm, 2 W), solvents (trifluorotoluene, hexafluoro-meta-xylene, acetonitrile), chiral sensitizer (thioxanthone 4), achiral sensitizer (9-thioxanthenone 7), HPLC for analysis, X-ray diffraction for absolute configuration determination.
4：Experimental Procedures and Operational Workflow:
Reactions were performed at concentrations of
5：5 mM in specified solvents and temperatures. Irradiation times varied (5-5 h). Products were isolated and analyzed by HPLC for enantiomeric excess. Racemization studies and association constants were measured using NMR titration. Data Analysis Methods:
Enantiomeric excess was determined by HPLC with chiral stationary phase. Triplet energies were measured. Association constants were calculated from NMR data. DFT calculations (M06-2X functional, Grimme D3 dispersion, def2-TZVP basis set) were used for mechanistic insights.
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