fig2
![Enantioselective synthesis of 6-(Indole-2-yl)-3,4-dihydropyran-2-one skeletons by <i>N</i>-Heterocyclic carbene-catalyzed asymmetric [3 + 3] cycloaddition of α-bromocinnamaldehyde](https://image.oaes.cc/40042901-1e86-452e-bbf6-921d534862d0/CS-2023-14.fig.2.jpg)
Figure 2. Optimization of the reaction conditionsa. aReaction conditions: pre-catalyst (20 mol%), base (1.5 equiv), 1a (0.1 mmol), and 2a (0.12 mmol) in solvent (1.5 mL). bIsolated yield. cDetermined by chiral HPLC analysis. d5Å molecular sieves (10 mg) were used as an additive at room temperature. epre-catalyst (10 mol%). fThe temperature was 0 °C. gThe temperature was 35 °C. hTHF = 3 mL. iTHF = 1 mL. Mes = 2,4,6-trimethylphenyl.
