fig1

Figure 1. Optimization of the reaction condition^a. ^aUnless otherwise noted, 2a (0.4 mmol, 2.0 equiv.) and CDI (0.4 mmol, 2.0 equiv.) in DCE (1 mL) were typically stirred for 2 h. Then, the above solution was added to the mixture of 1a (0.4 mmol, 2.0 equiv.), 3a (0.2 mmol, 1.0 equiv.), NHC catalyst (0.03 mmol, 15 mol%), photocatalyst (0.01 mol, 5 mol%), and Cs₂CO₃ (0.4 mmol, 2.0 equiv.) in DCE (2 mL) which was irradiated under Blue LED typically for 24 h; ^bIsolated yields based on 2a, the dr was around 1/1 for all cases, and the dr was determined by ¹H NMR; ^cThe reaction was conducted without N₂ protection; ^d1 mmol scale; ^eK₂CO₃ as a base; ^ftriethylamine as a base; ^gDBU as a base. CDI: 1,1’-carbonyldiimidazole DBU; NHC: N-Heterocyclic carbene.