Initially, the three-component reaction of 1-methylquinoxalin-2(1
H)-one (
1a), styrene (
2a) and benzenesulfinic acid (
3) was chosen as model reaction to optimize the reaction conditions. The initial reaction was performed in CH
3CN by the irradiation of 3 W blue LED lamps at room temperature using 4CzIPN (1, 2, 3, 5-tetrakis (carbazol-9-yl)-4, 6-dicyanobenzene) as photocatalyst (2 mol%). To our delight, the corresponding product
4a would be obtained in 54% yield (
Table 1, entry 1). Subsequently, a number of solvents were examined, and replacement of CH
3CN with ether such as DME, THF or 1, 4-dioxane gave a significantly decreased yield (
Table 1, entries 2–4). Halogenated solvents such as CHCl
3 and 1, 2-dichloroethane (DCE) afforded the good reaction efficiency, and DCE was elicited as the best mediator for the reaction (
Table 1, entry 5). By contrast, the relatively lower yields were observed when dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were used as the reaction solvents (
Table 1, entries 7 and 8). Next, the catalytic activities of various photocatalysts were investigated (
Table 1, entries 9–14). In addition to 4CzIPN, other photocatalysts such as Eosin Y, Na
2-Eosin Y, rhodamine B, Ru(bpy)
3Cl
2·3H
2O, or Mes-Acr
+ClO
4− can also promote the reaction, but each of them was less effective than 4CzIPN. A screen of the amount of photocatalyst revealed that 2 mol% of 4CzIPN was the best choice, the decrease or increase of 4CzIPN loading would lead to the lower yields (
Table 1, entries 15 and 16). In addition, a critical survey of light source showed that blue LED was the best-supporting light source, other light sources such as green or white LED only gave the desired product
4a in moderate yields (
Table 1, entries 17 and 18). When the reaction was carried out under N
2 or O
2, and the product
4a was obtained in 73% and 46%, respectively (
Table 1, entries 19 and 20). Control experiments without either photocatalyst or light were performed to show that this transformation did not occur at all (
Table 1, entries 21 and 22).