Figure 2. Scope of the enantioselective catalytic [2+2] cycloaddition of 2′-hydroxychalcones.

Data reflect the averaged isolated yields from two reproducible experiments. Diastereomer ratios were determined by ¹H NMR analysis of the unpurified reaction mixture. Enantiomer ratios were determined using chiral SFC or HPLC analysis. See supplementary material for details. ^* Irradiation was conducted using a blue LED lamp instead of a 23 W CFL bulb, 2 h irradiation time. ^† 40 h irradiation time. ^‡Isolated as a 6:1 mixture of regioisomers.