A Two-Catalyst Photochemistry Route to Homochiral Rings

Many biologically active compounds used in medicine and agriculture are still produced as a racemic mixture, even though only one isomer is actually active. The presence of the inactive isomer can lead to unwanted side effects. The efficient synthesis of only one stereoisomer—homochiral molecules—is a key goal in organic synthesis ( 1 ). Synthesizing homochiral molecules with light and a photocatalyst has been an unmet challenge for many years ( 2 ), yet the combination of light and catalysis to create chiral products is a hallmark of photosynthesis. On page 392 of this issue, Du et al. ( 3 ) report an efficient chiral selection by combining a transition-metal photocatalyst with a stereocontrolling cocatalyst. They obtained four-membered rings in good yields and with excellent enantioselectivity. This approach avoids the problems associated with the noncatalyzed background reaction, which hampers most photocatalytic processes.