How chemists are harnessing halogen bonds for asymmetric synthesis

A long-overlooked mode of catalysis is finally going asymmetric. Halogen bonds were first proposed as an activating interaction in 2008, but this alternative flavour of organocatalysis was initially slow to gain traction among the organic community. General scepticism about their paradoxical nature, coupled with the difficulty of engineering an effective chiral catalyst led many to dismiss halogen-bond donors in favour of more established hydrogen bonding systems.

However, halogen-bond catalysis has quietly been undergoing a revolution. Deepening insights into this unusual non-covalent bond over the last 15 years have boosted the performance of many halogen bond systems well beyond the capabilities of conventional organocatalysts. And now, a flurry of asymmetric approaches are broadening the reach of halogen-bond catalysis even further, slowly bringing it to the mainstream as an alternative tool in organic synthesis.