Another Offspring From Catalyst Union

Combining organic catalysis and photo­redox catalysis continues to bear fruit for chemists. Princeton University’s David W. C. MacMillan and James D. Cuthbertson report that using an iridium photocatalyst and a thiol organocatalyst together allows them to directly add aryl groups to allylic sp³ C–H bonds (Nature 2015, DOI: 10.1038/nature14255). MacMillan’s group has previously used the catalyst combo to asymmetrically alkylate aldehydes, enantioselectively α-trifluoromethylate aldehydes, and β-arylate aldehydes and ketones. The new reaction (shown) gives chemists an easy way to tack electron-deficient aromatic nitriles onto olefins, which could come in handy for making many types of molecules. The reaction works by linking two catalytic cycles. The photoredox catalyst turns the aromatic nitrile into a persistent radical by transferring an electron. At the same time, the thiol organocatalyst abstracts an allylic hydrogen atom from the olefin to create a radical. The two radicals then meet up to form the product.