Modified Heck Reaction With Remote Control

Nobel Laureate Richard Heck’s legacy stretches far into synthesis. Now, researchers have made his namesake reaction go to new lengths. The adapted Heck reaction forms a chiral carbon center while also acting several bonds away to oxidize an alcohol to a ketone (Science, DOI: 10.1126/science.1229208). Erik W. Werner and Matthew S. Sigman sought a reliable version of a phenomenon that sometimes happens in Heck chemistry—midreaction, the palladium catalyst migrates one carbon over, generating a ketone instead of the typical alkene. With colleagues at the University of Utah, they surmised that an electron-poor catalyst with bulky ligands might induce enantioselectivity, but the catalyst might also stick to an alkene substrate and walk along its carbon chain, adding ketone functionality two, three, or four carbons away from the reaction’s starting point. With aryldiazonium salts as arene sources, and pyridine-oxazoline ligands, they indeed obtained remotely functionalized chiral ketones. Next, Sigman says, the team must verify how the catalyst works and move toward more commonly used arene sources. Sigman used his own mathematical technique to find the ligand, and he needed only nine starting candidates instead of the typical hundreds—an impressive feat for an extremely challenging reaction, says University of Delaware organometallic chemist Donald A. Watson.