About-Face For Hydroformylations

The hydroformylation reaction, also known as the oxo process, is a key industrial route for converting alkenes, CO, and H₂ into aldehydes that serve as intermediates to make a variety of chemical products. Chemists have now figured out a way to turn the reaction around and undo hydroformylations under mild conditions without involving gaseous reagents, rendering aldehydes into alkene derivatives (Science 2015, DOI: 10.1126/science.1261232). Why anyone would want to do such a thing is not at first intuitive, but Stephen K. Murphy, Vy M. Dong, and colleagues of the University of California, Irvine, offer the method as a new option for modifying complex molecules in pharmaceutical research. For example, enzyme-mediated dehydroformylation of aldehydes to generate alkenes occurs during the biosynthesis of sterols such as cholesterol. The UC Irvine researchers thought they could mimic that process, but it required designing a transition-metal catalyst to trigger C–C bond cleavage by selective activation of the aldehyde C–H bond. Their rhodium(Xantphos)(benzoate) catalyst does that while transferring a formyl group and hydride from the aldehyde to an added strained olefin receptor such as norbornene. The team tested the reaction on a set of benzyl aldehydes as well as on conversion of the natural product stimulant (+)-yohimbine to (+)-yohimbenone.