A general approach to intermolecular carbonylation of arene C–H bonds to ketones through catalytic aroyl triflate formation

The development of metal-catalysed methods to functionalize inert C–H bonds has become a dominant research theme in the past decade as an approach to efficient synthesis. However, the incorporation of carbon monoxide into such reactions to form valuable ketones has to date proved a challenge, despite its potential as a straightforward and green alternative to Friedel–Crafts reactions. Here we describe a new approach to palladium-catalysed C–H bond functionalization in which carbon monoxide is used to drive the generation of high-energy electrophiles. This offers a method to couple the useful features of metal-catalysed C–H functionalization (stable and available reagents) and electrophilic acylations (broad scope and selectivity), and synthesize ketones simply from aryl iodides, CO and arenes. Notably, the reaction proceeds in an intermolecular fashion, without directing groups and at very low palladium-catalyst loadings. Mechanistic studies show that the reaction proceeds through the catalytic build-up of potent aroyl triflate electrophiles. Catalytic transformations that incorporate carbonyl functional groups in arene C–H bonds have remained limited, despite being attractive synthetic steps. Now, the intermolecular carbonylative coupling of a broad range of simple arenes into ketones has been developed. The reaction occurs through the palladium-catalysed generation of high-energy aroyl triflate electrophiles.