Interrupted Carbonyl–Olefin Metathesis of Cyclic, Aliphatic Ketones

Functionalized pentalenes, indenes, naphthalenes and azulenes represent common structural motifs in many compounds of biological importance. We herein describe an iron-catalyzed synthetic strategy that enables access to these central scaffolds in two steps from commercial material. This method complements established transformations between carbonyl and olefin moieties, such as carbonyl–ene, Prins and carbonyl–olefin metathesis (COM) reactions as a fourth reactivity mode. Experimental and theoretical investigations support a mechanism that interrupts the carbonyl–olefin metathesis reaction pathway through the distinct fragmentation of intermediate oxetanes resulting in the direct formation of functionalized pentalenes, indenes, naphthalenes, and azulenes. The scope of this iron-catalyzed transformation between carbonyl and olefin functionalities is demonstrated with 19 examples proceeding in up to 99% yield.