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.