Beyond olefins: new metathesis directions for synthesis.

The olefin-olefin metathesis reaction has emerged as one of the most important carbon-carbon bond-forming reactions, as illustrated by its wide use in the synthesis of complex molecules, natural products and pharmaceuticals. The corresponding metathesis reaction between carbonyls and olefins or alkynes similarly allows for the formation of carbon-carbon bonds. Although these variants are far less developed and utilized in organic synthesis, they possess attractive qualities that have prompted chemists to incorporate and explore these modes of reactivity in complex molecule synthesis. This review highlights selected examples of carbonyl-olefin and carbonyl-alkyne metathesis reactions in organic synthesis, in particular in the total synthesis of natural products and complex molecules, and provides an overview of current advantages and limitations.