We recently reported a novel ester metathesis reaction where an unsymmetrical ester such as ethyl hexanoate can be transformed to a statistical mixture of starting material, hexyl ethanoate, ethyl acetate and hexyl hexanoate as expected from a metathesis reaction, with 0.2mol% of commercially available Ru catalyst. Although chemical metathesis has been observed for alkanes, alkenes and alkynes, to the best of our knowledge it has not been previously reported for the ester functionality. Extending the chemistry, we find that a 20x excess of low boiling alcohol ethanol, allows for the transfer of the acyl moiety to the sacrificial low boiling ethyl acetate product, while significantly increasing the functional group tolerance and substrate scope. Yields of alcohols can reach 90%, which represents an attractive alternative to current high H2 pressure hydrogenation protocols for Ru based ester reduction chemistry. Previous approaches to transfer hydrogenation of esters were unsuccessful due to the use of hydrogen donors (such as isopropanol) that did not sufficiently compensate for the thermodynamic cost of formation of a primary alcohol from the ester. Following up on this report we discovered a new mode of reactivity of esters with substrates that possess activated CH bonds. Accordingly, a new Ru(II) catalyzed cyclopropanation reaction that is conceptually different from previously reported cyclopropanation protocols that include Corey-Chaikovsky, Simmons-Smith, and metal catalyzed carbene attack on olefins will be reported.

Catalytic ester metathesis with applications to the transfer hydrogenation of esters, and the serendipitous discovery of a cyclopropanation of aliphatic esters and alcohols with a homogeneous Ru(II) catalyst

254th National Meeting (2017)

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