New Reactivity Modes between Carbonyls and Olefins: Catalytic Carbonyl-Olefin Metathesis and Oxygen Atom Transfer

Abstract

The development of sustainable and selective catalytic procedures for carbon-carbon and carbon-heteroatom bond formation is of the utmost importance to the field of synthetic organic chemistry. Such methods are essential for the synthesis of complex and biologically active molecules, including functional materials and current pharmaceuticals. Some of the simplest and most powerful existing carbon-carbon and carbon-heteroatom bond forming strategies take advantage of divergent reactivity and rely on readily accessible functional groups: carbonyls and olefins. Herein is described the development of sustainable and selective Lewis and Brønsted acid-catalyzed methods to rapidly access complex, carbocyclic frameworks relying on carbonyl and olefin functional handles. These methods serve as mild alternatives to currently available reaction protocols and are characterized by their operational simplicity and distinct reaction mechanisms. In particular, we are able to report robust, catalytic methods for the synthesis of 3,4-dihydro-2H-pyrans and tetrahydronaphthalenes relying on FeCl3 as a benign and earth-abundant transition metal catalyst. Additionally, we report the interrupted carbonyl-olefin metathesis reaction as a new acid-catalyzed mode of reactivity between carbonyl and olefin functionalities for the synthesis of tetrahydrofluorenes. Importantly, this method complements the repertoire of well-established reactions between carbonyls and olefins and relies on TfOH as an inexpensive catalyst. Furthermore, the development of new catalysts for carbonyl-olefin metathesis, a previously established and powerful method for the synthesis of carbon-carbon bonds, is described. Previously inaccessible six-membered alkene ring systems are now obtainable as metathesis products utilizing heterobimetallic ion pairs, while previously overreactive products arising from bis-alkene substrates can be synthesized utilizing iron-based cationic complexes. We expect these findings to lead to further developments with respect to catalyst design for the expansion of scope of carbonyl-olefin metathesis.