This Review describes the development of strategies for carbonyl−olefin metathesis reactions relying on stepwise, stoichiometric, or catalytic approaches. A comprehensive overview of currently available methods is provided starting with Paterno−Buchi cycloadditions between carbonyls and alkenes, followed by fragmentation of the resulting oxetanes, metal alkylidene-mediated strategies, [3 + 2]-cycloaddition approaches with strained hydrazines as organocatalysts, Lewis acid-mediated and Lewis acidcatalyzed strategies relying on the formation of intermediate oxetanes, and protocols based on initial carbon−carbon bond formation between carbonyls and alkenes and subsequent Grob-fragmentations. The Review concludes with an overview of applications of these currently available methods for carbonyl−olefin metathesis in complex molecule synthesis. Over the past eight years, the field of carbonyl−olefin metathesis has grown significantly and expanded from stoichiometric reaction protocols to efficient catalytic strategies for ring-closing, ring-opening, and cross carbonyl− olefin metathesis. The aim of this Review is to capture the status quo of the field and is expected to contribute to further advancements in carbonyl−olefin metathesis in the coming years.9396 7.2. Cross Carbonyl−Olefin Metathesis 9396 8. Applications in Natural Product Synthesis 9398 9.

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A nonfunctionalized bis­(imidazole) ligand precursor has been directly metalated using IrCp*­(OAc)2, leading to a mixture of bis­(protic N-heterocyclic carbene) (bisPNHC) complexes (2a,b). Treatment of 2a,b with HCl gas in CH2Cl2 gave a bisPNHC complex (3a), which has been transformed into a hydride bisPNHC complex. Complex 3a underwent ligand and counterion exchange reactions to afford acetonitrile and ethylamine bisPNHC complexes (5 and 6). Furthermore, these bisPNHC complexes have been tested as catalysts in transfer hydrogenation reactions of ketones and unsaturated ketones.

We describe the development of a new catalyst system for carbonyl-olefin ring-closing metathesis reactions that relies on Lewis acidic superelectrophiles and significantly expands the current scope of this transformation to medium-sized rings. <div>Importantly, these superelectrophiles are shown to promote carbonyl-olefin metathesis via a distinct and unprecedented mechanism. </div>

We describe the development of a new catalyst system for carbonyl-olefin ring-closing metathesis reactions that relies on Lewis acidic superelectrophiles and significantly expands the current scope of this transformation to medium-sized rings. <div>Importantly, these superelectrophiles are shown to promote carbonyl-olefin metathesis via a distinct and unprecedented mechanism. </div>