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.
The development of a Lewis acid-catalyzed ring-opening cross-metathesis reaction which enables selective access to acyclic, unsaturated ketones as the carbonyl-olefin metathesis products is described. While catalytic amounts of FeCl were previously identified as optimal to catalyze ring-closing metathesis reactions, the complementary ring-opening metathesis between cyclic alkenes and carbonyl functionalities relies on GaCl as the superior Lewis acid catalyst.
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<p>Herein, we describe the application of Lewis acid-catalyzed
carbonyl-olefin metathesis towards the synthesis of chiral, substituted
tetrahydropyridines from commercially available amino acids as chiral pool
reagents. This strategy relies on FeCl<sub>3</sub> as an inexpensive and
environmentally benign catalyst and enables access to a variety of substituted
tetrahydropyridines under mild reaction conditions. The reaction proceeds with
complete stereoretention and is viable for a variety of natural and unnatural
amino acids to provide the corresponding tetrahydropyridines in up to 99% yield.</p>
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An intermolecular carbonyl−olefin metathesis reaction is described that relies on superelectrophilic Fe(III)-based ion pairs as stronger Lewis acid catalysts. This new catalytic system enables selective access to (E)-olefins as carbonyl−olefin metathesis products. Mechanistic investigations suggest the regioselective formation and stereospecific fragmentation of intermediate oxetanes to be the origin of this selectivity. The optimized conditions are general for a variety of aryl aldehydes and trisubstituted olefins and are demonstrated for 28 examples in up to 64% overall yield.
Herein we describe the application of Lewis-acidcatalyzed carbonyl−olefin metathesis toward the synthesis of substituted tetrahydropyridines from commercially available amino acids as chiral pool reagents. This strategy relies on FeCl 3 as an inexpensive and environmentally benign catalyst and enables access to a variety of substituted tetrahydropyridines under mild reaction conditions. The reaction proceeds with complete stereoretention and is viable for a variety of natural and unnatural amino acids to provide the corresponding tetrahydropyridines in up to 99% yield.Letter pubs.acs.org/OrgLett
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