Carbene-Mediated Synthetic Strategies in Organic Chemistry

Carbenes, neutral species bearing a divalent carbon atom with two nonbonded electrons, have emerged as versatile intermediates in modern organic synthesis. Their unique electronic structure enables multiple reaction pathways, including cyclopropanation of alkenes, insertion into C–H or X–H bonds, ylide formation with heteroatoms and umpolung reactivity via nucleophilic carbenoids. Transition‐metal complexes—most commonly those of rhodium, copper or iron—stabilise reactive carbenes and guide selectivity through ligand design, delivering high levels of enantio‐ and regioselectivity. In parallel, stable N-heterocyclic carbenes (NHCs) serve as organocatalysts or ligands that mediate umpolung of carbonyl compounds, enabling bond constructions inaccessible by classical two‐electron pathways. Photochemical generation of donor–acceptor carbenes under visible light has further expanded the toolkit, allowing mild, site‐selective C–H and C–C bond formation in complex settings. Together, these strategies have found applications in the total synthesis of natural products, late‐stage functionalisation of pharmaceuticals and the rapid assembly of diverse molecular scaffolds for materials science. Recent advances emphasise sustainable conditions—reduced catalyst loadings, renewable feedstocks and ambient‐temperature processes—underscoring the global significance of carbene‐mediated methods for both academic research and industrial manufacture.

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Carbene-Mediated Synthetic Strategies in Organic Chemistry publication trend

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Technical terms

Carbene: A neutral intermediate featuring a divalent carbon atom with two nonbonded electrons, capable of multiple bond‐forming reactions.

Metal–carbene: A carbene bound to a transition metal centre, whose reactivity and selectivity are modulated by the metal and its ligands.

N-heterocyclic carbene (NHC): A stable carbene embedded in a heterocyclic framework, widely used as an organocatalyst or ligand in synthesis.

Donor–acceptor carbene: A carbene substituted simultaneously by electron‐donating and electron‐withdrawing groups, which stabilise the reactive centre and tune selectivity.

Cyclopropanation: The addition of a carbene to an alkene, forming a three‐membered cyclopropane ring.

C–H insertion: A reaction in which a carbene inserts into a C–H bond to form a new C–C linkage.

Ylide: A zwitterionic species formed by reaction of a carbene with a heteroatom (e.g. oxygen or phosphorus), often a key intermediate in cycloaddition and rearrangement reactions.

References

1. Cycloadditionen von Diazoalkenen mit P4 und tBuCP: Ein Zugang zu Diazaphospholen. Angewandte Chemie (2024).
2. Enantioselective intramolecular 1,3-dipolar cycloadditions of diazocarbonyl-derived oxidopyryliums. Arkivoc (2003).