Cycloaddition Chemistry of Fulvenes and Derivatives

Fulvenes are a distinctive class of five-membered conjugated hydrocarbons characterised by an exocyclic methylene group conjugated to a cyclopentadienyl ring. Their non‐benzenoid electronic structure confers pronounced reactivity in pericyclic processes, notably cycloadditions, in which fulvenes can act as electron-rich dienes, dipolarophiles or 4π components. This versatility has been harnessed for the synthesis of complex polycyclic architectures, including natural product frameworks and novel materials. In intramolecular and intermolecular settings, fulvene cycloadditions proceed under mild thermal or photochemical conditions, often with high regio- and stereocontrol. Recent advances have expanded the scope of fulvene cycloadditions beyond traditional Diels–Alder and [2+2] processes to include [4+3] and dipolar cycloadditions, enabling direct access to diverse carbocyclic and heterocyclic scaffolds. The interplay between substituent electronics, ring strain and dipolar resonance underpins the selectivity of these transformations. Applications now extend into dynamic combinatorial chemistry, materials science and ligand design for organometallic catalysis, demonstrating the global significance of fulvene-based cycloaddition strategies in modern synthetic chemistry.

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Cycloaddition Chemistry of Fulvenes and Derivatives publication trend

The graph below shows the total number of articles in cycloaddition chemistry of fulvenes and derivatives across all publications each year (not limited to Nature Index journals).

Technical terms

Fulvene: A conjugated five-membered ring system bearing an exocyclic methylene, notable for its non-benzenoid resonance and reactivity in pericyclic reactions.

Cycloaddition: A pericyclic reaction in which two or more unsaturated fragments combine to form a cyclic adduct with concurrent bond formation.

Diels–Alder reaction: A [4+2] cycloaddition between a conjugated diene and a dienophile, widely employed in ring construction.

Michael annulation: A base-catalysed sequence involving a Michael addition followed by intramolecular cyclisation to form cyclic products.

Dipolar resonance: The description of a molecule in which canonical forms exhibit significant charge separation, influencing reactivity toward cycloaddition partners.

References

1. An overview of the cycloaddition chemistry of fulvenes and emerging applications. Beilstein Journal of Organic Chemistry (2019).
2. Connect Four: Tetraarylated Dihydropentalenes and Triarylated Monocyclic Pentafulvenes from Cyclopentadienes and Enones. The Journal of Organic Chemistry (2022).