Fulvenes
Fulvenes are the class of hydrocarbon obtained by formally cross-conjugating one ring and methylidene through a common exocyclic double bond.[1][2]
In addition to compounds with substituent group on the fulvene skeleton, structural analogs in this class include heteroatom replacements[3] and variations of ring-size. Thus, methylenecyclopropene can be called triafulvene and cyclopropenone is an oxafulvene.[4] Analogs in which certain ring carbons are replaced by other elements, sometimes entailing changes of the double-bonding pattern of the heterocyclic core as in dithiafulvene, lead to changes in the electronic properties of the ring.[5]
Preparation
[edit]Fulvenes are readily prepared by the condensation of cyclopentadiene with various aldehydes and ketones under strongly basic conditions, via a cyclopentadienyl anion intermediate:
- C5H6 + R2C=O → C4H4C=CR2 + H2O
Johannes Thiele is credited with discovering this reaction.[6][7]
Modern synthesis of fulvenes employ buffer systems or other mild conditions.[8][9]
Properties
[edit]The cross-conjugation generally destabilizes the exocyclic double bond, as (per Hückel's rules) polarization of the π electrons would lead to an aromatic ring ion. Consequently, fulvenes add nucleo- and electrophiles easily. They also have a small HOMO–LUMO gap, typically leading to the eponymous visible coloration ("fulvus" is Latin for "yellow").[10]
Ligand in organometallic chemistry
[edit]Fulvenes are common ligands and ligand precursors in organometallic chemistry.[11] 2,3,4,5-Tetramethylfulvene, abbreviated Me4Fv, results from the deprotonation of cationic pentamethylcyclopentadienyl complexes.[12] Some Me4Fv complexes are called tuck-in complexes.
References
[edit]- ↑ Agranat, Israel (2012), "Ground-State Versus Excited-State Polarity of Triafulvenes: A Study of Solvent Effects on Molecular Electronic Spectra", The Jerusalem Symposia on Quantum Chemistry and Biochemistry, vol. 8, pp. 573–583, doi:10.1007/978-94-010-1837-1_36, ISBN 978-94-010-1839-5
- ↑ Neuenschwander, Markus (1986), "Synthetic and NMR spectroscopic investigations of fulvenes and fulvalenes" (PDF), Pure Appl. Chem., 58 (1): 55–66, doi:10.1351/pac198658010055
- ↑ IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "Fulvenes". doi:10.1351/goldbook.F02550
- ↑ Kawase, Takeshi; Kurata, Hiroyuki (2016). "Recent Developments in Fulvene and Heterofulvene Chemistry". Cross Conjugation. pp. 145–248. doi:10.1002/9783527671182.ch6. ISBN 978-3-527-33437-7.
- ↑ Schøttler, Christina; Lund-Rasmussen, Kasper; Broløs, Line; Vinterberg, Philip; Bazikova, Ema; Pedersen, Viktor B R.; Nielsen, Mogens Brøndsted (2024). "Multi-redox indenofluorene chromophores incorporating dithiafulvene donor and ene/Enediyne acceptor units". Beilstein Journal of Organic Chemistry. 20: 59–73. doi:10.3762/bjoc.20.8. PMC 10804541. PMID 38264453.
- ↑ Thiele, J. (1900). "Ueber Ketonreactionen bei dem Cyclopentadiën". Chemische Berichte. 33: 666–673. doi:10.1002/cber.190003301113.
- ↑ Hafner, K.; Vöpel, K. H.; Ploss, G.; König, C. (1967). "6-(Dimethylamino)Fulvene". Organic Syntheses. 47: 52. doi:10.15227/orgsyn.047.0052.
- ↑ Coşkun, Necdet; Erden, Ihsan (2011-11-11). "An efficient catalytic method for fulvene synthesis". Tetrahedron. 67 (45): 8607–8614. doi:10.1016/j.tet.2011.09.036. ISSN 0040-4020. PMC 3196336. PMID 22021940.
- ↑ Sieverding, Paul; Osterbrink, Johanna; Besson, Claire; Kögerler, Paul (2019-01-18). "Kinetics and mechanism of pyrrolidine buffer-catalyzed fulvene formation". J. Org. Chem. 84 (2): 486–494. doi:10.1021/acs.joc.8b01660. ISSN 0022-3263. PMID 30540466.
- ↑ Neuenschwander, M. (1989). "Fulvenes". In Patai, Saul (ed.). The Chemistry of Double-Bonded Functional Groups. The Chemistry of Functional Groups. Vol. Supplement A, Part 2. Wiley. pp. 1132–1136. doi:10.1002/9780470772256.ch4. ISBN 978-0-470-77225-6.
- ↑ Strohfeldt, Katja; Tacke, Matthias (2008). "Bioorganometallic fulvene-derived titanocene anti-cancer drugs". Chemical Society Reviews. 37 (6): 1174–87. doi:10.1039/B707310K. PMID 18497930.
- ↑ Kreindlin, A. Z.; Rybinskaya, M. A. (2004). "Cationic and Neutral Transition Metal Complexes with a Tetramethylfulvene or Trimethylallyldiene Ligand". Russian Chemical Reviews. 73 (5): 417–432. Bibcode:2004RuCRv..73..417K. doi:10.1070/RC2004v073n05ABEH000842.
