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Catalytic annulation of heterocycles via a novel redox process involving the imidazolium salt N-heterocyclic carbene couple

Normand, Adrien, Yen, Swee Kuan, Huynh, Han Vinh, Hor, T. S. Andy and Cavell, Kingsley John 2008. Catalytic annulation of heterocycles via a novel redox process involving the imidazolium salt N-heterocyclic carbene couple. Organometallics 27 (13) , pp. 3153-3160. 10.1021/om800140n

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Abstract

A novel atom-efficient catalytic reaction, which converts imidazolium salts, with N-butenyl, N-substituted butenyl, and N-pentenyl substituents, into five- and six-membered fused-ring imidazolium and thiazolium salts has been developed. The reaction proceeds through azolium, C2−H, oxidative addition to Ni(0) followed by intramolecular insertion of the N-alkenyl double bond into the Ni hydride to give an intramolecularly bound carbene−Ni−alkyl intermediate. Reductive elimination of the linked carbene and alkyl groups gives the fused-ring azolium products and regenerates the Ni(0) catalyst. Products are potential building blocks for the synthesis of pharmaceuticals and novel ionic liquids. For example, 1,7-dimethyl-6,7-dihydro-5H-pyrrole[1,2-α]imidazolium bromide (2f), a five-membered fused-ring imidazolium salt, is formed from the catalytic ring closing of 1-butenyl-3-methylimidazolium bromide (1f). The reaction proceeds at moderate temperatures (50 °C) to give the products in high yield and selectivity. The catalyst was formed in situ from Ni(COD)2 plus added ligand L (where L = IMes, SMes, IPr, SPr, 4,5-Me2IPr, PPh3, PCy3, PCy2(Biphenyl), PtBu3) in DMF.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Cardiff Catalysis Institute (CCI)
Subjects: Q Science > QD Chemistry
Publisher: American Chemical Society
ISSN: 0276-7333
Last Modified: 02 Jan 2018 21:26
URI: http://orca-mwe.cf.ac.uk/id/eprint/6085

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