Combined experimental and computational investigations of rhodium-catalysed C-H functionalisation of pyrazoles with alkenes

Andrés G. Algarra, David L. Davies, Qudsia Khamker, Stuart A. Macgregor, Claire L. McMullin, Kuldip Singh, Barbara Villa-Marcos

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Abstract

Detailed experimental and computational studies have been carried out on the oxidative coupling of the alkenes C2H3Y (Y = CO2Me (a), Ph (b), C(O)Me (c)) with 3-aryl-5-R-pyrazoles (R = Me (1a), Ph (1b ), CF3 (1c)) using a[Rh(MeCN)3Cp∗][PF6]2/Cu(OAc)2·H2O catalyst system. In the reaction of methyl acrylate with 1a, up to five products (2aa-6aa) were formed, including the trans monovinyl product, either complexed within a novel CuI dimer (2aa) or as the free species (3aa), and a divinyl species (6aa); both 3aa and 6aa underwent cyclisation by an aza-Michael reaction to give fused heterocycles 4aa and 5aa, respectively. With styrene, only trans mono- and divinylation products were observed, whereas with methyl vinyl ketone, a stronger Michael acceptor, only cyclised oxidative coupling products were formed. Density functional theory calculations were performed to characterise the different migratory insertion and β-H transfer steps implicated in the reactions of 1a with methyl acrylate and styrene. The calculations showed a clear kinetic preference for 2,1-insertion and the formation of trans vinyl products, consistent with the experimental results.

Original languageEnglish
Pages (from-to)3087-3096
Number of pages10
JournalChemistry - A European Journal
Volume21
Issue number7
DOIs
Publication statusPublished - 9 Feb 2015

Keywords

  • C-H activation
  • Coupling reactions
  • Density functional calculations
  • Reaction mechanisms
  • Rhodium

ASJC Scopus subject areas

  • Chemistry(all)

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