Boosting conjugate addition to nitroolefins using lithium tetraorganozincates: synthetic strategies and structural insights

Marzia Dell'Aera, Filippo Maria Perna, Paola Vitale, Angela Altomare, Alessandro Palmieri, Lewis C. H. Maddock, Leonie J. Bole, Alan R. Kennedy, Eva Hevia , Vito Capriati

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3 Citations (Scopus)

Abstract

We report the first transition metal catalyst- and ligand-free conjugate addition of lithium tetraorganozincates (R 4ZnLi 2) to nitroolefins. Displaying enhanced nucleophilicity combined with unique chemoselectivity and functional group tolerance, homoleptic aliphatic and aromatic R 4ZnLi 2 provide access to valuable nitroalkanes in up to 98 % yield under mild conditions (0 °C) and short reaction time (30 min). This is particularly remarkable when employing β-nitroacrylates and β-nitroenones, where despite the presence of other electrophilic groups, selective 1,4 addition to the C=C is preferred. Structural and spectroscopic studies confirmed the formation of tetraorganozincate species in solution, the nature of which has been a long debated issue, and allowed to unveil the key role played by donor additives on the aggregation and structure of these reagents. Thus, while chelating N,N,N',N'-tetramethylethylenediamine (TMEDA) and (R,R)-N,N,N',N'-tetramethyl-1,2-diaminocyclohexane (TMCDA) favour the formation of contacted-ion pair zincates, macrocyclic Lewis donor 12-crown-4 triggers an immediate disproportionation process of Et 4ZnLi 2 into equimolar amounts of solvent-separated Et 3ZnLi and EtLi.

Original languageEnglish
Pages (from-to)8742-8748
Number of pages7
JournalChemistry - A European Journal
Volume26
Issue number40
Early online date17 Mar 2020
DOIs
Publication statusPublished - 17 Jul 2020

Keywords

  • addition
  • arylation
  • lithium
  • nitroolefins
  • zincate

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    Dell'Aera, M., Perna, F. M., Vitale, P., Altomare, A., Palmieri, A., Maddock, L. C. H., Bole, L. J., Kennedy, A. R., Hevia , E., & Capriati, V. (2020). Boosting conjugate addition to nitroolefins using lithium tetraorganozincates: synthetic strategies and structural insights. Chemistry - A European Journal, 26(40), 8742-8748. https://doi.org/10.1002/chem.202001294