Boosting Conjugate Addition to Nitroolefins Using Lithium Tetraorganozincates: Synthetic Strategies and Structural Insights. Issue 40 (29th June 2020)

• Record Type: Journal Article
• Authors: Dell'Aera, Marzia; Perna, Filippo Maria; Vitale, Paola; Altomare, Angela; Palmieri, Alessandro; Maddock, Lewis C. H.; Bole, Leonie J.; Kennedy, Alan R.; Hevia, Eva; Capriati, Vito
• Is Part Of: Chemistry. Volume 26:Issue 40(2020)
• Page Start: 8742
• Page End: 8748
• Publication Date: 2020-06-29
• Subjects: addition -- arylation -- lithium -- nitroolefins -- zincate; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202001294
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: We report the first transition metal catalyst‐ and ligand‐free conjugate addition of lithium tetraorganozincates (R4 ZnLi2 ) to nitroolefins. Displaying enhanced nucleophilicity combined with unique chemoselectivity and functional group tolerance, homoleptic aliphatic and aromatic R4 ZnLi2 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 Et4 ZnLi2 into equimolar amounts of solvent‐separated Et3 ZnLi and EtLi. Abstract : The metamorphosis of organozinc reagents ! Transforming neutral R2 Zn into nucleophilic R4 ZnLi2 zincate complexes enabled chemoselective alkylation/arylation of nitroolefins to give 1, 4‐addition adducts in up to 98 % yield. Structural and spectroscopic investigations confirmed the dianionic‐type nature of these species and the key role of donor additives in their aggregation and structure.