Boosting Conjugate Addition to Nitroolefins Using Lithium Tetraorganozincates: Synthetic Strategies and Structural Insights

We report the first transition metal catalyst‐ and ligand‐free conjugate addition of lithium tetraorganozincates (R 4 ZnLi 2 ) to nitroolefins. Displaying enhanced nucleophilicity combined with unique chemoselectivity and functional group tolerance, homoleptic aliphatic and aromatic R 4 ZnLi 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 4 ZnLi 2 into equimolar amounts of solvent‐separated Et 3 ZnLi and EtLi.