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Relevant academic research and scientific papers

Conjugate Addition of Organozinc Compounds to Nitroolefins

Symmetrical (R2Zn) or mixed diorganozinc compounds (R 1ZnR2) smoothly react with a series of nitroolefins in the presence of catalytic amounts of copper(I) salts and provide synthetically versatile nitro compounds in moderate to good yields. Simple alkyl groups, functionalized residues, or mixed trimethylsilylmethyl organozinc compounds (TMSM)ZnR may be employed for conjugate addition, while the TMSM group is not being transferred. ipso-Substitution is observed in absence of the copper(I) salt. Enantiomerically pure copper(I) complexes with BINOL based chiral phosphoramidite ligands efficiently catalyze the addition of dialkylzinc compounds to nitroalkenes. For instance, diethylzinc addition occurs with high yields and excellent enantioselectivity. Nitrostyrene, 3-nitroacrolein dimethylacetal, and 3-nitroacrylates have been used as substrates. The nitroolefin moiety predominates over the acrylate moiety and acts as the more powerful Michael acceptor. 2-Alkyl-3-nitropropanoates are exclusively obtained with excellent yield and enantioselectivity. The products can easily be transformed into β2-homoamino acids, compounds of high relevance for different areas of preparative organic chemistry.

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 (R4ZnLi2) to nitroolefins. Displaying enhanced nucleophilicity combined with unique chemoselectivity and functional group tolerance, homoleptic aliphatic and aromatic R4ZnLi2 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 Et4ZnLi2 into equimolar amounts of solvent-separated Et3ZnLi and EtLi.

Conjugate addition of mixed diorganozinc compounds and functionalized organozinc cuprates to nitroolefins

equation presented The copper-catalyzed conjugate addition of symmetrical and mixed diorganozinc compounds as well as functionalized diorganozinc cuprates to nitroolefins leads to synthetically versatile nitro compounds in moderate to good yields. Mixed TMSM-organozinc compounds are suitable reagents for conjugate addition, since the TMSM group is not being transferred. Ipso substitution is observed in the absence of a catalytic amount of copper(I) salt. The nitroalkene moiety in 3-nitroacrylates proved to be the predominant Michael acceptor.

Additions of organomanganese reagents to conjugated nitroolefins

Additions of organomanganese reagents to aromatic and aliphatic conjugated nitroolefins were examined for the first time. In most cases reaction proceeded rapidly at -30°C. Unlike Mn reagents lacking β-hydrogens (Me, Ph), which lead to oxidative coupling and reductive dimerisation of nitrostyrenes, benzylmanganese chloride gives 1,4-addition in yields exceeding Grignard or Cu-assisted additions. At 0°C alkyl(Bu, Pr)-manganese reagents undergo an addition-migration-elimination process with nitrostyrenes providing a convenient and stereospecific entry into arylated trans-olefins.