Boosting Conjugate Addition to Nitroolefins Using Lithium Tetraorganozincates: Synthetic Strategies and Structural Insights
Boosting Conjugate Addition to Nitroolefins Using Lithium Tetraorganozincates: Synthetic Strategies and Structural Insights
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DOI：
10.1002/chem.202001294
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发表时间：
2020-06-29
影响因子：
4.3
通讯作者：
Capriati, Vito
中科院分区：
文献类型：
--
作者：
Dell'Aera, Marzia;Perna, Filippo Maria;Capriati, Vito
我们报告了第一个无过渡金属催化剂和无配体的四有机锌酸锂（R4ZnLi2）与硝基烯烃的共轭加成。均配脂肪族和芳香族 R(4)ZnLi(2) 具有增强的亲核性以及独特的化学选择性和官能团耐受性，可在温和条件（0 ℃）和短反应时间（30 分钟）下以高达 98% 的收率获得有价值的硝基烷烃。当使用β-硝基丙烯酸酯和β-硝基烯酮时，这一点尤其显着，尽管存在其他亲电基团，但优选选择性1,4加成至C=C。结构和光谱研究证实了溶液中四有机锌酸盐的形成，其性质一直是一个长期争论的问题，并揭示了供体添加剂在这些试剂的聚集和结构中发挥的关键作用。因此，虽然螯合 N,N,N',N'-四甲基乙二胺 (TMEDA) 和 (R,R)-N,N,N',N'-四甲基-1,2-二氨基环己烷 (TMCDA) 有利于形成接触离子对锌酸盐，但大环路易斯供体 12-crown-4 会触发 Et(4)ZnLi(2) 立即歧化成等摩尔量的溶剂分离的 Et3ZnLi 和 EtLi。
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 R(4)ZnLi(2)provide access to valuable nitroalkanes in up to 98 % yield under mild conditions (0 degrees C) and short reaction time (30 min). This is particularly remarkable when employing beta-nitroacrylates and beta-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 chelatingN,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 Et3ZnLi and EtLi.