Werner Complexes with ω-Dimethylaminoalkyl Substituted Ethylenediamine Ligands: Bifunctional Hydrogen-Bond-Donor Catalysts for Highly Enantioselective Michael Additions.

Autor:	Ghosh, Subrata K., Ganzmann, Carola, Bhuvanesh, Nattamai, Gladysz, John A.
Předmět:	CARBONATE synthesis ETHYLENEDIAMINE RACEMIC mixtures NITROALKENES SUBSTITUENTS (Chemistry) HYDROGEN bonding MICHAEL reaction ASYMMETRIC synthesis
Zdroj:	Angewandte Chemie International Edition; 3/18/2016, Vol. 55 Issue 13, p4356-4360, 5p
Abstrakt:	The racemic carbonate complex [Co(en)2O2CO]+ Cl− (en=1,2-ethylenediamine) and ( S)-[H3NCH((CH2) nNHMe2)CH2NH3]3+ 3 Cl− ( n=1-4) react (water, charcoal, 100 °C) to give [Co(en)2(( S)-H2NCH((CH2) nNHMe2)CH2NH2)]4+ 4 Cl− ( 3 a- d H4+ 4 Cl−) as a mixture of Λ/Δ diastereomers that separate on chiral-phase Sephadex columns. These are treated with NaOH/Na+ BArf− (BArf=B(3,5-C6H3(CF3)2)4) to give lipophilic Λ- and Δ- 3 a-d3+ 3 BArf−, which are screened as catalysts (10 mol %) for additions of dialkyl malonates to nitroalkenes. Optimal results are obtained with Λ- 3 c3+ 3 BArf− (CH2Cl2, −35 °C; 98-82 % yields and 99-93 % ee for six β-arylnitroethenes). The monofunctional catalysts Λ- and Δ-[Co(en)3]3+ 3 BArf− give enantioselectivities of <10 % ee with equal loadings of Et3N. The crystal structure of Δ- 3 a H4+ 4 Cl− provides a starting point for speculation regarding transition-state assemblies. [ABSTRACT FROM AUTHOR]
Databáze:	Complementary Index
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