Synthesis of chiral salalen ligands and their in-situ generated Cu-complexes for asymmetric Henry reaction
作者:Ashish Dixit、Pramod Kumar、Surendra Singh
DOI:10.1002/chir.23019
日期:2018.12
Chiral salalen ligands derivedfrom (S)‐proline and derivatives of salicyaldehydes were synthesized, and their in‐situ generated Cu (II) complexes were evaluated in the asymmetric Henry reaction. Salalen ligand of different substituents on the phenyl moiety showed remarkable effect on the enantioselectivity of nitro‐aldol product of 4‐nitrobenzaldehyde and nitromethane. Cu (II) complex generated in
合成了衍生自(S)-脯氨酸和水杨醛衍生物的手性Salalen配体,并在不对称Henry反应中评估了它们原位生成的Cu(II)配合物。苯基部分上不同取代基的Salalen配体对4-硝基苯甲醛和硝基甲烷的硝基羟醛产物的对映选择性表现出显着影响。与(S)-2-(叔丁基)-6(((2-((((2-羟基-3-甲基苄基)氨基)甲基)吡咯烷烃-1-基)甲基)生成的Cu(II)络合物苯酚(10 mol%)和Cu(OAc)2 .H 2O(10 mol%)被发现是4-硝基苯甲醛与硝基甲烷之间硝基-羟醛反应的较好催化剂,40小时后,在35°C下,异丙醇中的相应产物收率为85%,对映体过量(ee)为88%。还以不同的取代的苯甲醛用于亨利反应的催化剂和相应的产物以22%至99%的产率和66%至92%的ee获得。4-硝基苯甲醛与前手性硝基乙烷的亨利反应产生抗选择性产物(dr = 79/21; anti / syn),收率为91%,ee为80%。
d-Mannitol-derived novel chiral thioureas: Synthesis and application in asymmetric Henry reactions
作者:Miaoxi Liu、Nan Ji、Li Wang、Peng Liu、Wei He
DOI:10.1016/j.tetlet.2018.01.082
日期:2018.3
Five novel thioureas have been obtained through multi-step reactions from d-Mannitol as starting material and applied as catalysts in the asymmetric Henry reaction. Using catalyst 7a, (1S,2R)-2-nitro-1-phenylpropan-1-ol containing two chiral centers was obtained in high yield and with high selectivity (up to 95% yield, 87% ee, 91:9 dr). This catalyst also retained activity in the presence of water
An efficient method for the synthesis of β-nitro alcohols from nitro alkanes and aldehydes in aqueous phosphate buffer under neutral pH conditions at room temperature is reported. In the case of higher nitro alkanes, the reaction showed very good diastereoselectivity to give syn β-nitro alcohols in preference to their anti products.
A new series of Schiff bases derived from Cinchona alkaloids were developed as chiral ligands for the copper(II)-catalyzed asymmetricHenry reaction. The optimized catalyst can promote the Henry reaction of both aromatic and aliphatic aldehydes with nitromethane or nitroethane. Those reactions can afford the chiral β-nitro alcohol adducts with high enantioselectivities.
Abstract Single chiral center C1 symmetric salalen and salan ligands were synthesized from (S)-proline and their Cu(II) complexes were used as catalysts for the asymmetricHenryreaction between aromatic aldehydes and nitromethane/nitroethane. The reaction of 4-nitrobenzaldehyde and nitromethane using salalen ligand (10 mol%) and Cu(OAc)2·H2O (10 mol%) in isopropanol with 4-methoxyphenol (10 mol%)