Study On The Enantioselective Henry Reaction Of α-Ketoesters Catalyzed By Chiral Copper( Ⅱ )-Diamine Complex

The asymmertric Henry reaction ofα-ketoesters with nitromethane that provides straightforward access toβ-nitroα-hydroxy esters containing chiral quaternary carbon center represents a powerful C–C bond-forming tool, and the resulting multi-functional products can be transformed into compounds such asβ-aminoα-hydroxy esters,α-lactams and aziridines which are highly useful compounds in organic chemistry. However, there are only fourteen papers with regard to the catalytic asymmetric Henry reaction ofα-ketoesters since the first example that was reported by J?rgensen in 2001. Besides, most of the results in these papers are not so satisfactory with only moderate to good yields and enantioselectivities. Thus, opportunities as well as challenges triggered us to carry out the work. In this thesis, we delineate the development of the enantioselective Henry reaction ofα-keto esters with nitromethane catalyzed by copper (Ⅱ) salts in combination with chiral diamine ligands in the presence of base additives.Firstly, we chose the reaction of ethyl pyruvate with nitromethane as the model reaction to screen a series of C1 symmetric diamine ligands. It was found that ligands with two secondary amines were superior to other diamine ligands in terms of enantioselectivity and L7 gave the most promising result. To the best of our knowledge, no report has been made on Henry reaction ofα-ketoesters that was catalyzed by diamine ligands with two secondary amines.Secondly, optimizations of the reaction parameters were carried out systematically, such as metal salts, solvents, base additives and their amounts. The standard conditions were established as follows:α-ketoesters and nitromethane reacted in the presence of 20 mol% Cu(OTf)₂ in combination with 20 mol% L7 and 25 mol% N-methyl morpholine as base additive in solvent of CH₃NO₂ at 0℃. Finally, under the optimized reaction conditions, the scope of the reaction was investigated affording the corresponding products in 72-94% yield and e.e. up to 78%. Then the Henry adduct of ethyl pyruvate which was obtained at 0℃with 76% ee, was treated with cinnamaldehyde in the presence of catalytic (S)-2-diphenylprolinol, giving the corresponding substituted six-membered lactone with 82% ee. The lactone thus obtained represnts one of the most important building blocks in organic synthesis.