Catalytic asymmetric benzoylation of 1,2-diols has been developed using a solid-phase asymmetric catalyst. The reaction conditions were optimized by the screening of different metal salts, solvents, bases, and temperatures. High-throughput screening was performed using circular dichroism detection, and the results revealed that Nb-imidazoline-copper(I) in combination with diisopropylethylamine was able to catalyze with high enantioselectivity, giving the monobenzoylated products in high yields and excellent enantiomeric excesses of up to 95% ee. [reaction: see text]
A chiral nitrogen-tethered bis (imidazoline) ligand (Nbimidazoline) was newly designed and synthesized in a divergent strategy. Thus, a single coupling reaction of primary amine with two molecules of chloromethylated imidazoline provided the Nbimidazoline. The copper(II) triflate complex of Nb-imidazoline catalyzed a trans-selective cyclopropanation of styrene with ethyl diazoacetate to give the adduct in high chemical yield with good enantiomeric excess up to 83%.
Carboxylic acid esters Q 0530Kinetic Resolution of 1,2-Diols Using Nitrogen-Tethered Bisimidazoline-Copper(I) Catalyzed Benzoylation. -The resolution of racemic diols (I) proceeds with moderate enantioselectivity. Although the benzoylated alcohol (IV) is the minor product, it records higher enantioselectivities than major product (III). However, conducting the experiments with the sterically hindered benzoyl chloride (V) improves the stereoselectivity essentially. -(ARAI*, T.; MIZUKAMI, T.; MISHIRO, A.; YANAGISAWA, A.; Heterocycles 76 (2008) 2, 995-1000; Dep. Chem., Fac. Sci., Chiba Univ., Inage, Chiba 263, Japan; Eng.) -H. Hoennerscheid 18-091
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