کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
5219557 1383360 2012 7 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Ligand design for dual enantioselective control in Cu-catalyzed asymmetric conjugate addition of R2Zn to cyclic enone
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی آلی
پیش نمایش صفحه اول مقاله
Ligand design for dual enantioselective control in Cu-catalyzed asymmetric conjugate addition of R2Zn to cyclic enone
چکیده انگلیسی

A new chiral N-heterocyclic carbene (NHC) ligand derived from a natural α-aminoester has been designed and synthesized. The coupling of N-methylbenzimidazole with an α-chloroacetamide derivative, which was prepared from chloroacetyl chloride and (S)-serine methyl ester, gave the corresponding ester/amide-functionalized azolium compound 20. The reaction of 2-cyclohexen-1-one (17) with Et2Zn in the presence of catalytic amounts of Cu(OTf)2 and 20 produced (R)-3-ethylcyclohexanone (18) as a major product. In contrast, the enantioselective conjugate addition (ECA) reaction catalyzed by Cu(OTf)2 under the influence of a hydroxy-amide-functionalized azolium compound 15, which was derived from (S)-tert-leucinol, produced (S)-18 in preference to (R)-18. A series of azolium salts were synthesized from (S)-serine esters, and the reaction conditions for the ECA reaction were optimized to produce (R)-18 with 69% ee. The best results were obtained in the case of the reaction of 4,4-dimethyl-2-cyclohexen-1-one (34) with Et2Zn catalyzed by Cu(OTf)2 in combination with azolium compounds. When the reaction of 34 with Et2Zn was carried out in the presence of catalytic amounts of Cu(OTf)2 and 20, (S)-3-ethyl-4,4-dimethylcyclohexanone (35) was obtained with 97% ee, whereas the ECA reaction under the influence of hydroxy-amide-functionalized azolium 15 afforded (R)-35 with >99% ee. In this manner, the reversal of enantioselectivity was achieved by controlling the structure of chiral ligands.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Tetrahedron - Volume 68, Issue 17, 29 April 2012, Pages 3512-3518
نویسندگان
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