Noji Masahiro, Konno Yosuke, Ishii Keitaro
Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan.
J Org Chem. 2007 Jul 6;72(14):5161-7. doi: 10.1021/jo0705216. Epub 2007 Jun 8.
The rare earth metal and hafnium triflate-catalyzed secondary benzylation and allylation of 1,3-diketones, ketoesters, and ketoamides are described. The procedure was carried out under non-anhydrous conditions. Various 1-phenylethyl cations were generated from substituted 1-phenylethanols using 0.5 mol % of the metal triflates in CH3NO2. The cations reacted with 1,3-diketones and ketoesters to give benzylated products in high yields. Following the GC analysis, the reaction conditions were easily optimized by the selection of catalysts based on the Lewis acidity of the triflates and reaction temperature. A tertiary-alkylated diketone and a corresponding ketoester were also benzylated to afford products with a quaternary carbon atom in 57-84% yield. The ketoamide reactions required stronger Lewis acids than those used in the diketone and ketoester reactions. The reactions of benzylic alcohols possessing various substituents on the aromatic ring and dibenzoylmethane (2b) as a diketone were examined in the presence of Hf(OTf)4. Electron-rich benzylic alcohols reacted with 2b in 86-96% yield, and electron-deficient alcohol gave the desired product in 79-65% yield. Despite possessing a strong electron-withdrawing group, the reaction of 1-(4-nitrophenyl)ethanol gave the corresponding product in 61% yield. It was also possible to use allylic alcohols directly for the allylation of diketone 2b. The catalyst can be recovered by water extraction and reused up to five times.
描述了稀土金属和三氟甲磺酸铪催化的1,3 - 二酮、酮酯和酮酰胺的二级苄基化和烯丙基化反应。该反应在非无水条件下进行。使用0.5 mol%的金属三氟甲磺酸盐在CH3NO2中，由取代的1 - 苯乙醇生成各种1 - 苯乙基阳离子。这些阳离子与1,3 - 二酮和酮酯反应，以高收率得到苄基化产物。通过气相色谱分析后，基于三氟甲磺酸盐的路易斯酸度和反应温度选择催化剂，可轻松优化反应条件。一种叔烷基化的二酮和相应的酮酯也进行了苄基化反应，得到具有季碳原子的产物，收率为57 - 84%。酮酰胺反应所需的路易斯酸比二酮和酮酯反应中使用的更强。在Hf(OTf)4存在下，研究了在芳环上具有各种取代基的苄醇与作为二酮的二苯甲酰甲烷(2b)的反应。富电子的苄醇与2b反应，收率为86 - 96%，缺电子的醇以79 - 65%的收率得到所需产物。尽管1-(4 - 硝基苯基)乙醇含有强吸电子基团，但其反应仍以61%的收率得到相应产物。也可以直接使用烯丙醇对二酮2b进行烯丙基化反应。催化剂可通过水萃取回收，最多可重复使用五次。
