Rhodium‐Catalyzed 1,4‐Addition of Lithium 2‐Furyltriolborates to Unsaturated Ketones and Esters for Enantioselective Synthesis of γ‐Oxo‐Carboxylic Acids By Oxidation of the Furyl Ring with Ozone |
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Authors: | Dr Xiao‐Qiang Yu Tomohiko Shirai Dr Yasunori Yamamoto Prof?Dr Norio Miyaura |
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Institution: | Division of Chemical Process Engineering, Graduate School of Engineering, Hokkaido University, N13, W8, Sapporo 060‐8628 (Japan), Fax: (+81)?11‐706‐6560 |
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Abstract: | Rhodium‐catalyzed 1,4‐addition of lithium 5‐methyl‐2‐furyltriolborate (ArB(OCH2)3CCH3]Li, Ar=5‐methyl‐2‐furyl) to unsaturated ketones to give β‐furyl ketones was followed by ozonolysis of the furyl ring for enantioselective synthesis of γ‐oxo‐carboxylic acids. Rh(nbd)2]BF4 (nbd=2,5‐norbornadiene) chelated with 2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl (binap) or 2,3‐bis(diphenylphosphino)butane (chiraphos) gave high yields and high selectivities in a range of 91–99 % ee at 30 °C in a basic dioxane/water solution. The corresponding reaction of unsaturated esters, such as methyl crotonate, had strong resistance under analogous conditions, but the 1,4‐adduct was obtained in 70 % yield and with 94 % ee when more electron‐deficient phenyl crotonate was used as the substrate. |
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Keywords: | 1 4‐addition asymmetric synthesis carboxylic acids ketones ozonolysis |
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