✍ Scribed by Jiming Xiang; Baolin Li
No coin nor oath required. For personal study only.
A concise and enantioselective synthesis of (S)‐ethyl 2‐cyclopentyl‐2‐hydroxy‐2‐arylacetate, a key intermediate for the muscarinic receptor, is reported. The tertiary stereogenic center was constructed with good stereoselectivity through the __L‐__proline‐catalyzed direct asymmetric aldol reaction of ethyl arylglyoxylate and cyclopentanone. The carbonyl of the condensation product was reduced using a modified Clemmensen reaction which provided an easier workup and was more environmentally acceptable. The enantioselectivity of the aldol reactions was between 58.3%–93.2%, which means that the stereoselective is efficient in controlling configuration of reaction product.
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## Abstract The CoCl~2~/L‐proline (1:2) system was found to be an excellent catalyst for direct aldol reactions. Excellent yields (up to 93 %) and a significant improvement in diastereoselectivity (__anti__/__syn__ up to 45:1) as well as enantioselectivity (up to more than 99 % __ee__) compared wit