An efficient asymmetric synthesis of (S)‐2,3‐dihydrobenzo[b]furan‐3‐carboxylic acid (8 a) and (S)‐5‐chloro‐2,3‐dihydrobenzo[b]furan‐3‐carboxylic acid (8 b) was established. Key to the success was the highly stereoselective enzymatic kinetic resolution of the corresponding methyl or ethyl esters that was further developed into a dynamic process. As a reliable and fast tool for analysing the enantiomeric excess, HPLC coupled with a CD detector was utilized. The route was completed by a Friedel–Crafts acylation of ethyl (S)‐5‐chloro‐2,3‐dihydrobenzo[b]furan‐3‐carboxylate (7 c) followed by saponification leading to (S)‐5‐chloro‐2,3‐dihydrobenzo[b]furan‐3‐carboxylic acid (2), an analgesic agent.

中文翻译：

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2,3-二氢苯并[b]呋喃的动力学动力学拆分：化学酶法合成止痛剂BRL 37959

（的有效不对称合成小号）-2,3-二氢苯并[ b ]呋喃-3-羧酸（8）和（小号）-5-氯-2,3-二氢苯并[ b ]呋喃-3-羧酸（8 b）成立。成功的关键是相应的甲酯或乙酯的高度立体选择性酶促动力学拆分，该拆分进一步发展成为一个动态过程。作为分析对映体过量的可靠且快速的工具，使用了带有CD检测器的HPLC。该路线是通过（S）-5-氯-2-3,2-二氢苯并[ b ]呋喃-3-羧酸乙酯的Friedel-Crafts酰化反应完成的（7 c），然后进行皂化，得到镇痛剂（S）-5-氯-2-3,3-二氢苯并[ b ]呋喃-3-羧酸（2）。