Kinetic Resolution Displaying Zeroth Order Dependence on Substrate Consumption: Copper-Catalyzed Asymmetric Alcoholysis of Azlactones
journal contributionposted on 05.04.2006, 00:00 by Makoto Tokunaga, Junya Kiyosu, Yasushi Obora, Yasushi Tsuji
Kinetic resolution of 4-alkyl-2-aryl-5-oxo-4,5-dihydrooxazole-4-carboxylic acid esters (azlactones 1) were achieved by copper-DTBM-SEGPHOS catalyzed alcoholysis reaction with good selectivity (12 examples). Variation of ee of unreacted substrates 1 and products 2 with conversion was found to follow the theoretical line of zeroth-order kinetic resolution, for which the selectivity profiles and graphical analysis were presented for the first time. The efficiency of resolution in zeroth-order reaction is higher than first-order reaction. For example, the reaction with 1a afforded (S)-1a (99% ee) and (R)-2a (74% ee) at 57% conversion, where the krel values were calculated to be 6.7 as zeroth-order kinetic resolution and 37 as first-order kinetic resolution.