3,4-Dihydroxy-2,3,5-trimethyl-6-oxo-cyclohexa-1,4-dienecarboxylic acid ethyl ester 、 在
四丁基氟化铵 作用下,
以
四氢呋喃 为溶剂,
生成 (4S,4aS,9aR)-4,4a-Dihydroxy-6-methoxy-3,4,5,8,9a-pentamethyl-1-oxo-4,4a,9,9a-tetrahydro-1H-xanthene-2,7-dicarboxylic acid diethyl ester 、 (4R,4aS,9aS)-4,4a-Dihydroxy-6-methoxy-3,4,5,8,9a-pentamethyl-1-oxo-4,4a,9,9a-tetrahydro-1H-xanthene-2,7-dicarboxylic acid diethyl ester