Racemate of (3aS,4S,9bS)-4-(p-tolyl)-2,3,3a,9b-tetrahydro-4H-furo[3,2-c]chromene

Trans diastereomer was obtained by employing MeSO3H (50 mol%) in toluene [0.2 M] with equimolar amounts of p-Me homoallylic alcohol and salicylaldehyde and allowing to the reaction to run for 5 hrs at room temperature (d.r= 5:1) with no stirring. N.B. This system was found to not be homogenous and so unsuitable for NMR analysis. The reaction was then quenched by addition of aq. NaHCO3 and diastereomers were separated by preparative TLC (20% diethyl ether in petroleum ether).

反式非对映异构体（Trans diastereomer）可通过如下方法得到：以等物质的量的对甲基高烯丙醇（p-Me homoallylic alcohol）与水杨醛（salicylaldehyde）为底物，使用50 mol%的甲磺酸（MeSO3H）作为催化剂，在浓度为0.2 M的甲苯（toluene）溶剂中，于室温、无搅拌条件下反应5小时，反应的非对映选择性比例（d.r., diastereomeric ratio）为5:1。注（N.B.）：该反应体系为非均相体系，因此不适用于核磁共振（NMR, nuclear magnetic resonance）分析。随后向反应体系中加入碳酸氢钠水溶液（aq. NaHCO3）淬灭反应，再通过制备薄层色谱（preparative TLC，展开剂为含20%二乙基醚的石油醚）分离得到各非对映异构体。