In 40 mL of 1:1 methylene chloride/diethyl ether was dissolved 100 mg 8 (0.37 mmol) and 112 mg dimethyl fumarate (0.78 mmol). A few crystals of p-toluenesulphonic acid (TsOH) were added and the mixture refluxed for 4 h. The solvent was removed under reduced pressure and the residue dissolved in 5 mL of methanesulphonic acid. After stirring for 1 hour, water was added and the mixture extracted with chloroform. The organic phase was separated, dried over MgSO 4 , ...
