purification. An equimolar
mixture of 3a and 4ab in 1,2-dichloroethane was treated with
1 equiv of chlorofumaryl chloride7 at ambient temperature
to provide a statistical mixture of bisonium chlorofumarate
and mixed onium chlorofumarate diesters 5-7. Title compounds
5ab were the major products isolated in 15% yield
by preparative HPLC as an inseparable 1:1 mixture of
chlorofumarate regioisomers.8