Isolation of theZ-isomer The Z-isomer 38 may be isolated from the reaction mixture by crystallization. However the overall yield increases significantly by the addition of ether, concen- trated HCI and ZnCI2 in quantities just enough to create a homogeneous solution. Pure 38 begins to crystallize after some time and almost all of the isomer 7 is con- verted into 38. Presumably the high initial concentration of the thermodynamically less stable isomer 38 leads to its ...
