Stereospecific preparation of (2E, 4Z)-monofluorodienyl esters by the Heck reaction of high E/Z ratio 1-bromo-1-fluorostyrenes

High E/Z ratio (E/Z>75:25) 1-bromo-1-fluorostyrenes, which were prepared by isomerization of 1-bromo-1-fluorostyrenes (E/Z≈1:1), underwent the Heck reaction with methyl acrylate, and (2E, 4Z)-methyl 5-aryl-4-fluoropenta-2,4-dienoates were successfully isolated. Heck reactions of (Z)-1-bromo-1-fluorostyrenes also occur. However, the products are difficult to separate in a pure form, since they have an obvious tendency to isomerize on a silica gel column.