[3+2] Cycloaddition reactions of diethyl (E)-2-fluoromaleate

Diethyl E-2-fluoromaleate has been prepared in a pure state in 89% yield by a Horner–Wadsworth–Emmons Wittig procedure. The E configuration was determined by NMR spectroscopy. Diethyl E-2-fluoromaleate undergoes [3+2] cycloadditions with a series of aromatic α-iminoesters and aromatic nitrones. The yields of purified cyclic products ranged from 65 to 80%.