The cycloaddition reaction of diazomethane with diethyl 1,3-butadienylphosphonates containing electronegative substituents on the α-carbon atom gave diethyl (4-alkenyl-Δ1-pyrazolin-3-yl)phosphonates in high yields. Thermolysis and the base-catalyzed reaction of the pyrazolinylphosphonates produced functionalized 2,4-pentadienylphosphonates and pyrazoles, respectively, in good yields.
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Minami et al. (1985) studied this question.
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