Abstract
1-Substituted butadienes (R=CH2, CH3, O, C3H5, CO2CH3, CN) and 2-phenylbutadiene accept diazomethane at the 3, 4-bond yielding 3-vinylpyrazoline derivatives. Tautomerization of the 1-to 2-pyrazolines takes place either at room temperature (R=CO2CH3, CN), on heating (R=C6H5) or on acid catalysis (R=H, CH3, OCH3) ; the 2-pyrazolines are characterized as 1-carbamoyl and 1-nitroso derivatives. 1-Substituted butadienes follow in their rate constants of diazomethane cycloaddition a linear free energy relationship with Hammett's σp values, ρ=+4.2. The rates and orientations are discussed in the light of the recent MO perturbation treatment.
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