1, 3-Dipolar Cycloadditions. LXXVI. Cycloadditions of Diazomethane to Substituted Butadienes

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.