Pyrazolines are an important class of organic compounds, because they possess a wide range of biological activities. Dialkyl azodicarboxylates and triphenylphosphine react to form the Huisgen zwitterion. The cycloaddition reactions of the zwitterion with alkynes and allenes leading to pyrazoles and pyrazolines have been studied. However, few reactions of the zwitterion and alkenes to afford pyrazolines have been reported. In this study, the reaction of an activated alkene with the zwitterion has been investigated. Treatment of 1,1-diethyl 2-t-butyl ethenetricarboxylate and diethyl azodicarboxylate with 1 equivalent of PPh3 in ether at room temperature for 18 h gave a pyrazoline product in 85% yield and quantitative triphenylphosphine oxide. The reaction of various ethenetricarboxylates and diethyl azodicarboxylate with PPh3 gave pyrazolines efficiently.  This pyrazoline synthesis is also applicable to 2-substituted acrylates such as trimethyl 2-phosphonoacrylate and methyl 2-(trifluoromethyl)acrylate.

Triphenlyphosphine-mediated reaction of dialkyl azodicarboxylate with activated alkenes leading to pyrazolines

244th National Meeting (2012)

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