Cyclobutadiene is a highly reactive antiaromatic hydrocarbon that has fascinated chemists for over 60 years. However, its preparation and uses in chemical synthesis are sparing, in part due to its lengthy synthesis that generates hazardous byproducts including excess heavy metals. Herein, we report a scalable, metal-free cyclobutadiene reagent, diethyldiazabicyclohexene dicarboxylate, and explore its intermolecular [4 + 2] cycloaddition with various electron-deficient alkenes. We also demonstrate its utility in a three-step synthesis of dipiperamide G and a diverse array of product derivatizations including bromocyclobutadiene.

This study presents a scalable, metal-free cyclobutadiene reagent, diethyldiazabicyclohexene dicarboxylate, for intermolecular [4 + 2] cycloadditions and its utility in the synthesis of dipiper

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A Metal-Free Cyclobutadiene Reagent for Intermolecular [4 + 2] Cycloadditions.

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