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Mechanism of a No-Metal-Added Heterocycloisomerization of Alkynylcyclopropylhydrazones: Synthesis of Cycloheptane-Fused Aminopyrroles Facilitated by Copper Salts at Trace Loadings

Congratulations to the Hein lab, who’s recent publication in the Journal of the American Chemical Society was just selected for a Spotlight review. This collaborative study brought together leaders in both synthetic (Richmond Sarpong) and computational (Dean Tantillo) to perform a detailed investigation on the mechanism of a “metal-free” heterocycloisomerization that forms annulated aminopyrroles. Through kinetic isotope effect studies and unexpected rate differences among starting materials with different purification methods, the authors identify a copper complex present in trace amounts as the active catalyst for this transformation. This discovery is enabled by combined experimental and computational evaluations of model systems as well as extensive analytical instrumentation. The reported work is an important contribution to the field of organic synthesis and provides a mechanistic model for systematically determining whether a no-metal-added catalytic system is truly metal-free.

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