Electrochemical Allene C─H Functionalization via Carbanion Sampling

Abstract

Abstract Functionalization of C─H bonds represents a direct and practical avenue to upgrade simple organic molecules to value‐added products, whereas the reaction selectivity is largely governed by the acidity and bond dissociation energy (BDE) of C─H bonds. Developing a novel strategy to break these constraints is highly desirable, as it would open a new horizon for conventionally challenging molecules. Herein, we disclosed a carbanion sampling strategy that enables unconventional selectivity in the allene C(sp 2 )─H functionalization harnessing chromium‐catalyzed hydrogen evolution. The electrochemical protocol provides in situ access to diverse allene carbanions and facilitates a dynamic carbanion sampling process to give thermodynamically unfavored products. 1,3‐Disubstituted allenes were precisely functionalized at the less acidic and stronger C(sp 2 )─H site to yield abnormal site‐selective allene products, while the 1,1‐substituted allenes proceeded isomerization to deliver functionalized alkynes. All of the products presented in this work are unprecedented and exhibit remarkable versatility in late‐stage derivatization. The superiority of the carbanion sampling strategy was demonstrated in the convergent synthesis of functionalized allenes from alkyne or mixed substrates. More importantly, we conducted a series of density functional theory (DFT) calculations and control experiments to rationalize the unconventional selectivity.