Iron-Catalyzed Cross-Dehydrogenative Coupling of para-Quinone Methides with Formamides: In Situ Activation of C(sp2)-H Bonds

A novel and straightforward method for the iron-catalyzed regioselective cross-dehydrogenative coupling of para-quinone methides (p-QMs) with formamides has been developed, facilitated by the in situ activation of the C(sp²)-H bonds of the formyl and alkenyl substituents via a radical strategy. This method does not require the preactivation of the substrates, and it can accommodate a wide range of p-QMs and formamides under the optimized reaction conditions, resulting in the formation of the expected C-7 acetamides-functionalized para-quinone methides with moderate to good yields. The control experiments revealed that the reaction follows the fundamental equation of second-order kinetics. Additionally, an exploration of the Hammett effect was undertaken to elucidate the impact of the substituents for the reaction. In combination with the DFT calculation, a plausible reaction mechanism was proposed through meticulously controlled experiments.