Tracking the Process of Solvothermal Domino Reaction Leading to a Stable Triheteroarylmethyl Radical: A Combined Crystallography and Mass Spectrometry Study

A new‐type of carbon free radical 1 was obtained from a microwave assisted solvothermal reaction of a primary amine (L1) with FeCl3·6H2O in methanol at 140 ºC. Through a combination of crystallography and electrospray ionization mass spectrometry (ESI‐MS), the reaction process was studied. The possible mechanism consists of coordination, oxidative self‐condensation, cyclization, and aromatization to give a "dimer" (3). Sequential activation of methanol, confirmed by 13CH3OH and CD3OD labeling experiments, is followed by the coupling with two and three molecules of (3) to give a "tetramer" (2) and a "hexamer" (1), respectively. For the first time, the homolytic cleavage of C‐O bond is applied to synthesize triarylmethyl radical. This is so far the longest domino reaction, including 14 steps and forming up to 12 new covalent bonds (9 C‐N and 3 C‐C) and 3 five‐membered heterocycles. Furthermore, considering the many reaction steps, the yield of 1 (30%) is relatively high, showing the high average transformation efficiency of each step. The atom economy of this reaction is 91.8%. This reaction is potentially useful in the synthesis of stable radicals.

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