Formation of Isolable Dearomatized [4 + 2] Cycloadducts from Benzenes, Naphthalenes, and <i>N</i>-Heterocycles Using 1,2-Dihydro-1,2,4,5-tetrazine-3,6-diones as Arenophiles under Visible Light Irradiation
Kazuki Ikeda, Riku Kojima, Kentaro Kawai, Takayasu Murakami, Takashi Kikuchi, M. Kojima, Tatsuhiko Yoshino, Shigeki Matsunaga
Abstract
We report that the dearomative [4 + 2] cycloaddition between 1,2-dihydro-1,2,4,5-tetrazine-3,6-diones (TETRADs) and benzenes, naphthalenes, or N -heteroaromatic compounds under visible light irradiation affords the corresponding isolable cycloadducts. Several synthetic transformations including transition-metal-catalyzed allylic substitution reactions using the isolated cycloadducts at room temperature or above were demonstrated. Computational studies revealed that the retro-cycloaddition of the benzene–TETRAD adduct proceeds via an asynchronous concerted mechanism, while that of the benzene–MTAD adduct (MTAD = 4-methyl-1,2,4-triazoline-3,5-dione) proceeds via a synchronous mechanism.