Radical cation Diels–Alder reactions of arylidene cycloalkanes

• Kaii Nakayama,
• Hidehiro Kamiya and
• Yohei Okada

Beilstein J. Org. Chem. 2022, 18, 1100–1106, doi:10.3762/bjoc.18.112

• to be much more effective in the reaction than other cycloalkanes. Since the reaction is completed with a substoichiometric amount of electricity, a radical cation chain pathway is likely to be involved. Keywords: arylidene cycloalkane; Diels–Alder reaction; radical cation; single-electron transfer

• there is some correlation between these arylidene cycloalkane cycloadditions. Control studies are summarized in Table 1. LiClO4, TiO2, and light were crucial for the reaction (Table 1, entries 1–4) and the equivalents of the diene 2 was also key (entries 5 and 6 in Table 1). The reaction was sensitive

• appropriate arylidene cycloalkane (0.20 mmol), 2,3-dimethyl-1,3-butadiene (2, 113 μL, 1.0 mmol), and TiO2 (100 mg) were added to a solution of LiClO4/CH3NO2 (1.0 M, 4.0 mL) while stirring at room temperature. The resulting reaction mixture was stirred at room temperature in front of a 15 W UV lamp (365 nm