The unique reactivity of 5,6-unsubstituted 1,4-dihydropyridine in the Huisgen 1,4-diploar cycloaddition and formal [2 + 2] cycloaddition

• Xiu-Yu Chen,
• Hui Zheng,
• Ying Han,
• Jing Sun and
• Chao-Guo Yan

Beilstein J. Org. Chem. 2023, 19, 982–990, doi:10.3762/bjoc.19.73

• ; isoquinolino[1,2-f][1,6]naphthyridine; Introduction Among various well-known cycloaddition reactions such as the 1,3-dipolar cycloaddition reaction, Diels–Alder reaction, and the Povarov reaction, the cycloaddition reaction of Huisgen 1,4-dipoles with activated alkenes received increasing attention [1][2][3

• reaction was carried out in common solvents such as ethanol, methanol, dichloromethane, and chloroform at room temperature for two hours. The expected isoquinolino[1,2-f][1,6]naphthyridine derivative 4a was successfully obtained in 35%, 40% 70% and 65% yields, respectively (Table 1, entries 1–4). The

• for developing the scope of the reaction and the results are summarized in Table 2. It can be seen that all reactions gave the desired isoquinolino[1,2-f][1,6]naphthyridine derivatives 4a–o in good to excellent yields. Isoquinoline itself and its 4-, 5-, and 6-bromo-substituted derivatives were