Iron-Catalyzed Oxidative Radical Alkoxycarbonylation of Activated Alkenes with Carbazates toward Alkoxycarbonylated Benzimidazo[2,1-a]isoquinolin-6(5H)-ones

Abstract

A FeCl₂·4H₂O-catalyzed oxidative alkoxycarbonylation of activated alkenes with carbazates toward alkoxycarbonylated benzimidazo[2,1-a]isoquinolin-6(5H)-ones has been established. The reaction proceeded smoothly to furnish a series of structurally diverse benzimidazo[2,1-a]isoquinolin-6(5H)-one frameworks in moderate to good yield.

Key words

iron catalysis - carbazates - hydrazinecarboxylates - alkoxycarbonylation - benzimidazoisoquinolinones - alkenes

Publication History

Received: 26 March 2021

Accepted after revision: 29 March 2021

Accepted Manuscript online:
29 March 2021

Article published online:
10 May 2021

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• 13 Methyl (5-Methyl-6-oxo-5,6-dihydrobenzimidazo[2,1-a]isoquinolin-5-yl)acetate (3a): Typical Procedure 70% aq TBHP (1.0 mmol) was added to a mixture of 1-methacryloyl-2-phenyl-1H-benzimidazole (1; 0.25 mmol), methyl carbazate (1.25 mmol), and FeCl₂·4 H₂O (0.05 mmol) in MeNO₂ (2 mL), and the mixture was heated at 80 °C for 6 h. The solvent was removed under reduced pressure, and the residue was purified by column chromatography [silica gel, PE–EtOAc (4:1 to 6:1)] to give a white solid; yield: 40 mg (50%); mp 207–208 °C.¹H NMR (400 MHz, CDCl₃): δ = 8.51 (dd, J = 7.7, 1.6 Hz, 1 H), 8.39–8.34 (m, 1 H), 7.87–7.81 (m, 1 H), 7.57–7.35 (m, 5 H), 3.71 (d, J = 17.2 Hz, 1 H), 3.37 (s, 3 H), 3.21 (d, J = 17.2 Hz, 1 H), 1.64 (s, 3 H). ¹³C NMR (100 MHz, CDCl₃): δ = 172.8, 170.5, 149.8, 144.0, 141.7, 131.8, 131.5, 127.9, 126.3, 125.8, 125.5, 125.0, 122.9, 119.8, 116.6, 51.9, 46.5, 44.1, 30.1. HRMS (ESI): m/z [M + H]⁺ calcd for C₁₉H₁₇N₂O₃: 321.1239; found: 321.1235.