1,10-Phenanthroline-5,6-dione

Typical Procedure: (Scheme1, R¹ = H): A 25 mL flask is charged with 1,10-phenanthroline-5,6-dione (10.5 mg, 0.05 mmol) and 1,2,3,4-tetrahydro-6,7-dimethoxyisoquinoline (194.6 mg, 1.0 mmol) and anhydrous CH₃CN (3.0 mL) is added. The flask is flushed with O₂ and equipped with an O₂ balloon. A well-dissolved solution of ZnI₂ (7.98 mg, 0.025 mmol) and PPTS (37.7 mg, 0.15 mmol) in anhydrous CH₃CN (1.0 mL) is then added. The reaction is stirred vigorously at room temperature for 24 h. The mixture is diluted in EtOAc (50 mL) and washed with 1M NaOH (25 mL). The aqueous phase is extracted with additional EtOAc (2 x 25 mL). The combined organic phases are washed with brine (25 mL), dried over Na₂SO₄, and concentrated. The residue is purified by column chromatography on silica gel (eluent: EtOAc/hexanes or EtOAc) to give 3,4-dihydro-6,7-dimethoxyisoquinoline (176.1 mg, 91% yield) as a viscous oil.

1,10-Phenanthroline-5,6-dione (0.618 g, 2.94 mmol) and 2,3-diamino-1,4-naphthoquinone hydrochloride (0.660 g, 2.94 mmol) are suspended in dry ethanol (40 mL). The mixture is refluxed for 1.5 h under a N₂ atmosphere. A green solid is formed. The mixture is cooled to rt and the solid is filtered, washed with ethanol and diethyl ether. After drying under high vacuum, the desired lignad 1 (0.926 g, 87%) are obtained as a green powder.