Phenylacetylene → 6,7-Dichloro-2,3-dimethoxy-5-(2-phenylethynyl)quinoxaline

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Reaction Steps

A mixture of 6,7-dichloro-2,3-dimethoxy-5-iodoquinoxaline (Preparation 108, 5.0 g, 13 mmol), phenylacetylene (3.98 g, 39 mmol), bis(triphenylphosphine)palladium(II) chloride (0.913 g, 1.3 mmol) and copper(I) iodide (0.248 g, 1.3 mmol) in triethylamine (100 mL) was heated under reflux for 4 hours. After being cooled, the mixture was concentrated under reduced pressure and the residue partitioned between dichloromethane (200 mL) and brine (200 mL). The phases were separated and the aqueous phase extracted with dichloromethane (2×100 mL). The combined organic extracts were dried (MgSO4) and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel, by gradient elution using hexane:dichloromethane (1:0 changing to 1:1, by volume) to afford 6,7-dichloro-2,3-dimethoxy-5-(2-phenylethynyl)quinoxaline (3.60 g, 77%) as a yellow solid, mp 170-172° C.

Provenance & Evidence