1,1'-Biphenyl, 2-iodo- → 5-biphenyl-2-yl-5H-cyclopenta[2,1-b;3,4-b']dipyridin-5-ol

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Referring to scheme 6, under reflux, a flask containing with arylmagnesium iodide that was firstly prepared in advance from 2-iodo-biphenyl (11.2 g, 40 mmol) and magnesium (0.97 g, 40 mmol) in ether was added into 4,5-diazafluoren-9-one (3.64 g, 20 mmol) in THF. The mixture was refluxed for another 12 hours, then quenched with water after cooling to ambient temperature and extracted with CHCl3. The combined organic extracts were dried (MgSO4) and concentrated by rotary evaporation. The resulting crude solid was washed with n-hexane to give 5-biphenyl-2-yl-5H-cyclopenta[2,1-b;3,4-b′]dipyridin-5-ol (6.3 g, 93% yield) as a light brown solid, which was used for cyclization without further purification. 5-biphenyl-2-yl-5H-cyclopenta[2,1-b;3,4-b′]dipyridin-5-ol was heated to dissolve in 500 ml acetic acid. The solution was added 6 ml sulfuric acid as catalyst and refluxed for 24 hours. The reaction was quenched with cold water after cooling to room temperature and neutralized with NaOH(aq) to basic, then extracted with CHCl3 and dried with MgSO4. The combined organic solution was concentrated by rotary evaporation and washed with n-hexane to give 4,5-diaza-9,9′-spirobifluorene (4.3 g, 75%) as a light brown solid.

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