General procedure for the synthesis of 4
To a reaction tube equipped with a stir bar were addedN -(quinolin-8-yl)benzamide (1a , 50 mg, 0.2 mmol),
2-diazo-1H -indene-1,3(2H )-dione (2 , 52 mg, 0.3
mmol), Co(acac)2 (10 mg, 0.04 mmol),
Ag2CO3 (165 mg, 0.6 mmol) and
CH3CN (1.5 mL). The tube was then sealed, and the
mixture was stirred at 100 °C (metal module heating) under
O2 for 24 h. Upon completion, it was cooled to room
temperature, filtered through a pad of celite, and concentrated under
reduced pressure. The residue was purified by silica gel column
chromatography using petroleum ether/ethyl acetate (3:1) as eluent to
afford 4a . Other products 4a-4s were obtained in a
similar manner.