a 시약 및 조건 : ( i ) iodine ( 1 . 0 equiv . ) , pyridine , 3 h at 140 ℃, 66 % yield ; ( ii ) aq . NaOH , EtOH , 1 - 3 h at room temperature , 28 . 8 - 81 . 7 % yield ; ( iii ) NH 4 OAc ( 10 . 0 equiv . ) , glacial acetic acid , 24 h at 100 ℃, 35 . 7 - 51 . 6 % yield .