[Cl:1][C:2]1[CH:11]=[C:10]2[C:5]([CH:6]=[CH:7][C:8](/[CH:12]=[CH:13]/[C:14]3[CH:15]=[C:16]([C:20](=[O:22])[CH3:21])[CH:17]=[CH:18][CH:19]=3)=[N:9]2)=[CH:4][CH:3]=1.C1(C)C=CC=CC=1.CS(O)(=O)=O.C1C(=O)N([Br:42])C(=O)C1>C(#N)C>[Br:42][CH2:21][C:20]([C:16]1[CH:17]=[CH:18][CH:19]=[C:14](/[CH:13]=[CH:12]/[C:8]2[CH:7]=[CH:6][C:5]3[C:10](=[CH:11][C:2]([Cl:1])=[CH:3][CH:4]=3)[N:9]=2)[CH:15]=1)=[O:22]To a warm (90° C.) and stirred solution of ketone 57 (5 g, 0.016 mol) in a mixture of 4:1 toluene and acetonitrile (125 ml) was added methane sulfonic acid (2.64 ml, 0.041 mole) and stirred for 1 hour. The reaction mixture was cooled to 68° C., NBS (3.19 g, 0.018 mol) was added at once and stirred the contents at 65° C. for 4 hour followed by stirring at RT for 18 hour. The solid from the reaction mixture was collected by filtration and dissolved in dichloromethane (100 ml). dichloromethane layer was washed with 10% aq. sodium carbonate and subjected to usual workup and concentration to obtain alpha bromo-ketone 58 (3.0 g, 48%) as an off-white solid.
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