[H-].[Na+].[CH3:3][CH:4]([C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])[C:5]([O:7][C:8]([CH3:11])([CH3:10])[CH3:9])=[O:6].[Br:19]Br>O1CCCC1.ClCCl>[Br:19][C:4]([CH3:3])([C:5]([O:7][C:8]([CH3:9])([CH3:10])[CH3:11])=[O:6])[C:12]([O:14][C:15]([CH3:17])([CH3:16])[CH3:18])=[O:13]To a stirred suspension of sodium hydride (1.7 g, 80% dispersion in oil) in tetrahydrofuran (60 ml) under an atmosphere of nitrogen was added di-t-butyl methylmalonate (11.52 g). The mixture was stiirred at 60°-70° for 1.5 hours to give a clear solution. This solution was cooled to -25°, and to it was rapidly added a solution of bromine (2.6 ml) in dichloromethane (30 ml). The solution was allowed to warm to ambient temperature, then concentrated. The residue in ether was washed with water, dried, and fractionally distilled under reduced pressure to give the title compound b.p. 78°-86°/1.0 mm Hg, (7.56 g, 49%); νmax (CHBr3) 1730cm-1 (CO2But); τ (CDCl3) values include 8.05 (s, C(CH3)3) and 8.53 (2s, CH3 and C(CH3)3).
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