[C:1]12([C:13](=[O:14])[NH:12][C:11](=[O:15])[NH:10]1)[C:9]1[C:4](=[CH:5][CH:6]=[CH:7][CH:8]=1)[CH2:3][CH2:2]2.C[Si](N([Si](C)(C)C)C(=O)C(F)(F)F)(C)C.[Br:31]Br>C(Cl)(Cl)Cl>[Br:31][CH:3]1[C:4]2[C:9](=[CH:8][CH:7]=[CH:6][CH:5]=2)[C:1]2([C:13](=[O:14])[NH:12][C:11](=[O:15])[NH:10]2)[CH2:2]1Spiro[imidazolidine-4,1'-indan]2,5-dione, (C.A. reg. no. 6252-98-8) (6.06 g, 30 mmol) was combined with 7.95 ml (30 mmol) bis(trimethylsilyl)trifluoroacetamide and 4.8 g (30 mmol) bromine in 50 ml chloroform and heated to reflux. Decolorization occurred during the 18 hour reaction. The reaction mixture was cooled to 25° C. and after 45 minutes stirring a solid which had crystallized was collected by filtration to give 2.45 g (29%) of crude 3'-bromo-spiro[imidazolidine-4,1'-indan]2,5-dione. The chloroform mother liquors deposited an additional 2.18 g (26% yield), mp 58°-65° C. Two grams (7.1 mmol) of material, mp 58°-65° C., was combined with 25 ml water to give a slurry. Following stirring for 22 hours the resultant solid was collected by filtration and dried to give 0.52 g (33% yield) of the title compound: mp 260°-263° C.
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