Hexabromotricyclobutabenzene and hexabromohexaradialene: Their nickel-mediated one-pot syntheses and crystal structures

Article abstract of DOI:10.1002/chem.19970030207

The reaction of hexakis(dibromomethyl)benzene with [(Bu₃P)₂Ni(COD)] (COD - 1,5-cyclooctadiene) in DMF at 65 70 C yielded a mixture of the title compounds. The mixture was separated by column chromatography to yield hexabromotricyclobutabenzene (3a) and hexabromohexaradialene (4) in 24 and 16% yields, respectively. ¹H and ¹³C NMR spectroscopy suggest that 3 is obtained as the syn-all-trans isomer 3a, and the symmetric anti-all-trans isomer 3b is not obtained at all. The X-ray structures of 3a and 4 are reported. The hexaradialene 4 has a chair conformation, and deviates from planarity by 43.6. Heat or radical impurities cause the clean transformation of 3a to 4.