The same 1 : 1 crystalline complex, mp 110-1 11 ', was obtained by crystallizing solutions of equivalent amounts of 2 and 6 from hexane.Octabromofulvalene (8). In 25 ml of 1,Z-dimethoxyethane was dissolved 10.8 g (0.020 mol) of 2. Water (2 ml) was added, and the mixture was cooled to -80" with stirring, then 5.75 g (0.040 mol) of copper(1) bromide was introduced. The mixture was allowed to warm slowly. Near 0" the water melted and the mixture turned dark green. The CuBr dissolved in 3-5 min at Oo, and a purple precipitate formed. The mixture was immediately filtered, and the purple solid was purified by chromatography on silicic acid in a 1 :1 hexane-chloroform solution, yield 0.50 g (6.6%) of 8 as dark blue crystals, mp 170" dec.Anal. Calcd for CloBrs: C, 15.8; H, 0.00; C1, 0.00; Br, 84.2. Found: C, 15.95; H,0.00; C1,0.00; Br, 82.9.The infrared spectrum of 8 is given in Table I1 and Figure 1. The electronic spectrum is shown in Figure 2; vmax, cm-l (log e): 45,240(4.32); 24,150(4.67); and 15,690(2.37).Abstract: Dimethyl acetylenedicarboxylate was treated with 1-trimethylsilylcyclopentadiene t o yield a mixture of 7-trimethylsilyl-and 5-trimethylsilyl-2,3-bis(methylcarboxylato)bicyclo[2.2.l]heptadienes. Thermal isomerization of the 7-trimethylsilyl derivative to the 5-trimethylsilyl isomer was shown not to occur. Reactions between ( C H & 5 i k C R , where R is H, COCH1, or C02C2H5, and l-trimethylsilylcyclopentadiene were carried out at 1 80-260°, and only vinyl-substituted derivatives were obtained. I t is suggested that l-trimethylsilylcyclopentadiene undergoes temperature-dependent tautomerism, which may be viewed as a 1,3-proton shift, to form 3-
