Preparation of diazocyclopentadiene
0.5 mole of phenyllithium prepared from 14 g. of lithium metal and 78 g. of bromobenzene is filtered by forcing through a tube containing glass wool by means of pressure from a tank of pre-purified nitrogen. The obtained phenyllithium solution is cooled and of a solution of 33 g. of freshly distilled cyclopentadiene in 150 ml. of dry ether was added dropwise with stirring over a period of 30 min. After being stirred another hour at room temperature, the suspension of cyclopentadienyllithium is forced under nitrogen pressure in a slow, steady stream into a cooled, stirred solution of 100 g. of p-toluenesulfonyl azide in 300 ml. of dry ether. The reaction became deep yellow almost immediately and gradually turned reddish-brown. A precipitate appeared during the addition which required one hours. Rapid filtration separated the mixture into a solid phase and a red ether solution which was extracted several times twice with 100-ml. portions of water, dried over anhydrous sodium sulfate and concentrated. Distillation of the residue through a short Vigreux column yields 16 g. (35% of theory) of red diazocyclopentadiene, b.p. 52-53°C at 50 mm. Diazocyclopentadiene is purified by crystallization first from alcohol and then from pentane, both at -70°C. The heavy yellow needles melted at -23 to -22°C to a red liquid, n25/D=1.6150 (at 25°C), d29/25=1.059.
W. von E. Doering and C. H. DePuy, J. Am. Chem. Soc., 75, 5955 (1953).
5-Diazo-1,3-cyclopentadiene, 1,3-Cyclopentadiene,5-diazo-, 1192-27-4, Diazocyclopentadiene, Cyclopentadiene, 5-diazo-, 5-diazocyclopenta-1,3-diene, AC1L39L8, 1,3-Cyclopentadiene, 5-diazo-, UETCMNDFHMOYSP-UHFFFAOYSA-N, OR109720