2-Cyclopenten-1-one → 2-Tert-butylcyclopentadiene

Participants

Reaction Conditions

Reaction Steps

2-Cyclopenten-1-one (14.2 mL, 0.17 mol) was added dropwise over about 30 min. at about -78° C. to t-BuLi (340 mmol) in dry THF (450 mL). The reaction was allowed to warm to about 20° C. and then chilled to about -78° C. to quench with NH4Cl (18.2 g). Solvent was removed in vacuo and the residue was partitioned between Et2O (300 mL) and brine (100 mL). The organic phase was washed with brine, dried over MgSO4 (s), filtered and concentrated in vacuo. The residue of crude 1-tert-butylcyclopent-2-en-1-ol (23.8 g) was treated with benzenesulfonic acid (0.24 g) in refluxing Et2O for 1.5 h. Solvent was removed in vacuo and the residue was vacuum distilled (12 mm, ~27-30° C.) to obtain pure 2-tert-butylcyclopentadiene (4.2 g). This diene (1.3 g, 10.7 mmol) was dissolved in xylene (5 mL) along with a crystal of hydroquinone and trans-β-nitrostyrene (1.95 g, 13.1 mmol). The tube was sealed under N2 (g) and heated to about 140° C. for about 10 h. Flash chromatography on silica (30% CH2Cl2 /hexanes) afforded 1.79 g (GC-MS m/z 271) of the nitro derivative which was reduced by dropwise addition of an etheral (10 mL) solution over 20 min. to LiAlH4 (0.5 g) in Et2O (25 mL). The mixture was refluxed for about 5 h. and quenched by serial additions of H2O (0.5 mL), 15% NaOH (0.5 mL) and H2O (1.5 mL), respectively. The mixture was filtered and the filtrate was washed with saturated aqueous NaHCO3 and brine, dried over MgSO4 (s), filtered, and concentrated in vacuo. The residue (1.1 g) was dissolved in dry Et2O (6 mL), chilled to about 5° C., and treated dropwise with 1M HCl in Et2O (6 mL) to precipitate the desired amine as its HCl salt (610 mg; LC-MS m/z 242).

Provenance & Evidence