Copper (I) Catalysed Conjugate Addition of Grignard Reagents to EnonesCopper (I) Catalysed Conjugate Addition of Grignard Reagents to Enones
SyntheticPage 35
Published Jul 18, 2001
Magnesium metal (0.61g, 25.0mmol) was activated by heating (heat gun) for 5 min with a crystal of I2 in dry THF (40cm3) under an Ar atmosphere. To this rapidly stirred suspension was added 4-bromobut-1-ene (2.54cm3, 25.0 mmol) dropwise via syringe. After the initial exotherm had subsided the reaction mixture was stirred for a further 1 h after which HMPA (9cm3) was added and the mixture cooled to -78°C. Anhydrous copper (I) iodide (0.39g, 2.05mmol) was added in one portion and the resulting slurry stirred for a further 10min. To this was added a mixture of 2-cyclohexenone (2.0g, 20.8mmol) and TMSCl (6.2cm3, 48.85 mmol) in 20cm3 dry THF dropwise over 10min. The resulting white suspension was stirred for 1h at -78°C, before the addition of Et3N (5cm3) and allowing to warm to RT. The resulting suspension was poured onto pet. ether (250cm3), washed with water (3 x 200cm3), dried over MgSO4 and the solvent evaporated to give a clear yellow oil. Kugelrohr distillation (130-140° @ 20mmHg) gave the pure product as a clear liquid (4.1g,88%).