Evans Aldol Reaction: Experimental
Procedure/experimental
To a solution of 6 (10.43 g, 38.16 mmol) in CH2Cl2 (400 ml) was added TiCl4 (4.39 ml,40.1 mmol) dropwise at -78 °C. After stirring for 5 minutes, N,N-diisopropylethylamine (16.5 mL,95.5 mmol) was added to the resultant yellow solution at -78 °C. The dark purple solution of a titanium enolate was stirred for 1 hours at -78 °C. To a solution of the titanium enolate was added N-methlpyrrolidone (3.66 ml, 38.2 mmol). After stirred for 15 minutes, to this solution was added 19 (14.43 g, 38.16 mmol) portionwise at -78 °C. The resulting mixture was stirred for 1 hour at -78 °C and warmed to 0 °C. After stirred for 1 hour at same temperature, the reaction mixture was poured into sat. NH4Cl, and the resulting mixture was extracted with CH2Cl2 three times. The combined organic extracts were washed with sat. NaHCO3 and brine, dried over MgSO4, filtrated,and evaporated under reduced pressure. The residue was purified by column chromatography on silica gel (20% AcOEt in hexane) to afford 20 (20.26 g, 81.50%) as a yellow solid.
