Procedure:  250 mL 1-neck flask, stirbar, septum, N₂ inlet

                  Dissolved 9.996 g of I in 120 mL of dry THF.  Stirred; cooled to -78 C.  Added 22.5 mL of 2.5 M n-BuLi in hexanes.  The mixture turned yellow.  Added 7.80 mL of II and warmed the reaction mixture to 0 C.  After 1 h, TLC (30:70 EtOAc-hexanes, UV) showed product spot at Rf 0.64.    The reaction was then quenched with sat. aq. K₂CO₃ and stirred for 1 h.  The mixture was then extracted with EtOAc.  The organic layer was dried over MgSO₄, filtered and the solvent was removed by rotary evaporation.  The product was isolated by flash chromatography on silica gel using 10:90 EtOAc-hexanes as a clear, colorless oil. 

 

¹H NMR (CDCl₃, 300 MHz) d 7.36-7.20 (m, ArH, 5H), 4.67 (m, oxazolidinone CH, 1H), 4.18 (m, ArCH₂, 2H), 3.30 (dd, J = 13.2, 3.3 Hz, H1, 1H), 2.94 (m, oxazolidinone CH₂, 2H), 2.76 (dd, J = 13.2, 9.9 Hz, H1, 1H), 1.59 (m, H2, H3, 3H), 0.94 (d, J = 6.0 Hz, CH(CH₃)₂, 6H). 

 

notes

 

The use of (S)-4-benzyl-2-oxazolidinone as chiral auxiliary will direct the addition to afford alpha-(R) alkylated addition product (see Part 2).  Opposite product stereochemistry can be obtained using the enantiomeric oxazolidinone.  Other  chiral auxiliaries that have been used include 4-isopropyl-2-oxazolidinone, 4-methyl-5-phenyl-2-oxazolidinone (see Evans, D.A.; Ennis, M.D.; Mathre, D.J.  J. Am. Chem. Soc.  1982, 104, 1737) and (cis)-3,3a,8,8a-tetrahydro-2H-indeno[1,2-d]-oxazol-2-one (see Ghosh, A.K.; Liu, W.  J. Org. Chem.  1996, 61, 6175).