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

                  Dissolved 8.012 g of I in 100 mL of THF and 25 mL of water.  Stirred at 0 C.  Added 9.6 mL of 30% aq. H₂O₂ followed by 1.392 g of LiOH-H₂O.  After 1 h, TLC (30:70 EtOAc-hexanes, UV) showed the disappearance of the starting material spot at Rf 0.74.  The reaction mixture was quenched with a solution of 12.012 g of Na₂SO₃ in 75 mL of water.  The biphasic mixture was concentrated by rotary evaporation and extracted with CH₂Cl₂ to remove the oxazolidinone.  The pH of the aqueous layer was lowered to ~1 with 1.0 M HCl and 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 30:70 EtOAc-hexanes as eluant.  The product was a clear, colorless oil. 

 

¹H NMR (CDCl₃, 300 MHz) d 2.84 (m, CHCO₂, 1H), 2.58 (dd, J = 16.5, 9.3 Hz, CH₂CO₂t-Bu, 1H), 2.36 (dd, J = 16.5, 4.9 Hz, CH₂CO₂t-Bu, 1H), 1.59 (m, CH₂, 2H), 1.42 (s, C(CH₃)₃, 9H), 1.30 (m, CH(CH₃)₂, 1H), 0.93 (d, J = 6.6 Hz, CH(CH₃)₂, 3H), 0.89 (d, J = 6.0 Hz, CH(CH₃)₂, 3H).

 

notes

 

Lithium hydroperoxide has been found to be the reagent of choice for regioselective hydrolysis of N-acyl carboxamides (see Evans, D.A.; Britton, T.C.; Ellman, J.C.  Tetrahedron Lett.  1987, 28, 6141).  Hydrolysis of these N-acyl oxazolidinones can proceed by two possible pathways.  Amide hydrolysis (path a) affords the desired carboxylic acid and recovered chiral auxilliary.  However, as the size of R increases, carbamate hydrolysis (path b) occurs to a greater and greater extent.  This problem is largely overcome by the use of LiOOH formed in situ by the addition of LiOH (pKa 11.6) to H₂O₂ (pKa 15.8).