A dry 50 mL Schlenk flask with magnetic stirring bar was charged with 854 mg ( 3.36 mmol , 1.0 eq ) 4-(benzyloxy)isobenzofuran-1,3 - dione ( 11 )   The spectra are in accordance with previously reported data . [ 8 ] ( S)-9- ( Benzyloxy)-1,2,3,11a- The solvent was removed in vacuum and the resulting solid was dried in oil pump vacuum . [ 8 ] Yield :   The spectra are in accordance with previously reported data . [ 8 ] Benzyl ( S)-9-(benzyloxy)-5,11 - dioxo-2,3,11,11a - tetrahydro-1H - benzo saturated NH 4 Cl solution were added and the mixture was stirred for 5 min . The mixture was diluted with CH 2 Cl 2 ( 50 mL ) and the solid was removed via filtration through a sintered glass frit and was rinsed with CH 2 Cl 2 . The combined organic phases were dried over Na 2 SO 4 , filtrated and the solvent was removed in vacuum . The product was purified via column chromatography ( 60 g silica gel , size : 20 x 3 cm , cyclohexane / CH 2 Cl 2 /acetone = 10:10:1