1-O-tert-butyl 2-O-methyl (2S)-2,3-dihydropyrrole-1,2-dicarboxylate

Conditions: temp:85.01; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a solution of 27.3 g of the compound obtained in Step 19-1 in toluene (500 ml) was added 1,8-diaza bicyclo[5,4,0]undec-7-ene (DBU) (12.7 ml) and the reaction mixture was stirred for 10 hours at an external temperature of 85° C. After being to cool, the precipitation was separated by filtration and the solvent was evaporated under reduced pressure. The obtained residue was separated and purified by column chromatography (silicagel 60; mobile phase: EtOAc/n-hexane=1/10 to 1/5; v/v) to obtain 4.15 g of 1-tert-butyl 2-methyl (2S)-2,3-dihydro-1H-pyrrole-1,2-dicarboxylate (colorless oil) and 12.5 g of 1-tert-butyl 2-methyl (2S)-2,5-dihydro-1H-pyrrole-1,2-dicarboxylate (colorless oil). to cool the precipitation was separated by filtration the solvent was evaporated under reduced pressure The obtained residue was separated purified by column chromatography (silicagel 60; mobile phase: EtOAc/n-hexane=1/10 to 1/5; v/v)