[CH3:1][O:2][CH2:3][N:4]1[C:9]2[CH:10]=[C:11]([C:14](OC)=[O:15])[CH:12]=[CH:13][C:8]=2[S:7][C:6]2[N:18]=[CH:19][CH:20]=[N:21][C:5]1=2.[H-].C([Al+]CC(C)C)C(C)C>C(Cl)Cl.C1(C)C=CC=CC=1>[CH3:1][O:2][CH2:3][N:4]1[C:9]2[CH:10]=[C:11]([CH2:14][OH:15])[CH:12]=[CH:13][C:8]=2[S:7][C:6]2[N:18]=[CH:19][CH:20]=[N:21][C:5]1=2Into a solution of 350 g of methyl 10-methoxymethyl-10H-pyrazino[2,3-b][1,4]benzothiazine-8-carboxylate in methylene chloride (2.5 l) was added dropwise under a nitrogen atmosphere 3.2 l of a 1.01 M solution of diisobutylaluminum hydride in toluene while maintaining the system at a temperature not exceeding 15° C. Then the reaction mixture was poured into ice and stirred for 1 hour. After filtering off the insoluble matter, the filtrate was washed with water. After distilling off the solvent under reduced pressure, the crude crystals thus obtained were washed with diisopropyl ether to thereby give 250 g of the title compound as pale yellow crystals.
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