[NH:1]1[C:6](=[O:7])[CH2:5][S:4][C:3]2[CH:8]=[CH:9][C:10]3[C:15]([C:2]1=2)=[CH:14][CH:13]=[CH:12][CH:11]=3.[Cl:16][C:17]1[CH:24]=[CH:23][C:20]([CH:21]=O)=[CH:19][CH:18]=1.C[O-].[Na+].CN(C)C=O>O>[Cl:16][C:17]1[CH:24]=[CH:23][C:20]([CH:21]=[C:5]2[S:4][C:3]3[CH:8]=[CH:9][C:10]4[C:15]([C:2]=3[NH:1][C:6]2=[O:7])=[CH:14][CH:13]=[CH:12][CH:11]=4)=[CH:19][CH:18]=1A mixture of 1H-naphtho[2,1-b][1,4]thiazin-2(3H)-one (5.17 g), 4-chlorobenzaldehyde (5.62 g), sodium methoxide (1.73 g) and dimethylformamide (80 ml) is refluxed for 4.5 hours. After cooling, the reaction mixture is poured into water and the resulting precipitate is separated by filtration, washed and dried and then is recrystallized from tetrahydrofuran-n-hexane to give 3-(4-chlorobenzylidene)-1H-naphtho[2,1-b][1,4]thiazin-2(3H)-one (4.28 g). M.p. 277°-279° C.
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