[Cl:1][C:2]1[CH:15]=[CH:14][C:13]2[O:12][C:11]3[C:6](=[CH:7][C:8]([C:16](=[N:18][OH:19])[CH3:17])=[CH:9][CH:10]=3)[S:5][C:4]=2[CH:3]=1.B.N1C=CC=CC=1.Cl>C(O)C.C1COCC1>[Cl:1][C:2]1[CH:15]=[CH:14][C:13]2[O:12][C:11]3[C:6](=[CH:7][C:8]([CH:16]([NH:18][OH:19])[CH3:17])=[CH:9][CH:10]=3)[S:5][C:4]=2[CH:3]=1
To a suspension of 2-chloro-8-(1-hydroximinoethyl)phenoxathiin (C.A. 66, 2519a, 1967) (425 mg, 1.456 mmol) in ethanol (12 mL) and THF (5 mL) at room temperature there was added pyridine-borane (271 mg, 0.3 mL, 2.92 mmol) and 4M ethanolic HCl (1.1 mL, 4.4 mmole); the mixture was stirred at room temperature overnight, there was added more pyridine-borane (0.35 mL) and 4M ethanolic HCl (2 mL) and stirring was continued for 2 hours. The solvents were evaporated, the residue diluted with water and ethyl acetate and basified with 1N aqueous NaOH. From the organic phase a crude product was obtained which was chromatographed on silica gel, eluting with a 1:1 mixture of ethyl acetate-hexane, to afford the title product (344 mg) as a white solid, m.p.: 103°-105° C.
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