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Part-IExperimental4.5 Oxidation of condensed 2-(1H-benzimidazole-2-yl)methylthiopyrimidin-4(3H)-ones using meta-chloro perbenzoic acid (m-CPBA) to obtain correspondingsulfinyl derivatives (IVi-xxxv)1. Synthesis of 2-(1H-benzimidazol-2-yl)methylsulfinyl-5,6,7,8-tetrahydro-benzo-(b)sulfinyl[2,3-d]pyrimidin-4-(3H)-one using m-CPBA (IVi)2-(1H-Benzimidazol-2-yl)methylthio-5,6,7,8-tetrahydrobenzo(b)thieno[2,3-d]pyrimidin-(3H)-one (IIIi, 1.98 gm; 0.0054 mole) was dissolved in 125 ml methanol and 100 mlmethylene dichloride by stirring at room temprature. The reaction mixture was chilled inan ice salt bath while maintaining the temperature below 0 o C. To this clear solution,methanolic solution of m-CPBA (1.16 gm; 0.0065 mole) was added with stirring andcontinued the stirring for 30-45 mins. Progress of the reaction was monitored usingprecoated TLC using benzene: methanol::4.5:0.5 as a solvent system. After completion ofthe reaction, the reaction was stopped by the addition of 10% sodium bicarbonate. Theorganic layer was separated and washed with 10% NaCl and water (50 ml each). Theorganic layer was dried with anhydrous sodium sulphate and solvent was distilled outunder reduced pressure to obtain the crude product and on recrystallization frommethanol-chloroform, afforded crystalline material (0.78 gm; 74% yield), m.p. 216-218 o C.Mol. Formula : C 18 H 16 N 4 O 2 S 2 ; Mol. Wt. 384IR (KBr) cm -1 : 3235(γ NH ), 2946(γ C-H ), 1655(γ CONH ), 1060(γ S-O ), 747(γ C-S )NMR (DMSO-d 6 )δppm : 1.79-1.83 (4H, m, CH 2 at 6 & 7), 2.54-2.79 (4H, m, CH 2 at 5 &8), 5.58 (2H, s, CH 2 at SCH 2 ), 7.39-7.16 (4H, m, Ar-H), 12.60(1H, s, NH), 13.80 (1H, s, NH).MS(m/e) : 368, 364, 335, 218.2. Synthesis of 2-{[(5-methoxy-1H-benzimidazol-2-yl) sulfinyl]methyl}-5,6,7,8-tetrahydro[1]benzo-thieno[2,3-d]pyrimidin-4(3H)-one(IVii)2-{[(5-Methoxy-1H-benzimidazol-2-yl)thio]methyl}-5,6,7,8-tetrahydro[1]benzothieno-[2,3-d]pyrimidin-4(3H)-one (IIIii, 2.14 gm; 0.0054 mole) was dissolved in 125 mlmethanol and 100 ml methylene dichloride by stirring at room temprature. Thereafter, thereaction mixture was chilled in an ice salt bath while maintaining the temperature below0 o C. To this clear solution, methanolic solution of m-CPBA (1.16 gm; 0.0065 mole) was203