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The ethyl 2-amino-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate (8.0 g, 0.0355 mol) and ethyl-2-cyanoacetate (8.03 g, 0.0710 mol) was dissolved in dioxane (250 ml). It was cooled to 0° C. To this reaction mixture, HCl gas was purged up to saturation (for 20 min, initially reaction mass becomes turbid and then becomes clears). Then reaction mass was stirred for 18 h at room temperature. After completion of the reaction it was cooled to 0° C. and basified with saturated NaHCO3 (pH=8). Further it was extracted with ethyl acetate (250 ml×3). Combined organic extracts were washed with water followed with brine. Separated organic layer was dried over anhy. Na2SO4, filtered and concentrated to get 9 g crude product. It was purified by column chromatography by using 100-200 mesh silica gel and 1-2% MeOH: DCM solvent system to give ethyl 2-(4-hydroxy-5,6,7,8-tetrahydrobenzo[4,5]thieno[2,3-d]pyrimidin-2-yl)acetate as yellow solid. Yield—(9.0 g, 86.71%); 1H-NMR: (400 MHz, CDCl3); δ=4.25-4.20 (q, 2H), 3.77 (s, 2H), 3.00-2.97 (m, 2H), 2.76-2.74 (m, 2H), 1.88-1.81 (m, 4H), 1.29-1.25 (t, 3H); LC-MS [M+H]=292.9.

1. customTo this reaction mixture, HCl gas was purged up to saturation (for 20 min
2. custominitially reaction mass
3. customThen reaction mass
4. customAfter completion of the reaction it
5. extractionFurther it was extracted with ethyl acetate (250 ml×3)
6. washCombined organic extracts were washed with water
7. customSeparated organic layer was dried over anhy
8. filtrationNa2SO4, filtered
9. concentrationconcentrated
10. customto get 9 g crude product
11. customIt was purified by column chromatography