[S:1]1[C:5]2[CH2:6][N:7]([C:10]([O:12][C:13]([CH3:16])([CH3:15])[CH3:14])=[O:11])[CH2:8][CH2:9][C:4]=2[CH:3]=[CH:2]1.C([Li])CCC.[CH2:22]([O:24][C:25](Cl)=[O:26])[CH3:23]>C1COCC1>[S:1]1[C:5]2[CH2:6][N:7]([C:10]([O:12][C:13]([CH3:16])([CH3:15])[CH3:14])=[O:11])[CH2:8][CH2:9][C:4]=2[CH:3]=[C:2]1[C:25]([O:24][CH2:22][CH3:23])=[O:26]A solution of tert-butyl 4,7-dihydrothieno[2,3-c]pyridine-6(5H)-carboxylate in dry THF was cooled to −78°, n-butyl lithium (1.5 eq.) was added slowly and reaction mixture stirred for 3-4 hrs. This reaction mixture was then added to the solution of ethylchloroformate (10 eq.) in dry THF at −78° C. Reaction mass wan then allowed to come at room temperature and stirred overnight. It was then cooled and quenched with ammonium chloride solution and extracted with ethyl acetate, dried over sodium sulphate and concentrated. The crude was then purified using column chromatography to yield 6-tert-butyl 2-ethyl 4,7-dihydrothieno[2,3-c]pyridine-2,6(5H)-dicarboxylate.
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