1,8-Diazabicyclo(5.4.0)undec-7-ene → Ethyl thieno[2,3-b]thiophene-2-carboxylate

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Reaction Steps

To a solution of 2-(carboethoxymethylthio)3-formylthiophene (from step c) in MeOH (200 mL) was added DBU (0.6 mL, 4.0 mmole) at 0° C. After 1 hr the mixture was warmed to RT and concentrated. The residue was taken up in EtOAc, washed with 10% HCl, H2O (3×), dried (MgSO4), and concentrated. Flash chromatography on silica gel (50% toluene/hexanes) gave the title compound (3.84 g, 45% over 4 steps) as an off-white solid: 1H NMR (400 MHz, CDCl3) δ 7.95 (s, 1 H), 7.40 (d, J=5.2 Hz, 1 H), 7.26 (d, J=5.2 Hz, 1 H), methyl ester 3.92 (s, 3 H), ethyl ester 4.38 (q, J=7.1 Hz, 2 H)) and 1.41 (t, J=2.4 Hz, 3 H).

Provenance & Evidence