Yield:23688-07-5 91%

Reaction Conditions:

with diisopropylamine in tetrahydrofuran;cyclohexane;N,N-dimethyl-formamide;

Steps:

28.A Step A

Step A 3,5-Dibromo-2-thiophenecarboxaldehyde To a solution of 2,5-dibromothiophene (20.0 g, 82.7 mmol) in anhydrous THF (200 mL) at -70° C. was added a 1.5M solution of LDA in cyclohexane (60.6 mL, 90.9 mmol) over 10 min. The mixture was stirred for 1 h before anhydrous DMF (18.1 g, 248 mmol) was added. The resulting mixture was stirred overnight, solvent evaporated, the residual oil poured into 2N HCl (200mL), and this mixture was extracted with ethyl acetate (2*200 mL). The combined extracts were dried (MgSO₄) and evaporated to give a brown solid (20.21 g, 91%) which was used in the next step without further purification.

References:

US5538966,1996,A