Dimethyl Sulfate → 2,4-Dibromo-3,5-dimethylthiophene

Participants

Reaction Steps

A solution of 2,4,5-tribromo-3-methylthiophene (50.2 g, 0.15 mol; Gronowitz, S.; Moses, P. Hakansson Arkiv. f. Kemi. 1960, 14, 267) in 400 mL of diethyl ether was cooled to -78° C., and a solution of nBuLi (100 mL, 1.6M) was added dropwise. The starting material precipitated out of solution, but when n-BuLi added, the reaction mixture became stirrable again. When the addition was complete, the reaction mixture was stirred for 20 min, and then a solution of dimethyl sulfate (75.7 g, 0.600 mol) in 200 mL of diethyl ether which was cooled to -50° C. was added by cannulation. When addition was complete, the reaction mixture was allowed to warm to ambient temperature and was stirred overnight. The reaction was quenched with 100 mL of 6N NaOH solution and stirred for 2h. The mixture was transferred to a separatory funnel, and the aqueous layer was separated and extracted with additional ether. The organic layers were combined, washed with water and brine and dried (MgSO4). The suspension was filtered and concentrated to give an oil. Vacuum distillation provided 22.1 g (55%) of 2,4-dibromo-3,5-dimethylthiophene, A8, b.p. 71°-72° C. @ 0.4 mmHg. The 1H NMR in CDCl3 supported the assigned structure. ##STR58##

Provenance & Evidence