5-Chloro-2-thiophenecarboxylic acid → 5-chloro-N-(prop-2-yn-1-yl)thiophene-2-carboxamide

Participants

Reaction Steps

2-Fluoro-4-iodoaniline (1.1, 6.50 g, 27.4 mmol) was dissolved in 25 mL TFA and stirred in ice bath. Solid NaNO2 (2.07 g, 30.1 mmol) was added in small portions. The resulting mixture was stirred for 30 min in ice bath. Sodium azide (1.87 g, 28.8 mmol) was dissolved in 10 mL water and chilled in ice bath. This cold solution was then added to the TFA solution in three portions. The mixture was stirred in ice bath for 1 hr and concentrated in vacuo to remove TFA. The residue was taken into 600 mL DCM and washed with water three times. The organic phase was dried using MgSO4 and concentrated in vacuo to afford 1-azido-2-fluoro-4-iodobenzene 1.2 as a brownish waxy solid in >99% yield. In the mean time, 5-chlorothiophene-2-carboxylic acid (1.3, 9.13 g, 56 mmol) was dissolved in 200 mL dry DCM along with 0.5 mL dry DMF. To the vigorously stirred solution was carefully added oxalyl chlororide (14.7 mL, 169 mmol) dropwise. The resulting solution was stirred for 3 hrs at RT and concentrated in vacuo. The residue was pumped to dryness and then dissolved in 300 mL dry DCM. To this solution was added propargylamine (5.8 mL, 84 mmol) dropwise. The mixture was stirred at RT overnight during which time solid precipitated out. 600 mL hexane was added and the mixture was vigorously stirred for a few hours. The solid was collected by filtration and washed with hexane to give 5-chloro-N-(prop-2-ynyl)thiophene-2-carboxamide 1.4 (9.47 g, 85%) which was used directly without further purification. MS found for C8H6ClNOS as (M+H)+ 200.0, 202.0 (chlorine pattern).

Provenance & Evidence