Trifluoroacetylation of electron-rich thiophenes

•Trifluoroacetylation of electron-rich thiophenes under mild conditions.•TFAA (1.2 equiv.) and pyridine (1.1 equiv.) are the reagents of choice.•Thiophenes with strong electron-donating groups give very good yields.•Thiophenes with weak electron-donating groups give low yields.

Electron-rich thiophenes were trifluoroacetylated by trifluoroacetic anhydride with different nitrogen bases in dichloromethane at room temperature in good yields. Trifluoroacetylation without a base gave significantly lower yields.

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