Amidation reaction of carboxylic acid with formamide derivative using SO₃•pyridine

The amidation reaction of carboxylic acid derivatives was developed using sulfur trioxide pyridine complex (SO₃•py) as a commercially available and easily handled oxidant. This method could be applied to the reaction of various aromatic and aliphatic carboxylic acids, including optically active ones, with formamide derivatives to afford the corresponding amides in good to high yields.