An unexpected ring-opening of a 2-pyrone ring at low temperatures. A mild and expeditious synthesis of novel coumarins

When the iminium salts of ortho-hydroxy arylaldehydes were condensed with a 4-hydroxy-2-pyrone at room temperature or well below, a series of unique coumarins were isolated via a translactonization at the expense of an unexpected ring-opening of the 2-pyrone nucleus.