The synthesis of a permanent open form of a naphthopyran is described for the first time. The open form of the 10-hydroxy-2H-naphtho [1, 2-b] pyran, obtained by reaction of 1, 8- dihydroxy-naphthalene with 1, 1-diphenylprop-2-yn-1-ol under acid catalysis, is stable due to the establishment of an intramolecular hydrogen bond.
