Studies on heterocyclic compounds. VII. Syntheses of novel furo[2,3-b]chromones [1]
Furo[2,3-b]chromone (1a) was conveniently prepared by the PPE-promoted cyclization of 5-[2'-carboxy-phenoxy)furan-2-carboxylic acid (8) which was made from methyl salicylate and ethyl 5-nitrofuran-2-carboxylate. Furo[2,3-b]chromon-2-acrylic acid (13) was