Cascade in Situ Iodination, Chromone Annulation, and Cyanation for Site-Selective Synthesis of 2-Cyanochromones.

A facile cascade reaction for the site selective synthesis of 2-cyanochromones is described. By using simple o -hydroxyphenyl enaminones and potassium ferrocyanide trihydrate (K 4 [Fe(CN) 6 ] 3 ·3H 2 O) as starting materials and I 2 /AlCl 3 as promoters, the products are furnished via tandem chromone ring formation and C-H cyanation. The in situ formation of 3-iodochromone and a formal 1,2-hydrogen atom transfer (HAT) process account for the unconventional site selectivity. In addition, the synthesis of 2-cyanoquinolin-4-one has been realized by employing corresponding 2-aminophenyl enaminone as substrate.