Synthesis of substituted benzo[b][1,4]oxazepine derivatives by the reaction of 2-aminophenols with alkynones

We have developed a novel synthetic method accessing benzo[b][1,4]oxazepines that are one of the rare classes of benzoxazepine derivatives by reaction of 2-aminophenols with alkynones in 1,4-dioxane at 100 °C. A series of benzo[b][1,4]oxazepine derivatives can be prepared by using this synthetic protocol. Mechanistic experiments indicated that the hydroxy proton of the aminophenol could play a crucial role in the formation of an alkynylketimine intermediate that undergoes 7-endo-dig cyclization.