The Vilsmeier–Haack formylation of 2,3-dihydro-4H-1,3-benzoxazin-4-ones and isomeric 1,2-dihydro-4H-3,1-benzoxazin-4-ones: an effective approach to functionalized 2H-/4H-chromenes and tetrahydroacridines

Abstract We found that 1,3- and isomeric 3,1-benzoxazin-4-ones react with the Vilsmeier reagent in vastly different ways. Thus, either 2 H - or 4 H -chromenes were obtained in good yields when 1,3-benzoxazin-4-ones were reacted at 75–80 °C, while the formylation of 3,1-benzoxazines at ambient temperature leads to acridine-9-one or 9-chloroacridine derivatives, depending on the amount of Vilsmeier reagent and the nature of substrate.