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We present a divergent strategy that permits access to diversely functionalized benzoxazepinium scaffolds fused to various heterocycles. The described strategy features a one-pot combination of the Groebke–Blackburn–Bienaymé reaction and an aza-Michael addition. Methyl (E)-4-(2-formylphenoxy)but-2-enoate and its derivatives are utilized as central elements in this cascade. These building blocks are reacted with a variety of functionalized amino-azines and tert -butyl isocyanide under ytterbium triflate [Yb(OTf)3 ] catalysis. The ensuing cascade represents a rapid, modular and atom-economic process that leads to the construction of a diverse collection of constrained benzoxazepinium systems from a wide substrate scope. [ABSTRACT FROM AUTHOR]