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A new strategy has been established for the synthesis of polysubstituted morpholin‐2‐ones through Stevens rearrangements of tertiary amines via in situ activation with epoxides. A range of α‐amino acid‐derived tertiary allylic, propargylic, and benzylic amines reacted with epoxides in the presence of zinc halide catalysts to afford structurally diverse allyl‐, allenyl‐, and benzyl‐substituted morpholin‐2‐ones, respectively, in moderate‐to‐good yields with high regioselectivity. The process involves [2,3]‐ and [1,2]‐Stevens rearrangements of quaternary ammonium ylide intermediates and constitutes a very convenient method to prepare polysubstituted morpholin‐2‐ones through tandem formation of C−N, C−O, and C−C bonds. Moreover, replacing epoxides with aziridines permitted the synthesis of polysubstituted piperazin‐2‐ones. New Stevens rearrangement: Zinc‐halide‐catalyzed ring‐opening of epoxides with α‐amino acid‐derived tertiary allylic, propargylic, and benzylic amines followed by [2,3]‐ and [1,2]‐Stevens rearrangements of the resulting quaternary ammonium ylide intermediates has been established as a convenient method to access polysubstituted morpholin‐2‐ones through tandem formation of C−N, C−O, and C−C bonds (see scheme). [ABSTRACT FROM AUTHOR]