This study demonstrates the design, synthesis, and first application of novel aminooxylating reagents that serve as a useful d0a3 synthon equivalents for organic synthesis. It has been demonstrated that their reaction with α,β-unsaturated aldehydes performed under aminocatalytic conditions provides a straightforward access to polysubstituted tetrahydro-1,2-oxazine derivatives, direct precursors of functionalized 1,4-amino alcohols. Target tetrahydro-1,2-oxazine derivatives have been obtained with high yields (up to 89%) and with excellent stereocontrol (up to >20:1 dr, > 99.5:0.5 er). Furthermore, the synthetic usefulness of tetrahydro-1,2-oxazines obtained has been demonstrated in various selective transformations.