The Diels-Alder cycloadditions of the alpha-acetoxynitroso dienophile in water are reported. The rapid and high yielding synthesis of structurally diverse 3,6-dihydro-1,2-oxazines complements the straightforward elaboration of aminoalcohols obtained from the alpha-acetoxynitroso derivative in anhydrous medium. A rationale for this solvent-dependent product distribution is proposed.