A new method for synthesis of 4, 5-dihydro-1, 4-oxazepines is reported.Using readily available 1-sulfonyl-1, 2, 3-triazoles and α, β-unsaturated aldehydes as starting materials, 1, 4-oxazepines were synthesized conveniently in moderate yields in the presence of Rh2(Oct)4.Moreover, this transformation manifests the potential utility of 1-sulfonyl-1, 2, 3-triazole as precursor of aza-1, 3-dipole in formal 4+3 cyclization.