A concise synthetic route to valuable highly functionalized benzosulfamidate-fused tetrahydroquinazoline is presented. The [4+2] cycloaddition of o-N-Cbz-amino-β-nitrostyrene with benzoxathiazine 2,2-dioxide using an imidazole as the catalyst afforded tetrahydroquinazolines with high diastereoselectivities. Furthermore, a chiral quinine-derived squaramide organocatalyst promoted an asymmetric [4+2] cycloaddition reaction, providing enantioenriched benzosulfamidate-fused tetrahydroquinazolines with good enantiopurities (up to 69:31 er).