In memory of Prof. Giovanni Romeo, who gave a fundamental contribution to the field of cycloaddition reactionsThe synthesis and reactivity in an [4 + 2] inverse electron demand hetero Diels-Alder reaction (ihDA) of an original class of electronpoor heterodienes, the N-substituted-1H-benzo [c][1,2]thiazin-4one-2,2-dioxides, are described. These are highly reactive electrophiles that allow easy access to unprecedented benzo-thiazine glyco-fused derivatives in a remarkably selective way, even when using acetylated glycals, previously unexplored within this version of ihDA. DFT calculations support the experimental data, and moreover show that acetylated dienophiles can easily react making cycloadditions feasible.