Benzo[c][1,2]thiazine-Based Analogs in the Inverse Electron Demand [4+2] Hetero Diels-Alder Reaction with Glycals: Access to Tetracyclic Fused Galactose and Fucose Derivatives

The synthesis and reactivity in an [4+2] inverse electron demand hetero Diels-Alder reaction (ihDA) of an original class of electron-poor heterodienes, the N-substituted-1H-benzo[c][1,2]thiazin-4-one-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.