a-Hydroxynaphthylthiophthalimide (1) is a suitable precursor of the reactive ortho-thioquinone 2, which can be generated in situ and trapped by glycals. The reaction is an inverse electron-demand [42] cycloaddition that occurs in a totally regioselective and highly stereoselective way. A series of differently substituted glycals (3, 5 ± 12, 21, 22, 38) as well as various ortho-thioquinones (25 ± 27) are successfully used as electron-rich dienophiles and electron-poor dienes, respectively, with chloroform, dimethylformamide, and dimethyl sulfoxide as solvents. The stereochemistry of substituents on the dienophile strongly influences the selectivity of the cycloaddition, which becomes totally stereoselective when galactals 8 ± 10 or arabinals 21 and 22 are employed as dienophiles. Among the heterodienes tested, the a-naphthol derivative 25 and the tyrosine derivative 26 were successfully used to prepare the naphthyl-a-O-rhamnoside 32 a and the tyrosine-a-O-glucoside 34, respectively. Cycloadducts 4 a, 17, 24, and 33 a were successfully desulfurized, affording the corresponding aryl 2-deoxy-a-O-glycosides 39 and 40 ± 42.