Hetero-diels–alder reaction of 5-ylidene-4-sulfanylidene-1,3-thiazolidin-2-ones with N,N′-bis(methoxycarbonyl)-1,4-benzoquinone diimine

Hetero-Diels–Alder reaction of 5-(propan-2-ylidene)-4-sulfanylidene-1,3-thiazolidin-2-one with N , N ′-bis(methoxycarbonyl)-1,4-benzoquinone diimine in boiling toluene afforded 87% of dimethyl 9,9-dimethyl-2-oxo-8a,9-dihydro-2 H -thiochromeno[2,3- d ][1,3]thiazole-5,8(3 H ,4a H )-diylidenedicarbamate. Analogous reactions of 5-benzylidene-, 5-{[4-(dimethylamino)phenyl]methylidene}-, and 5-[(2-hydroxyphenyl)-methylidene]-4-sulfanylidene-1,3-thiazolidin-2-ones led to the formation of the corresponding dimethyl 9-aryl-2-oxo-3,9-dihydro-2 H -thiochromeno[2,3- d ][1,3]thiazole-5,8-diyldicarbamates in 64–82% yield.