Skeletal rearrangement of arylmethylideneimidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazine-2,7-diones in the synthesis of the corresponding imidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazine-2,8-diones

(Z)-1,3-Dialkyl-7-arylmethylidene-1,3a,4,9a-tetrahydroimidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazine-2,8(3H,7H)-diones have been prepared via a chemo- and diastereoselective aldol condensation of 1,3-dialkyl-3,3a,9,9a-tetrahydroimidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazine-2,7(1H,6H)-diones with aromatic aldehydes followed by the skeletal rearrangement of thiazolotriazine fragments. We succeeded in synthesizing hitherto unknown products of alkali-induced skeletal rearrangement of 3a,9a-diphenyl substituted imidazothiazolotriazines.