Diastereoselective Synthesis of (Z)-6-(2-Oxo-1,2-dihydro-3H-indol-3-ylidene)-3,3a,9,9a-tetrahydroimidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazin-2,7(1H,6H)-diones

Two efficient and diastereoselective procedures for the synthesis of (Z)-6-(2-oxo-1,2-dihydro-3H-indol-3-ylidene)-3,3a,9,9a-tetrahydroimidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazin-2,7(1H,6H)-diones by aldol-crotonic condensation of 1,3-dimethyl-3a,9a-diphenyl-3,3a,9,9a-tetrahydroimidazo[4,5-e]thiazolo[3,2-b]-1,2,4-triazin-2,7(1H,6H)-dione with isatins under acidic or basic catalysis are reported. Isomerization in (Z)-7-(1-allyl-2-oxo-1,2-dihydro-3H-indol-3-ylidene)-1,3-dimethyl-3a,9a-diphenyl-1,3a,4,9a-tetrahydroimidazo[4,5-e]thiazolo[2,3-c]-1,2,4-triazin-2,8(3H,7H)-dione was observed under basic conditions.