A new and efficient method for the synthesis of hitherto unreported spiro[benzo[4,5]thiazolo[3,2-a] chromeno[2,3-d]pyrimidine-14,3'-indoline]-1,2',13(2H)-triones was developed via the Domino Knoevenagel condensation-Michael addition-intermolecular cyclization sequences of isatin derivatives, cyclohexane-1,3-diones, and 2-hydroxy-4H-benzo14,51thiazolo[3,2-a]pyrimidin-4-ones, employing 12-tungstophosphoric acid (H3PW12O40) as an effective and inexpensive catalyst. (C) 2018 Elsevier Ltd. All rights reserved.