Abstract Dry reaction of indoles and alkylindoles (1a–h) with triethyl orthoformate (2.5 equiv.) on acid??washed montmorillonite K10 clay at room temperature afforded in< 5 min–4 hr the respective symmetrical TIMs (2a–h) in good to high yields along with the formylindole 3 and the formyl??TIM 4 from 1g and 1h, respectively.