At a loading as low as 0.5 mol% indium triflate has been found to catalyse the hetero Diels-Alder reaction. A three component coupling reaction between aldehydes, amines and Danishefsky's diene to afford tetrahydropyridine derivatives proceeds similarly in high yield.
Ali, T., Chauhan, K. K., & Frost, C. G. (1999). Indium triflate an efficient catalyst for hetero Diels-Alder reactions. Tetrahedron Letters, 40(30), 5621-5624. https://doi.org/10.1016/S0040-4039(99)01045-X