@article{gupta_kumar_paul_2010,  title={Silica functionalized sulfonic acid catalyzed one-pot synthesis of 4,5,8a-triarylhex-ahydropyrimido[4,5-d]pyrimidine-2,7(1H,3 H)-diones under liquid phase catalysis},  volume={21},  ISSN={0103-5053},  url={https://doi.org/10.1590/S0103-50532010000200022},  DOI={10.1590/S0103-50532010000200022},  number={2},  journal={Journal of the Brazilian Chemical Society},  publisher={Sociedade Brasileira de Química},  author={Gupta, Princy and Kumar, Vineet and Paul, Satya},  year={2010},  pages={349–354} }