Pindur, Ulf, and Myung-Hwa Kim. “Nevv Reactions of Vinylindoles As Heterocyclic Dienes With 4-Phenyl-1,2,4-Triazoline-3,5-Dione: Non-Concerted Versus Concerted Processes”. CHIMIA, vol. 44, no. 10, Oct. 1990, p. 339, doi:10.2533/chimia.1990.339.