A Rapid Intramolecular Imino Diels-Alder Reaction of Aminoanthraquinones with Citronellal or Prenylated Salicylaldehydes: Substituent Effect on Changing the Reaction Pathway from Diels-Alder to Ene-Type Cyclization - Gaddam, Vikram; Meesala, Ramu; Nagarajan, Rajagopal (Synthesis, 2007)