Recyclable Polymeric π-Acid Catalyst Effective in Aqueous and Solvent-Free Inverse-Electron-Demand Aza-Diels-Alder Reactions - Masaki, Yukio; Yamada, Tomoyasu; Kawai, Hyouei; Itoh, Akichika; Arai, Yoshitsugu; Furukawa, Hiroshi (Synlett, 2006)