Stereoselectivity in 1,3-Dipolar Cycloaddition Reactions of 2-Benzopyrylium-4-olate with Acrylic Acid Derivatives Catalyzed by Rare Earth Metal Triflates - Inoue, Kei; Suga, Hiroyuki; Inoue, Shuichi; Sato, Hiroki; Kakehi, Akikazu (Synthesis, 2003)