Diels-Alder Reaction of Ni(II) β-Vinyl-meso-tetraphenylporphyrin; A General Method for Synthesis of Functionalized Porphyrins - Matsumoto, Kiyoshi; Kimura, Shinya; Morishita, Takuya; Misumi, Yukihiro; Hayashi, Naoto (Synlett, 2000)