Porphyrins are 1 8π aromatic macrocycles having four pyrrole units linked via methine bridges and exhibit interesting optical and electrochemical properties. A few transition metal-catalyzed cross-coupling reactions such as the Sonogashira and Suzuki-Miyaura reactions, have been successfully applied to the synthesis of porphyrins, but the use of organometallic reactions is still not common. Recently, our group has reported that the reaction of meso-bromoporphyrins with alkynes under palladium catalysis afforded fused porphyrin derivatives as a consequence of [3 + 2] annulation at β and meso positions. On the other hand, Arnold et al. reported that the reaction of meso-bromoporphyrins with alkenes such as methyl acrylate, styrene, and acrylonitrile, resulted in normal Mizoroki-Heck reactions only at the meso position. Herein we report that the reaction of meso-bromoporphyrins with various strained alkenes such as norbornadiene under palladium catalysis leads to [3 + 2] annulation at β and meso positions to provide novel porphyrin derivatives in high yields with perfect exo-selectivity.
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