Carbazole Based Smaragdyrins: Synthesis, Aromaticity Switching, and Formation of a Spiro-Dimer.

Carbazole-incorporated smaragdyrin BF 2 -complex 3 was synthesized by S N Ar reaction of 3,5-dibromo-8-mesityl-BODIPY 1 with 3,6-di(tert-butyl)-1,8-di(pyrrol-2-yl)carbazole 2 as a nucleophile. Demetalation of 3 with ZrCl 4 gave the corresponding smaragdyrin free base 4 in a good yield. Oxidations of 3 and 4 with MnO 2 gave smaragdyrins 5 and 6, respectively, both followed by aromaticity switching, since the oxidized products showed a moderate paratropic ring current owing to their 20π-electronic circuits. Further, treatment of 4 with [RhCl(CO) 2 ] 2 in the presence of NaOAc gave Rh I complex 7, and oxidation of 3 with RuCl 3 in the presence of triethylamine led to the formation of a spiro dimer product, 8.