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

Double S_NAr reaction of 3,5-dibromo-8-mesityl-BODIPY 1 with 3,6-di(tert-butyl)-1,8-di(pyrrol-2-yl)carbazole 2 gave carbazole-incorporated smaragdyrin BF₂-complex 3, which was converted to free base 4, Rh^I complex 7, and spiro dimer 8, through different reaction pathways. Oxidation of nonaromatic smaragdyrins 3 and 4 with MnO₂ gave moderate antiaromatic smaragdyrins 5 and 6, respectively.

Abstract

Carbazole-incorporated smaragdyrin BF₂-complex 3 was synthesized by S_NAr 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 ZrCl₄ gave the corresponding smaragdyrin free base 4 in a good yield. Oxidations of 3 and 4 with MnO₂ 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 RuCl₃ in the presence of triethylamine led to the formation of a spiro dimer product, 8.

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