Tandem Regioselective Substitution and Palladium‐Catalyzed Ring Fusion Reaction for Core‐Expanded Boron Dipyrromethenes with Red‐Shifted Absorption and Intense Fluorescence

Abstract

A selective method for the core-extension of boron dipyrromethene (BODIPY) with two annulated indole rings with exclusive syn-connectivity is reported. The method is based on a regioselective nucleophilic substitution reaction of 2,3,5,6-tetrabromoBODIPY with aryl amines, followed by palladium-catalyzed intramolecular C-C coupling ring fusion. The unsymmetrical core-expanded BODIPY with annulated indole and benzofuran rings was also synthesized by stepwise and regioselective nucleophilic substitution and palladium-catalyzed intramolecular C-C coupling reaction. The diindole-annulated BODIPY was unambiguously characterized by single-crystal X-ray analysis. The optical properties of the present core-expanded BODIPYs were studied, revealing clearly red-shifted absorption and emission bands and enhanced absorption coefficients upon annulation.

Stepwise Polychlorination of 8-Chloro-BODIPY and Regioselective Functionalization of 2,3,5,6,8-Pentachloro-BODIPY

“…3a,11 In agreement with these studies, BODIPY 5 reacted at room temperature with 1.1 equiv of phenol in the presence of potassium carbonate to give the 8-phenoxy-BODIPY 6c in 85% yield. Increasing the amount of phenol to 10 equiv gave the 3,5,8-triphenoxy-BODIPY 7c in 91% yield, as confirmed by 1 H NMR (see the Supporting Information).…”

“…The regioselective electrophilic bromination of the 1,2,3,5,6,7-positions of BODIPY has recently been reported using either bromine or N -bromosuccinimide (NBS) at room temperature or below. 3 On the other hand, the direct chlorination of the BODIPY core using N -chlorosuccinimide (NCS) can lead to mixtures of polychlorinated products that are difficult to purify. In order to better control the regioselectivity of the reaction, chlorination has been performed on the dipyrromethane or pyrrole precursors, and a variety of chlorinated derivatives have been reported using these methodologies.…”

“…On the other hand, increasing the temperature to reflux and using a stronger acid (H 2 SO 4 ) in place of acetic acid led only to BODIPY decomposition. Nevertheless, BODIPY 5 can be further functionalized at the 1,7-positions under more vigorous conditions, for example, using a large excess of bromine, 3a and these reactions are currently under investigation.…”

Synthesis of BODIPY dyes through postfunctionalization of the boron dipyrromethene core

“…The group of Jiao used an intramolecular direct arylation of 2,6-dibromoBODIPY derivatives to synthesize indole-annulated boron dipyrrins. 259 The method was based on a regioselective SNAr reaction of 2,3,5,6-tetrabromoBODIPY 122 with aryl amines (at the -positions), followed by Pdcatalyzed intramolecular C-C coupling ring fusion. The starting 2,3,5,6-tetrabromoBODIPY 122 was exclusively synthesized from 22 (with Ar = mesityl) in 90% yield using six equiv.…”

Selectfluor-Mediated Benzo[d][1,2,3]Triazole Functionalisation of 4,4-Difluoro-4-Bora-3a,4a-Diaza-s-Indacene

“…7 The transition metal-catalysed amination of BODIPY halides with amines or nitrogen-containing heterocycles and the transition metal-promoted direct C-H amination of BODIPYs are efficient synthetic methods for the facile functionalisation of BODIPY, which can be used in biomolecular probes. 8,9 Both of these methods need the use of transition metals and bases, which make them uneconomic to prepare. As a result, the successful development of new synthetic methods for this class of structures would be of great interest.…”