Straightforward Acid‐Catalyzed Synthesis of Pyrrolyldipyrromethenes

Abstract

Pyrrol hoch drei: Pyrrolyldipyrromethene mit verschiedenen funktionellen Gruppen wurden effizient durch POCl3‐vermittelte Kondensation von 5‐Chlor‐2‐formylpyrrolen oder ‐isoindolen mit geeigneten Pyrrol‐ oder Indolfragmenten synthetisiert. Dabei kommt es zu einer neuartigen nucleophilen aromatischen Substitution des anfänglich gebildeten protonierten Azafulvenrings.

Red‐to‐Near‐Infrared Emitting PyrrolylBODIPY Dyes: Synthesis, Photophysical Properties and Bioimaging Application

“…In addition, the values of N−H⋅F distances for 3‐pyrrolylBODIPY 3 ba are found to be 2.0509(13) and 2.5940(15) Å, respectively. All these values are in consistence with those reported for the limited accessible 3‐pyrrolylBODIPYs [18a,d] …”

Tetrafluorobenzo-Fused BODIPY: A Platform for Regioselective Synthesis of BODIPY Dye Derivatives

“…The 19 F NMR spectra of these compounds (see the Supporting Information) showed two different multiplet signals for the two fluorines linked to the boron atom, confirming a hydrogen bonding interaction between the fluorine atoms linked to the boron and the N-hydrogen of the peripheral pyrrole, as previously observed. 9d,14d Moreover, in the 1 H NMR spectra of both 3a and 4a (see the Supporting Information and Figure 2), one of the methyl groups corresponding to the pyrrolic substituent shows a signal that is clearly split into two singlets, and a similar split is also observed in the case of one of the two pyrrolic N-hydrogens. Therefore, we hypothesize that the first pyrrole unit introduced at the 3-position can also have a hydrogen bonding interaction with the α fluorine group of the adjacent benzo-fused ring, in both cases forming a seven-membered ring structure; the two structures coexist in solution in the time scale of the 1 H NMR experiment, causing the splitting of the signals as shown in Figure 2.…”

“…9a,21 Furthermore, no fluorescence emission was detected for 3a and 4a in THF, as previously reported for 3-pyrrole substituted isoindole BODIPYs, due to the solvent polarity. 14 However, in nonpolar solvents such as hexane and toluene, these types of compounds typically show high fluorescence quantum yields. In addition, 4a showed the most red-shifted absorption spectrum, 130 nm shift compared with starting BODIPY 1, due to the significant enhancement of the π -electron delocalization system, in part as a result of the pyrrolic NH⋯F hydrogen bond.…”

“…Among the possible solutions to this issue, BODIPYs with an aromatic ring fused at the β, β′ -pyrrolic positions are particularly interesting, since they generally provide highly planar BODIPY platforms featuring largely red-shifted absorptions and emissions, as well as enhanced hydrophobicity and cell permeability. 11,12 Recently, much research has been directed at the discovery of new synthetic pathways to introduce benzo-fused rings in the BODIPY scaffold, mainly using 4,5,6,7-tetrahydroisoindole, 8d,12 norbornane-derived pyrroles, 13 or 3-halogeno-1-formyliso-indoles 14 as reagents (Scheme 1), where only the last example represents a route not requiring harsh conditions.…”

Accessing the Ene–Imine Motif in 1H-Isoindole, Thienopyrrole, and Thienopyridine Building Blocks

“…Interestingly, NMR spectroscopy shows that the N–H resonance appears at 12.4 ppm, indicating that a six-membered ring hydrogen bonding motif forms between the amide and the pyrrole nitrogen. 20 Compound 22 , which features an extended conjugation pathway from vinyl moiety to a lactam carbonyl, is surprisingly stable to photochemical isomerization and thermal decomposition.…”