Toward unidirectional switches: 2-(2-Hydroxyphenyl)pyridine and 2-(2-methoxyphenyl)pyridine derivatives as pH-triggered pivots

Niu

Chemistry An Asian Journal

et al. 2018

The significant progress recently achieved in designing smart acid-responsive materials based on intramolecular charge transfer inspired us to utilize excited-state intramolecular proton transfer (ESIPT) for developing a turn-on acid-responsive fluorescent system with an exceedingly large Stokes shift. Two ESIPT-active fluorophores, 2-(2-hydroxyphenyl)pyridine (HPP) and 2-(2-hydroxyphenyl)benzothiazole (HBT), were fused into a novel dye (HBT-HPP) fluorescent only in the protonated state. Moreover, we also synthesized three structurally relevant control compounds to compare their steady-state fluorescence spectra and optimized geometric structures in neutral and acidic media. The results suggest that the fluorescence turn-on was caused by the acid-induced shift of the ESIPT-responsible intramolecular hydrogen bond from the HPP to HBT moiety. This work presents a systematic comparison of the emission efficiencies and basicity of HBT and HPP for the first time, thereby utilizing their differences to construct an acid-responsive smart organic fluorescent material. As a practical application, red fluorescent letters can be written using the acid as an ink on polymer film.

Section: Photophysicalp Roperties and Theoretical Calculations Of Hbtsupporting

confidence: 64%

Section: Resultsmentioning

confidence: 73%

Acid‐Induced Shift of Intramolecular Hydrogen Bonding Responsible for Excited‐State Intramolecular Proton Transfer

Niu

Chemistry An Asian Journal

et al. 2018

Beilstein J. Org. Chem.

“…Considering further applications of atropisomeric arylated pyridines in the design of new materials like molecular switches [ 4 ], it would be desirable to estimate their thermal stability. We therefore performed kinetic experiments in order to establish the value of the barrier to rotation in the atropisomerisation process by using a dynamic 1 H NMR spectroscopy carried out on more unstable syn atropisomers, which are ( syn )- 7 and ( syn )- 10 .…”

Section: Resultsmentioning

confidence: 99%

“…Axially chiral biaryls not only subsist in many classes of natural and bioactive compounds [ 1 – 2 ] but also are an essential stereochemical element of many popular, commercially available chiral catalysts [ 3 ]. Several ortho -substituted arylpyridine derivatives belong to a very important class of axially chiral compounds which have gained interest due to their role as chiral ligands in cross-coupling reactions, or being interesting molecules with important electrochemical, photochemical, including light-activated unidirectional motion properties [ 4 – 9 ]. It is therefore not surprising that important advances have been made in the synthesis of various classes of axially chiral organic compounds over the past decade [ 10 – 13 ].…”

Section: Introductionmentioning

confidence: 99%

Some mechanistic aspects regarding the Suzuki–Miyaura reaction between selected ortho-substituted phenylboronic acids and 3,4,5-tribromo-2,6-dimethylpyridine

Pomarański

Roszkowski

Maurin

et al. 2018

Background: Atropisomers are very interesting stereoisomers having axial chirality resulting from restricted rotation around single bonds and are found in various classes of compounds. ortho-Substituted arylpyridines are an important group of them. A regio- and atropselective Suzuki–Miyaura cross-coupling reaction on 3,4,5-tribromo-2,6-dimethylpyridine was studied. Results: Reactions with various amounts of ortho-substituted phenylboronic acids with 3,4,5-tribromo-2,6-dimethylpyridine gave a series of mono- di- and triarylpyridine derivatives which allowed to draw conclusions about the order of substitution. Also, the observed selectivity in the case of ortho-methoxyphenylboronic acid suggested an additional metal O-chelation effect in the transition state, apparently not present in the ortho-chloro analogues. The rotational barrier in selected atropisomers was determined on the basis of HT NMR and thermal epimerisation experiments. The structure of most presented atropisomeric derivatives of 2,6-dimethylpyridine was confirmed by single-crystal X-ray analysis. Racemic chiral, differently substituted atropisomers were also examined by 1H NMR spectroscopy in the presence of a chiral solvating agent. Conclusion: This regio- and atropselectivity may be generally applicable to other arylpyridine systems. A regio- and atropselective Suzuki–Miyaura cross-coupling process has been observed, giving an efficient access to a class of atropisomeric compounds. An opposite selectivity using a differently ortho-substituted phenylbornic acid was observed.

“…66 Also, some arylpyridines have received attention due to relevant electrochemical and photochemical properties and they were found to be useful as building blocks for the design of polymers or complexes. [67][68][69][70][71][72][73][74][75][76][77][78][79] Several atropisomeric arylpyridine derivatives exhibit interesting kinetic time-dependent properties. At certain temperatures, defined by stereoelectronic factors present in the molecule, rotation around the single bond that is the stereogenic axis occurs, thus causing atropisomerization.…”

Section: Figure 7 Selected Examples Catalyst Agent Having Pyridine Corementioning

confidence: 99%

Arylpyridines: A Review from Selective Synthesis to Atropisomerism

Pomarański

Czarnocki²

2018

Synthesis

Multiply arylated heterocycles are interesting structures with highly useful functions and fascinating optoelectronic and biological properties. Pyridines are an important class of compounds, playing a role in various fields of chemistry. When the pyridine ring is connected to other aromatic systems, novel stereochemical outcomes may arise. This work summarizes different methodologies applied for the synthesis of substituted arylpyridine derivatives and summarizes stereochemical phenomena resulting from atropisomerism present in certain arylated pyridines.1 Introduction2 Arylpyridines Containing meta- and para-Substituted Phenyl Groups2.1 Arylpyridine Derivatives as Amphetamine Analogues Markers2.2 Site-Selective Synthesis of Arylpyridines3 Atropisomerism in Arylpyridines Containing ortho-Substituted Phenyl Groups3.1 Synthesis of Arylpyridines Containing ortho-Substituted Phenyl Groups3.2 Other Methods for the Preparation of Arylated Pyridines4 Fully Substituted Pyridine Derivatives4.1 Site-Selective Synthesis of Fully Arylated Pyridines4.3 Atropisomerism in Densely Substituted Arylpyridines Containing ortho-Substituted Phenyl Groups5 Enantioselective Synthesis of Arylpyridine Derivatives6 Conclusion