Classifications, properties, recent synthesis and applications of azo dyes.

Multicomponent reactions are flexible reactions for the rapid generation of complex molecules with often biologically relevant scaffold structures. Combined with the ease of parallelization and the exploratory power with regard to chemical space, multicomponent reactions have attracted significant attention from the medicinal chemistry community. In this Review, we present an overview of recent literature concerning this topic to provide insight into the applications of multicomponent reactions in this field.

Recent applications of multicomponent reactions in medicinal chemistry

The translation of small molecule chemistries into efficient methodologies for polymer functionalization spans several decades, enabling critical advances in soft matter materials synthesis with tailored and adaptive property profiles. The present Perspective explores—based on selected examples—50 years of innovation in polymer functionalization chemistries. These span a diverse set of chemistries based on activated esters, thiol–ene/yne processes, nucleophilic systems based on isocyanates, reactions driven by the formation of imines and oximes, ring-opening processes, cycloadditions, and—in a recent renaissance—multicomponent reactions. In addition, a wide variety of chain types and architectures have been modified based on the above chemistries, often with exquisite chemical control, highlighted by key examples. We conclude our journey through polymer functionalization with the—in our view—most critically required advances that have the potential to move from “science fiction” to “science fact”.

50th Anniversary Perspective: Polymer Functionalization

We have known of azobenzene for over 150 years, the past 80 of which have seen the study and application of its photochromism. Azobenzene derivatives are now considered archetypical molecular switches, and their stability and reliability make them amenable to many fields of modern chemistry, materials science, biology and photopharmacology. When developing a photoswitch for a given application, a common approach is to tune the properties of an azobenzene. It is also possible to instead use heteroaryl azo dyes — motifs that are less popular even though their diversity offers distinct features. Despite the first discoveries of switching behaviour in heteroaryl azos and azobenzenes being coincident, the former have only recently begun to attract attention. This Review describes how the versatile and multifaceted characteristics of these scaffolds make them serious alternatives to azobenzene derivatives in molecular photoactuation. Heteroaryl azo photoswitches arguably deserve more consideration, and our survey of these systems includes challenges to their successful deployment. When presented with a light stimulus, heteroaryl azo photoswitches undergo molecular motion that can be harnessed for applications in materials science, catalyst design or drug development, among other fields. This Review describes selected subclasses of these versatile chemical motifs, covering their properties and prominent applications.

Heteroaryl azo dyes as molecular photoswitches

Developments in azo disperse dyes derived from heterocyclic diazo components

2-aminothiophenes by the gewald reaction

Synthesis and application of 2‐styryl‐6,7‐dichlorothiazolo[4,5‐b]‐quinoxaline based fluorescent dyes: Part 3

Synthesis of 2-N-(benzo[b]thiophen-2-yl)benzo and heterofused-1,2,3-triazoles

Synthesis of azo benzo[b]thiophene derivatives and their application as disperse dyes

Synthesis of 2-(hetaryl or aryl)-azo thiophene derivatives (IVa–IVg) was achieved by diazotisation of ethyl 2-amino-3-cyano-5-carbethoxy thiophene-4-acetic acid ester (I) using nitrosyl sulphuric acid, coupling with suitable heterocyclic hydroxy and N, N-dialkyl-substituted aryl amines, which resulted in thiophene azo dyes. The key intermediate (I), used as the diazonium component was synthesised in one pot and in excellent yield from diethyl acetone dicarboxylate, sulphur and malononitrile, using diethylamine as a catalyst, following the Gewald Synthesis. The spectral properties of these dyes were studied. The dyes when applied as disperse dyes on polyester fibres gave excellent results.

Dinesh W. Rangnekar

Papers

2-aminothiophenes by the gewald reaction

Synthesis and application of 2‐styryl‐6,7‐dichlorothiazolo[4,5‐b]‐quinoxaline based fluorescent dyes: Part 3

Synthesis of 2-N-(benzo[b]thiophen-2-yl)benzo and heterofused-1,2,3-triazoles

Synthesis of azo benzo[b]thiophene derivatives and their application as disperse dyes

Synthesis of 2-azo-3-cyano-5-carbethoxy thiophene derivatives and their application on polyester fibres