Click Nucleophilic Conjugate Additions to Activated Alkynes: Exploring Thiol-yne, Amino-yne, and Hydroxyl-yne Reactions from (Bio)Organic to Polymer Chemistry

The 1,4-conjugate addition reaction between activated alkynes or acetylenic Michael acceptors and nucleophiles (i.e., the nucleophilic Michael reaction) is a historically useful organic transformation. Despite its general utility, the efficiency and outcomes can vary widely and are often closely dependent upon specific reaction conditions. Nevertheless, with improvements in reaction design, including catalyst development and an expansion of the substrate scope to feature more electrophilic alkynes, many examples now present with features that are congruent with Click chemistry. Although several nucleophilic species can participate in these conjugate additions, ubiquitous nucleophiles such as thiols, amines, and alcohols are commonly employed and, consequently, among the most well developed. For many years, these conjugate additions were largely relegated to organic chemistry, but in the last few decades their use has expanded into other spheres such as bioorganic chemistry and polymer chemistry. Within these fields, they have been particularly useful for bioconjugation reactions and step-growth polymerizations, respectively, due to their excellent efficiency, orthogonality, and ambient reactivity. The reaction is expected to feature in increasingly divergent application settings as it continues to emerge as a Click reaction.

Multicomponent Polymerization for π-Conjugated Polymers

Structurally complex π-conjugated polymers hold great promise as key components in sensor and electronic devices; however, their syntheses have not been a trivial task. From a synthetic efficiency perspective, it would be more attractive to access these materials using convenient and efficient methods from simple building blocks. One such synthetic tool, multicomponent polymerization, can accommodate modularity and provide highly efficient syntheses. This feature article outlines several multicomponent polymerization strategies for the synthesis of various π-conjugated polymers, which are classified based upon how the monomers are aligned during polymerization. Additionally, the challenges and outlooks of this field are highlighted and discussed.

Access to molecular complexity. Multicomponent reactions involving five or more components

The evaluation of the significance of a chemical transformation addresses many factors, including such important characteristics as the number of chemical bonds formed in one step, the reaction time, labour intensity, the cost of reactants and catalysts and so on. The amount of waste produced in the reaction has also gained increasing importance in recent years. Multicomponent reactions (MCRs) occupy a special place as a synthetic tool in modern organic chemistry. These reactions allow the synthesis of target products with complex structures, minimizing labour costs. This review summarizes the literature on multicomponent reactions involving five or more components. The data in the review are classified according to the number of reactants participating in the reaction and the types of reactions. It is worth noting that in some cases, these transformations can be a part of a domino process, making this classification difficult, if not impossible. The structural diversity of the reaction products greatly increases with increasing number of components involved in the MCR, which becomes virtually unlimited when using combinations of MCRs. This review highlights the main trends of past decades in the field of MCRs. The last two decades have witnessed an explosive growth in the number of publications in this area of chemistry.

The bibliography includes 309 references.

Construction of 2,3-disubstituted benzo[b]thieno[2,3-d]thiophenes and benzo[4,5]selenopheno[3,2-b]thiophenes using the Fiesselmann thiophene synthesis

A series of 3-(hetero)aryl-substituted benzo[b]thieno[2,3-d]thiophenes, bearing various electron withdrawing groups at C-2 position of their scaffolds, were obtained using a convenient approach based on the Fiesselmann thiophene synthesis. To realize this strategy, the Friedel-Crafts acylation of (hetero)arenes with easily accessible 3-chlorobenzo[b]thiophene-2-carbonyl chlorides was initially performed to afford 3-chloro-2-(hetero)aroylbenzo[b]thiophenes. The latter ketones were treated either with methyl thioglycolate in the presence of DBU and calcium oxide powder or successively with sodium sulfide, an alkylating agent, containing methylene active component, and also DBU and calcium oxide, to form the desired benzo[b]thieno[2,3-d]thiophene derivatives. In addition, similar benzo[4,5]selenopheno[3,2-b]thiophene derivatives were prepared in the same manner using 3-bromobenzo[b]selenophen-2-yl substrates. The obtained functional derivatives of both benzo[b]thieno[2,3-d]thiophene and benzo[4,5]selenopheno[3,2-b]thiophene are of interest for further elaboration of organic semiconductor materials.

Acyl Sonogashira Cross-Coupling: State of the Art and Application to the Synthesis of Heterocyclic Compounds

The acyl Sonogashira reaction represents an extension of Sonogashira cross-coupling to acid chlorides which replace aryl or vinyl halides, while terminal acetylenes are used as coupling partners in both reactions. The introduction of a carbonyl functional group on the alkyne backbone determines a radical change in the reactivity of the products. Indeed, α,β-alkynyl ketones can be easily converted into different heterocyclic compounds depending on the experimental conditions employed. Due to its potential, the acyl Sonogashira reaction has been deeply studied with particular attention to the nature of the catalysts and to the structures of both coupling compounds. Considering these two aspects, in this review, a detailed analysis of the literature data regarding the acyl Sonogashira reaction and its role in the synthesis of several heterocyclic derivatives is reported.

Thio-Michael addition of thioamides and allenes for the selective construction of polysubstituted 2-arylthiophenes via TBAI/H2O2 promoted tandem oxidative annulation and 1,2-sulfur migration

A novel TBAI-catalyzed tandem thio-Michael addition/oxidative annulation of allenes and thioamides for the construction of polysubstituted 2-arylthiophenes under a sulfur migration transformation protocol has been developed. The transition-metal-free protocol achieves the oxidative cyclization reaction of thioamides containing electron-rich substituents with allenes to construct polysubstituted thiophenes selectively by controlling oxidation conditions.

Thiophene Syntheses by Ring Forming Multicomponent Reactions

Thiophenes occur as important building blocks in natural products, pharmaceutical active compounds, and in materials for electronic and opto-electronic devices. Therefore, there is a considerable demand for efficient synthetic strategies for producing these compounds. This review focuses on ring-forming multicomponent reactions for synthesizing thiophenes and their derivatives.

Multicomponent syntheses of functional chromophores

Multicomponent reactions are a valuable tool for the synthesis of functional π-electron systems. Two different approaches can be taken into account for accessing the target structures. In the more conventional scaffold approach an already existing chromophore is coupled with other components to give a complex functional π-system. Here, electronically monotonous components can also be introduced, which may exert synergistic electronic effects within the novel compound. The more demanding chromophore concept generates a complete π-electron system and a scaffold concurrently. The latter approach is particularly stimulating for methodologists since π-systems might be accessible from simple starting materials. This review encompasses the advances in the preparation of functional π-electron systems via multicomponent processes during the past few years, based both on the scaffold and chromophore concepts. Besides the synthetic strategies the most important properties, i.e. redox potentials, absorption and emission maxima or fluorescence quantum yields, of the synthesized molecules are highlighted.

Metal-free Brønsted acid mediated synthesis of fully substituted thiophenes via chemo- and regioselective intramolecular cyclization of α,α′-bis(β-oxodithioesters) at room temperature

Metal-free Brønsted acid mediated synthesis of tetrasubstituted thiophenes via intramolecular cyclization of α,α′-bis(β-oxodithioesters) is devised at room temperature.

Direct synthesis of polysubstituted 2-aminothiophenes by Cu(II)-catalyzed addition/oxidative cyclization of alkynoates with thioamides

A facile and direct synthetic method was developed for the construction of structurally important 2-aminothiophenes in moderate to excellent yields (up to 91%), via Cu(II)-catalyzed addition/oxidative cyclization of readily available thioamides with alkynoates under an air atmosphere.

Synthesis of 2,3-disubstituted thiophenes from 2-aryl-3-nitro-cyclopropane-1,1-dicarboxylates and 1,4-dithiane-2,5-diol

A two-step synthesis of 2,3-disubstituted thiophenes from trans-2-aryl-3-nitrocyclopropane-1,1-dicarboxylates and 1,4-dithiane-2,5-diol is described.

Diversity-oriented synthesis of intensively blue emissive 3-hydroxyisoquinolines by sequential Ugi four-component reaction/reductive Heck cyclization

A convergent approach to highly functionalized 3-hydroxyisoquinolines is reported. The key steps are an Ugi multicomponent reaction and a subsequent intramolecular reductive Heck reaction; these can also be performed as a one-pot procedure. The structures display very interesting properties as blue-fluorescence emitters. Photophysical studies on the absorption and static fluorescence indicate that the substitution pattern on the pyridyl part influences the optical properties only to a minor extent, unless the amide substituent becomes sterically demanding and leads to significant nonradiative deactivation. The donor substitution on the benzo core considerably enhances the fluorescence quantum yields and trimethoxy substitution causes a pronounced redshift of the emission bands. Protonation of the isoquinolyl nitrogen atom causes efficient static quenching of the fluorescence.

Recent advances in the synthesis of thiophene derivatives by cyclization of functionalized alkynes

This review is intended to highlight some recent and particularly interesting examples of the synthesis of thiophene derivatives by heterocyclization of readily available S-containing alkyne substrates.