Helically and Linearly Fused Rylenediimide-Hexabenzocoronenes

Perylene- as well as naphthalenediimides were fused to hexabenzocoronenes (HBCs) at their imide position to realize highly π-extended donor-acceptor (D-A)-hybrids. Successful isomer separation in the first step was decisive to guarantee a straightforward synthetic sequence. Hexaphenylbenzenes as precursors were accessed via Diels-Alder reactions and reacted in a Scholl oxidation to yield the respective HBC derivatives. The fully conjugated benzimidazole linker, which separates the electron donating HBC from the electron accepting rylenediimide, enabled the formation of either a linear or a helical configuration. Largely different chemical, physical, and optoelectrical characteristics were noted for the two configurations. What stood out was their aggregation and their excited state deactivation depending on the solvent polarity. Results from global analysis of the femtosecond transient absorption data corroborated the formation of a charge-transfer (CT) state that is stabilized in the helically fused configuration relative to the linear analogue. However, a comparison with spectroelectrochemical experiments failed to disclose evidence for a charge-separated (CS) state.

Direct Metal-Free Transformation of Alkynes to Nitriles: Computational Evidence for the Precise Reaction Mechanism

Density functional theory calculations elucidated the precise reaction mechanism for the conversion of diphenylacetylenes into benzonitriles involving the cleavage of the triple C≡C bond, with N-iodosuccinimide (NIS) as an oxidant and trimethylsilyl azide (TMSN3) as a nitrogen donor. The reaction requires six steps with the activation barrier ΔG‡ = 33.5 kcal mol-1 and a highly exergonic reaction free-energy ΔGR = -191.9 kcal mol-1 in MeCN. Reaction profiles agree with several experimental observations, offering evidence for the formation of molecular I2, interpreting the necessity to increase the temperature to finalize the reaction, and revealing thermodynamic aspects allowing higher yields for alkynes with para-electron-donating groups. In addition, the proposed mechanism indicates usefulness of this concept for both internal and terminal alkynes, eliminates the option to replace NIS by its Cl- or Br-analogues, and strongly promotes NaN3 as an alternative to TMSN3. Lastly, our results advise increasing the solvent polarity as another route to advance this metal-free strategy towards more efficient processes.

Copper-Mediated Conversion of Alkynes into Nitriles via Iodotriazoles

We disclose our studies on a copper-mediated reaction of alkynes with trimethylsilyl azide to afford nitriles, and proposed a reaction mechanism, which involves an iodoalkyne and an iodotriazole as intermediates.

Synthesis and crystal packing of perylene-derivatives with extreme sterically demanding pentaphenylbenzene bay-substituents

An unprecedented library of single and double bay-substituted perylene-pentaphenylbenzenes (PPBs) is presented. An extreme core-distortion as well as successful elimination of aggregation interactions of perylenes was confirmed by X-ray analysis. The isomerically pure perylene-PPB hybrids show remarkable differences in their photophysical properties with respect to their regiochemistry as well as different peri-functionalization.

Highly Conjugated π-Systems Arising from Cannibalistic Hexadehydro-Diels-Alder Couplings: Cleavage of C-C Single and Triple Bonds

We have investigated the cannibalistic self-trapping reaction of an ortho-benzyne derivative generated from 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne in an HDDA reaction. Without adding any specific trapping agent, the highly reactive benzyne is trapped by another bisdiyne molecule in at least three different modes. We have isolated and characterized the resulting products and performed high-level calculations concerning the reaction mechanism. During the cannibalistic self-trapping process, either a C≡C triple bond or an sp-sp3 C-C single bond is cleaved. Up to seven rings and nine C-C bonds are formed starting from two 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne molecules. Our experiments and calculations provide considerable insight into the variety of reaction pathways which the ortho-benzyne derivative, generated from a bisdiyne, can take when reacting with another bisdiyne molecule.

Arylacetylenes as two-carbon synthons: synthesis of eight-membered rings via C[triple bond, length as m-dash]C bond cleavage

The first synthesis of eight-membered N-containing heterocycles by oxidative bicyclization/ring extension of arylacetylenes and aryl amines has been achieved. This protocol uses arylacetylene as an unusual two-carbon synthon by incorporating the two parts of the cracked C[triple bond, length as m-dash]C bond into the final product, which provides a new method for using arylacetylenes as two-carbon synthons and further enriches C[triple bond, length as m-dash]C bond cleavage methodology. Moreover, this multi-component reaction can provide diverse fused elegant eight-membered N-heterocycles under mild conditions with wide substrate scopes.

Fluorescent Donor-Acceptor Psoralen Cruciforms by Consecutive Suzuki-Suzuki and Sonogashira-Sonogashira One-Pot Syntheses

Two novel donor-acceptor cruciform topologies are efficiently synthesized by site-selective Suzuki-Suzuki and Sonogashira-Sonogashira multicomponent reactions starting from a bromo-triflato-functionalized psoralen scaffold. In addition to tunability of photophysical properties, such as absorption and emission, many derivatives possess partially high relative fluorescence quantum yields in solution and fluoresce strongly in the solid state. Additionally, the promising compounds show solvatochromism and acidochromic effects. In addition, 8-p-anisyl-5-p-cyanophenyl-substituted psoralen exhibits aggregation-induced emission properties. Experimentally (applying the Lippert-Mataga model) and computationally (TD-DFT calculations), the pronounced charge transfer character of the longest wavelength absorption band was confirmed.

Visible light-mediated photocatalytic oxidative cleavage of activated alkynes via hydroamination: a direct approach to oxamates

The direct oxidative cleavage of activated alkynes via hydroamination has been described using organic photocatalyst under visible-light irradiation at room temperature. In this reaction, the single electron oxidation of an in situ formed enamine followed by radical coupling with an oxidant finally delivers the oxamate. The key features of this photocatalytic reaction are the mild reaction conditions, metal-free organic dye as a photocatalyst, and TBHP playing a dual role as “O” source and for the regeneration of the photocatalyst.

The direct oxidative cleavage of activated alkynes via hydroamination has been described using organic photocatalyst under visible-light irradiation at room temperature.

Silver-Catalyzed Nitration/Annulation of α-Alkynyl Arylols toward 3-Nitrated Benzofurans

A silver-catalyzed nitration/annulation of α-alkynyl arylols is reported by using tert-butyl nitrite (TBN) as a NO₂ radical precursor, from which a set of 3-nitrated benzofurans were synthesized with moderate to good yields. This transformation initiated by an in situ generated NO₂ radical proceeds efficiently under mild and neutral redox conditions, which provides a new pathway toward the 3-nitrobenzofuran framework via catalytic difunctionalization of internal alkynes.

tert-Butyl Nitrite Mediated Synthesis of Fluorinated O-Alkyloxime Ether Derivatives

A tert-butyl nitrite (TBN)-mediated synthesis of fluorinated O-alkyloxime ether derivatives with bromodifluoroalkyl reagents as the fluorine sources has been developed. A variety of halodifluorinated compounds were found compatible, delivering the desired products in moderate to excellent yields. This transformation features a simple operation, can be done in air, and found to involve radicals. This protocol represents a straightforward approach to access various fluorinated O-alkyloxime ether derivatives.

Direct Transformation of Terminal Alkynes into Amidines by a Silver-Catalyzed Four-Component Reaction

An unprecedented conversion of terminal alkynes into N-sulfonimidamides (amidines) is reported by a silver-catalyzed, one-pot, four-component reaction with TMSN₃, sodium sulfinate, and sulfonyl azide. The reaction scope includes both aromatic and aliphatic alkynes. A possible cascade reaction mechanism, consisting of alkyne hydroazidation, sulfonyl radical addition, 1,3-dipolar cycloaddition by TMSN₃, and retro-1,3-dipolar cycloaddition, is proposed. TMSN₃ is found to play an essential role in each step of the reaction.

Transformations of alkynes to carboxylic acids and their derivatives via C[triple bond, length as m-dash]C bond cleavage

Alkynes are building blocks of high synthetic value and their usefulness as precursors to many chemical and biological systems is widely established. Amongst several transformations of alkynes, cleavage of the C[triple bond, length as m-dash]C bond for obtaining diverse compounds is considered to be important. This review, in particular, comprehensively assimilates the transformations of alkynes to carboxylic acids including esters, amides and nitriles resulting from the cleavage of the C[triple bond, length as m-dash]C bond either under the influence of a metal catalyst or via a metal-free approach.

Cleavage of BN triple bonds by main group reagents

A silylene and a 1,2-diaminoalkyne respectively cleave the strong BN triple bond in iminoboranes.

Copper catalyzed cyanation through CC bond cleavage of gem-aryl dibromide followed by second cyanation of iodoarene by a released CN unit

A new approach for the synthesis of aryl cyanides through CC cleavage of styrenyl gem-dibromide has been achieved.

Monomer-induced switching of stereoselectivity and limitation of chain growth in the polymerization of amine-containing para-substituted phenylacetylenes by [Rh(norbornadiene)Cl]2

In the presence of [Rh(nbd)Cl]₂ alone, amine-containing phenylacetylenes can serve as both a monomer and cocatalyst in the polymerization. Moreover, the stereo-selectivity of the products was controlled by pendant groups.

N. SB, Patra SK. Synthesis, photophysical and concentration-dependent tunable lasing behavior of 2,6-diacetylenyl-functionalized BODIPY dyes

Extended π-conjugation through the 2- and 6-positions of the BODIPY core induces tunable yellow-red lasing with excellent efficiency of up to 41% in toluene.

Co-catalyzed highly selective C(sp3)–H nitration

A Co-catalyzed highly selective C(sp³)–H nitration via a radical pathway was disclosed, overcoming the strong coordination effect of pyrimidine by suppressing C(sp²)–H functionalization as well as proximity C(sp³)–H functionalization.