Synthesis of Tetrasubstituted Alkenes by Stereo- and Regioselective Stannyllithiation of Diarylacetylenes

Post-Formation of Fused Pentagonal Structure on Fjord Region of Polyaromatic Hydrocarbons under Hydrothermal Conditions

This study explores the synthesis of cyclopenta-fused polyaromatic hydrocarbons (CP-PAHs) via Pt-catalyzed cyclization in water, focusing on the formation of fused pentagonal rings within heavily fused PAH frameworks. Utilizing platinum catalysts at lower temperatures (200-260 °C) in water, led to the successful synthesis of singly cyclized CP-PAHs. The reaction conditions facilitated the mono-cyclization of substrates such as dibenzo[g,p]chrysene and its isomers, yielding the desired products while suppressing the formation of bis-cyclized compounds. The use of Fe2O3 as an additive in conjunction with PtO2 was effective to suppress hydrogenation of the substrates and products. The products exhibited a redshift in UV-visible absorption and photoluminescence bands due to a decrease in the HOMO-LUMO energy gap. These findings highlight the potential of Pt-catalyzed cyclization for the controlled synthesis of CP-PAHs, with implications for various applications in materials science.

Chemo-, regio- and stereoselective access to polysubstituted 1,3-dienes via Nickel-catalyzed four-component reactions

1,2-Difunctionalization of alkynes offers a straightforward approach to access polysubstituted alkenes. However, simultaneous multi-component cascade transformations including difunctionalization of two alkynes with both syn- and anti-selectivity in one catalyst system is undeveloped and proves to be a significant challenge. Herein, we report a Nickel-catalyzed four-component reaction to access polysubstituted 1,3-dienes using two terminal alkynes, aryl boroxines, and perfluoroalkyl iodides, wherein the reaction forms three new C-C bonds in a single vessel and serve as a modular strategy to access polysubstituted 1,3-dienes with excellent chemoselectivity, good regioselectivity and exclusive stereoselectivity. Control experiments reveal the plausible reaction mechanism and DFT calculations explain the cause for the formation of this unusual four-component reaction. Furthermore, we successfully incorporate two biologically active units into 1,2,3,4-tetrasubstituted 1,3-dienes, which greatly increases the diversity of molecular scaffolds and brings more potential values to medicinal chemistry, the synthetic utility of our protocol is further demonstrated by the late-stage transformations.

Asymmetric anti-Selective Borylalkylation of Terminal Alkynes by Nickel Catalysis

Selective transformation of alkyne triple bonds to double bonds serves as an efficient platform to construct substituted alkenes. While significant advances have been made in its spatiotemporal regulation, achieving a multicomponent enantioselective reaction that requires multifaceted selectivity issues to be overcome is still uncommon. Here, we report an unprecedented asymmetric anti-stereoselective borylcarbofunctionalization of terminal alkynes by nickel catalysis. The utilization of an inexpensive chiral diamine ligand enables the three-component cross-coupling of terminal alkynes, a diboron reagent, and prochiral alkyl electrophiles with high levels of regio-, stereo-, and enantioselectivities. This reaction provides an efficient protocol to access enantioenriched alkenyl esters bearing an α-stereogenic center, is remarkably practical, and has a broad scope and an outstanding functional group compatibility. In addition, the value of this method has been highlighted in a diversity of follow-up stereoretentive derivatizations and the stereoselective concise synthesis of complex drug molecules.

Diphenyl Ditelluride: An Unconventional Reducing Agent in the Sulfonylative Cascade of Alkynyl Cyclohexadienones

Herein, we report a reductive hydrazo-sulfonylative difunctionalization cascade of alkynyl cyclohexadienones employing PhTeTePh as an uncommon reducing agent. Diphenyl ditelluride is a commercially available solid with a good solubility profile in most organic solvents, and this is the first report illustrating it as a reducing agent. The protocol afforded a variety of difunctionalized dihydrochromenones and dihydrobenzofuranones in good yields under relatively mild conditions. The reactions were scalable, and mechanistic studies were conducted to probe the reaction mechanism. Additionally, photophysical studies of the products were carried out, which revealed that they had significant absorption (400-450 nm) and emission (520-570 nm) in the visible region.

Electrochemical and spectroscopic properties of twisted dibenzo[g,p]chrysene derivatives

Dibenzo[g,p]chrysene (DBC), which consists of a twisted naphthalene core with four fused benzene rings, is a promising framework for organic electronic materials. Therefore, the research for structure–property relationships is important for the design of DBC-based materials. Here, the electrochemical and spectroscopic properties of DBC derivatives were investigated, and the effects of substituents and torsion of the naphthalene moiety were examined based on density functional theory (DFT) calculations. All the substituted DBC derivatives showed higher oxidation potentials than that for DBC-H, even for compounds that contained an electron-donating group such as DBC-Me and DBC-SMe. DFT calculations clearly indicate that these higher oxidation potentials are due to the ineffective conjugation of the MeO group, which is oriented perpendicular to the benzene ring because of the steric repulsion of substituents on both sides. More specifically, the inductive effect of the MeO group is dominant rather than the mesomeric effect when the substituent is located at both sides of the MeO group. Concerning the torsion of the naphthalene moiety, the twisting results in a slight increase in the HOMO and a slight lowering of the LUMO. The twisting effect is much smaller than the conjugation effect of the MeO group. Absorption spectra of all the substituted DBC derivatives also showed a red-shift as compared to that for DBC-H. Concerning the luminescence, a strong photoluminescence was observed for DBC-H and DBC-Si.

Recent advances in the stereoselective synthesis of acyclic all-carbon tetrasubstituted alkenes

Alkenes bearing four carbon-based groups are ubiquitous motifs in chemical sciences due to their various applications from medicinal to materials chemistry, and as chemical platforms for the synthesis of complex, chiral molecules. As such, tremendous research efforts are currently ongoing in order to develop general procedures for the challenging stereoselective synthesis of all-carbon tetrasubstituted alkenes, especially for acyclic structures. Since classical approaches to carbon-carbon double bonds are not suitable for the high steric demand around tetrasubstituted alkenes, a variety of unique approaches to access these privileged functional groups have been developed in recent years. This review article highlights the most significant developments in the field from 2007 to 2020, with an emphasis on the mechanisms and remaining limitations of these contemporary methods. Specifically, recent advances in internal alkyne carbofunctionalizations, in multicomponent couplings or other cross-couplings from nucleophilic or electrophilic alkenyl partners, and in the development of miscellaneous methods, are discussed.

Synthesis of extended polycyclic aromatic hydrocarbons by oxidative tandem spirocyclization and 1,2-aryl migration

The extended polycyclic aromatic hydrocarbons (PAHs) have received significant interdisciplinary attention due to their semiconducting applications in diverse organic electronics as well as intriguing structural interests of well-defined graphene segments. Herein, a highly efficient oxidative spirocyclization and 1,2-aryl migration tandem synthetic method for the construction of extended polyaromatic hydrocarbons (PAHs) has been developed. The CuCl-catalyst/PhCO₃ ^tBu or DDQ oxidation system in the presence of trifluoroacetic acid enables the selective single-electron oxidation to take place preferentially at the more electron-rich alkene moiety of o-biphenylyl-substituted methylenefluorenes, giving rise to the subsequent tandem process. A variety of structurally diverse extended PAHs including functionalized dibenzo[g,p]chrysenes, benzo[f]naphtho[1,2-s]picene, hexabenzo[a,c,fg,j,l,op]tetracene, tetrabenzo[a,c,f,m]phenanthro[9,10-k]tetraphene, tetrabenzo[a,c,f,k]phenanthro[9,10-m]tetraphene, tetrabenzo[a,c,f,o]phenanthro[9,10-m]picene and S-type helicene have been readily synthesized.

Simple synthetic routes to polyaromatic hydrocarbons are important due to their applications in organic electronics. Here the authors report a straightforward synthesis of a diverse range of polyaromatic hydrocarbons, via a one-pot oxidative cyclisation and subsequent 1,2-aryl migration.

Synthesis of Multisubstituted Olefins through Regio- and Stereoselective Addition of Interelement Compounds Having B-Si, B-B, and Cl-S Bonds to Alkynes, and Subsequent Cross-Couplings

Multisubstituted olefins are fundamental motifs in organic compounds. In this account, we describe the synthesis of organic molecules bearing an olefinic moiety by the transition-metal-catalyzed regio- and stereoselective addition of a variety of interelement compounds to alkynes. Regio- and stereoselective silaboration, diborylation, and chlorothiolation have been achieved by using the transition-metal catalysts. The subsequent cross-coupling reactions of the boron-containing alkenes to install various aryl groups afforded the corresponding tri- and tetraarylated olefins. This account describes our research on the highly regio- and stereoselective synthesis of multifunctionalized olefins such as tetraarylethenes with four different aryl groups.

Iron-catalyzed regio- and stereoselective chlorosulfonylation of terminal alkynes with aromatic sulfonyl chlorides

Terminal alkynes react with aromatic sulfonyl chlorides in the presence of an iron(II) catalyst and a phosphine ligand to give (E)-β-chlorovinylsulfones with 100% regio- and stereoselectivity. Various functional groups, such as chloride, bromide, iodide, nitro, ketone, and aldehyde, are tolerated under the reaction conditions. Addition of tosyl chloride to a 1,6-enyne followed by radical 5-exo-trig cyclization gave an exocyclic alkenylsulfone.