Modular and Highly Stereoselective Approach to All-Carbon Tetrasubstituted Alkenes

Organophosphates as Versatile Substrates in Organic Synthesis

This review summarizes the applications of organophosphates in organic synthesis. After a brief introduction, it discusses cross-coupling reactions, including both transition-metal-catalyzed and transition-metal-free substitution reactions. Subsequently, oxidation and reduction reactions are described. In addition, this review highlights the applications of organophosphates in the synthesis of natural compounds, demonstrating their versatility and importance in modern synthetic chemistry.

Synthesis of highly substituted alkenes by sulfur-mediated olefination of N-tosylhydrazones

Tetraphenylethylenes (TPEs) are well-known for their aggregation-induced emission properties. The synthesis of TPE derivatives, as well as other highly substituted olefins, generally requires the use of hazardous reagents, such as metalorganic compounds, to overcome the high activation energies caused by the sterically congested double bond. Herein, we present an efficient and metal-free procedure for the synthesis of tetraarylethylenes via alkylidene-homocoupling of N-tosylhydrazones, derived from readily available benzophenones, in excellent yields. The method relies only on cheap and benign additives, i.e. elemental sulfur and potassium carbonate, and easily competes with other established procedures in terms of scope, yield and practicability. A mechanistic study revealed a diazo compound, a thioketone and a thiirane as key intermediates in the pathway of the reaction. Based on this, a modified method, which allows for selective alkylidene-cross-coupling, generating a broader scope of tri- and tetrasubstituted olefins in good yields, is showcased as well.

Palladium-Catalyzed Highly Chemo- and Stereoselective Bisthiolation of Terminal Alkynes with Allyl Phenyl Sulfides via C-S Bond Cleavage

A facile and general method for palladium-catalyzed stereoselective bisthiolation of terminal alkynes with allyl phenyl sulfides has been developed. The scope and versatility of the reaction have been demonstrated, and a broad range of substrates bearing electron-donating and -withdrawing groups on the aromatic rings were all compatible with this reaction, providing the desired (Z)-1,2-dithio-1-alkenes in moderate to good yields. Preliminary mechanistic studies demonstrated that the sulfur source of the desired products may be successively incorporated into alkynes via C-S bond cleavage of two molecules of allyl phenyl sulfides and ruled out the possibility of vinyl sulfides, alkynyl sulfides, and disulfide intermediates being involved in this reaction.

Stereoconvergent and -divergent Synthesis of Tetrasubstituted Alkenes by Nickel-Catalyzed Cross-Couplings

We report the development of a method to diastereoselectively access tetrasubstituted alkenes via nickel-catalyzed Suzuki-Miyaura cross-couplings of enol tosylates and boronic acid esters. Either diastereomeric product was selectively accessed from a mixture of enol tosylate starting material diastereomers in a convergent reaction by judicious choice of the ligand and reaction conditions. A similar protocol also enabled a divergent synthesis of each product isomer from diastereomerically pure enol tosylates. Notably, high-throughput optimization of the monophosphine ligands was guided by chemical space analysis of the kraken library to ensure a diverse selection of ligands was examined. Stereoelectronic analysis of the results provided insight into the requirements for reactive and selective ligands in this transformation. The synthetic utility of the optimized catalytic system was then probed in the stereoselective synthesis of various tetrasubstituted alkenes, with yields up to 94% and diastereomeric ratios up to 99:1 Z/E and 93:7 E/Z observed. Moreover, a detailed computational analysis and experimental mechanistic studies provided key insights into the nature of the underlying isomerization process impacting selectivity in the cross-coupling.

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.

Cross-Coupling Reactions of Double or Triple Electrophilic Templates for Alkene Synthesis

This short review summarizes the latest advances in the cross-coupling reactions of double and triple electrophilic templates bearing halogen atoms and an activated C–O bond. Reactions involving the formation of a C–C bond as part of di-, tri-, and tetrasubstituted double bond systems are highlighted.

1 Introduction

2 Cross-Coupling Reactions of Halovinyl Tosylates

3 Cross-Coupling Reactions of Halovinyl Triflates

4 Cross-Coupling Reactions of Halovinyl Phosphates

5 Cross-Coupling Reactions of Halovinyl Esters

6 Conclusion

Formation of trisubstituted buta-1,3-dienes and α,β-unsaturated ketones via the reaction of functionalized vinyl phosphates and vinyl phosphordiamidates with organometallic reagents

We studied the reactions of vinyl phosphates and vinyl phosphordiamidates containing an ester functional group with organometallic reagents. We found that the functionalized vinyl phosphates were smoothly converted into tri- and tetrasubstituted buta-1,3-dienes via the reaction with aryllithium reagents. Moreover, the vinyl phosphordiamidates were converted into α,β-unsaturated ketones using Grignard reagents. Based on the performed experiments, we proposed a reaction mechanism, which was confirmed by means of the isolation of key intermediates.

We studied the reactions of vinyl phosphates and vinyl phosphordiamidates containing an ester functional group with organometallic reagents.

Room-Temperature Negishi Reaction of Trisubstituted Vinyl Phosphates for the Synthesis of Tetrasubstituted Alkenes

The present study investigated the ability of bromovinyl phosphates to react with organozinc reagents at room temperature during palladium-catalyzed reactions. It was determined that both the bromine atom and the phosphate group were successfully substituted by means of the reaction with the organozinc reagents, thereby allowing for the synthesis of cyclic and acyclic tetrasubstituted double bonds. The low stability of the organozinc compounds in an acidic environment was exploited to accomplish the synthesis of alkenes using a one-pot, two-step experimental setup.

The synthesis of polysubstituted indoles from 3-bromo-2-indolyl phosphates

A novel methodology for the synthesis of functionalised indoles based on the cross-coupling reactions of 3-bromo-2-indolyl phosphates is described. The preparation involves the conversion of easily available 2-oxindoles to 3,3-dibromo-2-oxindoles followed by the Perkow reaction affording 3-bromo-2-indolyl phosphates. Then bromine atom is substituted regioselectively by the Suzuki coupling reaction. We observed that aluminum chloride promoted the reaction of 3-substituted-2-indolyl phosphates with organozinc reagents furnishing 2,3-disubstituted indoles as final products. The overall diversity and efficiency of the methodology was demonstrated by the synthesis of bioactive molecule from easily available substances.

Intramolecular Halogen Atom Coordinated H Transfer via Ion-Neutral Complex in the Gas Phase Dissociation of Protonated Dichlorvos Derivatives

Intramolecular halogen atom coordinated H transfer reaction in the gas phase dissociation of protonated dichlorvos derivatives has been explored by electrospray ionization tandem mass spectrometry. Upon collisional activation, protonated dichlorvos underwent dissociation reaction via cleavage of the P-O bond to give reactive ion-neutral complex (INC) intermediate, [dimethoxylphosphinoylium + dichloroacetaldehyde]. Besides direct dissociation of the complex, intramolecular chlorine atom coordinated H transfer reaction within the complex takes place, leading to the formation of protonated dimethyl chlorophosphate. To investigate the fragmentation mechanism, deuterium-labeled experiments and several other halogen-substituted (Br and F) analogs of dichlorvos were prepared and evaluated, which display a similar intramolecular halogen transfer. Density functional theory (DFT)-based calculations were performed and the computational results also support the mechanism. Graphical Abstract ᅟ.

Functionalization of Silyldienol Ethers at the γ-Position via 2-Silyloxypentadienyl Cations

This report describes Brønsted acid catalyzed de novo synthesis of silyldienol ethers bearing tetrasubstituted double bonds via an intermediacy of 2-silyloxypentadienyl cations. The reactivity of these novel cationic intermediates could be modulated and harnessed toward direct nucleophilic additions regioselectively at the γ-position to produce highly functionalized silyldienol ethers with tunable control of the resulting double bond geometry.

Successive Cu/Pd transmetalation relay catalysis in stereoselective synthesis of tetraarylethenes

A new and efficient strategy for the synthesis of tetraaryl-substituted olefins with two cis furans based on a Cu/Pd catalyzed oxidative coupling reaction of cyclopropene with internal alkyne was developed. These novel tetraarylethenes were fully characterized and proved to be good AIE luminogens.

Regio- and stereoselective multisubstituted olefin synthesis via hydro/carboalumination of alkynes and subsequent iron-catalysed cross-coupling reaction with alkyl halides

A new synthetic route towards multisubstituted olefins was developed based on the direct cross coupling of alkenyl aluminium reagents, prepared by hydro- and carboalumination, with alkyl halides in the presence of an iron catalyst.