1,2-Palladasilacyclobutene: The Missing Link in the Pd-Catalyzed Annulation of Alkynes for the Silirene-to-Silole Transformation

The palladium-catalyzed annulation reaction of alkynes enables an attractive approach to siloles. Their access from silirenes and terminal alkynes proved rather general, involving reactive intermediates that have remained elusive to date. Starting from 1,2-bis(3-thienyl)silirene as a source of photochromic siloles, the mechanism of the annulation reaction has been revisited, and palladasilacyclobutenes resulting from the activation of the silirene could be isolated and thoroughly characterized (NMR, X-ray, and DFT). Their role as reactive intermediates and their fate in the course of the reaction were also studied in situ. In combination with in-depth DFT calculations, a clearer picture of the mechanism and the reactive key species is disclosed.

Nickel(0)-Catalyzed Asymmetric Ring Expansion Toward Enantioenriched Silicon-Stereogenic Benzosiloles

The development of a straightforward strategy to obtain enantioenriched silicon-stereogenic benzosiloles remains a challenging yet appealing synthesis venture due to their potential future application in chiral electronic and optoelectronic devices. In this context, all of the existing methods rely on Rh-catalyzed systems and are somewhat limited in scope. Herein, we disclose the first Ni⁰ -catalyzed ring expansion process that enables the preparation of benzosiloles possessing tetraorganosilicon stereocenters in excellent yields and enantioselectivities. The presented catalysis strategy is further applied to the asymmetric synthesis of silicon-stereogenic bis-silicon-bridged π-extended systems. Preliminary studies reveal that such compounds exhibit fluorescence emission, Cotton effects and circularly polarized luminescence (CPL) activity.

Me3SiSiMe2(O n Bu): a disilane reagent for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement

Herein, a readily available disilane Me₃SiSiMe₂(OⁿBu) has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement. This protocol enables the incorporation of a silylene into different starting materials, including acrylamides, alkene-tethered 2-(2-iodophenyl)-1H-indoles, and 2-iodobiaryls, via the cleavage of Si–Si, Si–C, and Si–O bonds, leading to the formation of spirobenzosiloles, fused benzosiloles, and π-conjugated dibenzosiloles in moderate to good yields. Preliminary mechanistic studies indicate that this transformation is realized by successive palladium-catalyzed bis-silylation and Brook- and retro-Brook-type rearrangement of silane-tethered silanols.

A readily available disilane Me₃SiSiMe₂(OⁿBu) as a silylene source has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement.

Synthesis of Polysubstituted Germoles and Benzogermoles Using a Substoichiometric Amount of Diisobutylaluminum Hydride

We developed a synthetic route to unsymmetrically polysubstituted germoles bearing different substituents from 1-hydrogermyl-4-silyl-1,3-enynes. The reaction proceeded with 0.5 equiv of diisobutylaluminum hydride. Various 2-silylgermoles including benzogermoles were obtained in good to excellent yields. 2-Germylbenzogermoles could be also successfully synthesized from 1-hydrogermyl-4-germyl-1,3-enynes under the same reaction conditions.

A Combined Computational and Experimental Study of Rh-Catalyzed C-H Silylation with Silacyclobutanes: Insights Leading to a More Efficient Catalyst System

The study of new C-H silylation reagents and reactions remains an important topic. We reported that under Rh catalysis, silacyclobutanes (SCBs) for the first time were able to react with C(sp²)-H and C(sp³)-H bonds, however the underlying reasons for such a new reactivity were not understood. Through this combined computational and experimental study on C-H silylation with SCBs, we not only depict a reaction pathway that fully accounts for the reactivity and all the experimental findings but also streamline a more efficient catalyst that significantly improves the reaction rates and yields. Our key findings include: (1) the active catalytic species is a [Rh]-H as opposed to the previously proposed [Rh]-Cl; (2) the [Rh]-H is generated via a reductive elimination/β-hydride (β-H) elimination sequence, as opposed to previously proposed endocyclic β-H elimination; (3) the regio- and enantio-determining steps are identified; (4) and of the same importance, the discretely synthesized [Rh]-H is shown to be a more efficient catalyst. This work suggests that the [Rh]-H/diphosphine system should find further applications in C-H silylations involving SCBs.

Gold-Catalyzed Synthesis of Small Rings

Three- and four-membered rings, widespread motifs in nature and medicinal chemistry, have fascinated chemists ever since their discovery. However, due to energetic considerations, small rings are often difficult to assemble. In this regard, homogeneous gold catalysis has emerged as a powerful tool to construct these highly strained carbocycles. This review aims to provide a comprehensive summary of all the major advances and discoveries made in the gold-catalyzed synthesis of cyclopropanes, cyclopropenes, cyclobutanes, cyclobutenes, and their corresponding heterocyclic or heterosubstituted analogs.

Rhodium-catalyzed intramolecular carbosilylation of alkynes via C(sp3)–Si bond cleavage

A Rh(i)-catalyzed intramolecular cis-carbosilylation of alkynes was achieved to afford silatricyclic compounds in good yields.

Synthesis of Benzosiloles by Intramolecular anti-Hydroarylation via ortho-C-H Activation of Aryloxyethynyl Silanes

Straightforward synthesis of benzosiloles was achieved by the invention of Pd/acid-catalyzed intramolecular anti-hydroarylation of aryloxyethynyl(aryl)silanes via ortho-C-H bond activation. The aryloxy group bound to the ethynyl carbon is the key factor for this transformation.

Broad scope gold(i)-catalysed polyenyne cyclisations for the formation of up to four carbon–carbon bonds

The polycyclisation of polyeneynes catalyzed by gold(i) has been extended for the first time to the simultaneous formation of up to four carbon–carbon bonds, leading to steroid-like molecules with high stereoselectivity in a single step with low catalyst loadings.

Gold-catalysed reactions of diynes

In this critical review the reactivity patterns observed with different types of diyne substrates in gold catalysis are discussed. Apart from the many examples from homogeneous catalysis, the few examples from heterogeneous gold catalysis are also included. With a proper arrangement of the two alkynes unique and exciting reactivity patterns like 1,3-carbonyl transpositions, carbene transfer reactions, cascade annulations, macrocyclisations or the formation of gold vinylidene intermediates are observed. These reactions are of interest for organic synthesis, for pharmaceutical and medicinal chemistry and for material science.

Recent developments in synthetic methods for benzo[b]heteroles

Benzo[b]heteroles containing heteroatoms other than nitrogen and oxygen have received considerable attention for their potential applications in materials science. This poses an increasing demand for efficient, selective, and broad-scope methods for their synthesis. This review article summarizes the recent developments in synthetic methods and approaches to access representative members of the benzoheterole family.

A one-pot multicomponent facile synthesis of dihydropyrimidin-2(1H)-thione derivatives using triphenylgermane as a catalyst and its binding pattern validation

A series of substituted dihydropyrimidin-2(1H)-thione derivatives (1–8) have been synthesized and docked against enzymes human topoisomerase II alpha (4FM9) and Helicobacter pylori urease (1E9Y) for binding mode validation.

Ruthenium Hydride Catalyzed Silylvinylation of Internal Alkynes Using Ethylene as an Additive

An efficient synthetic strategy for the regiospecific silylvinylation of internal alkynes is described. This transformation is catalyzed by RuHCl(CO)(SIMes)PPh3 and provides a net 5-exo-dig trans-silylvinylation of internal alkynes. Ethylene was used to decrease reaction times and displayed altered selectivity at increased pressure. Furthermore, alkyl-substituted alkynes were acceptable substrates at 80 psi of ethylene.

Synthesis of silafluorenes and silaindenes via silyl radicals from arylhydrosilanes: intramolecular cyclization and intermolecular annulation with alkynes

Effective synthetic methods, involving silyl radical intermediates and furnishing silafluorenes and silaindenes via direct Si–H and C–H cleavage in one step, have been developed.

Rhodium-catalyzed intramolecular alkynylsilylation of alkynes

Rhodium-catalyzed intramolecular alkynylsilylation of alkynes is described, including its enantioselective variant for the creation of a silicon stereogenic center.

DFT studies on the mechanism of palladium-catalyzed carbon–silicon cleavage for the synthesis of benzosilole derivatives

DFT calculations have been carried out to study the detailed mechanism of Pd-catalyzed intermolecular coupling reactions of 2-silylaryl bromides with alkynes via selective cleavage of C(sp³)–Si bonds.

Noninnocent counterion effect on the rearrangements of cationic intermediates in a gold(I)-catalyzed alkenylsilylation reaction

A mechanistic DFT study of the gold(I)-catalyzed alkenylsilylation reaction of a silyl-tethered 1,6-enyne system is reported. A novel pathway involving bistriflimide counterion-assisted rearrangements of carbocation and silyl cation intermediates corroborates the experimental observations. The results suggest the important role of the counterion in modulating the reactivity of cationic intermediates in gold catalysis.

Tandem Cycloisomerization/Suzuki Coupling of Arylethynyl MIDA Boronates

A tandem gold-catalyzed cycloisomerization/Suzuki cross coupling sequence involving arylethynyl-N-methyliminodiacetic acid boronates is described. Combining the mildness of homogeneous gold catalysis with the versatility of N-methyliminodiacetic acid (MIDA) boronates, this tandem two-step method enables the rapid assembly of various aryl-substituted heterocycles without having to isolate or purify any heterocyclic MIDA boronate intermediates. Another major advantage of this method is that a wide range of heterocycles bearing different aryl groups may be made from a single MIDA boronate alkyne precursor.

Modular synthesis of polybenzo[b]silole compounds for hole-blocking material in phosphorescent organic light emitting diodes

A diversity-oriented synthetic strategy allowed us to design a series of conjugated molecules containing multiple benzosilole units that can be utilized as efficient hole-blocking materials for phosphorescent organic light emitting diodes (OLEDs). Some of these compounds showed a performance surpassing that of the current standard, bathocuproine. The new compounds were easily synthesized in a modular fashion from a previously reported 3-stannyl benzosilole building unit. Studies on the properties of these compounds in solution and in the solid state indicate that they possess high electron affinity, high ionization potential, and form stable amorphous films that show high electron-drift mobility. The correlation between their molecular properties and the efficiency of the OLED device performance is also investigated.

Synthesis of benzo[b]siloles via KH-promoted cyclization of (2-alkynylphenyl)silanes

(2-Alkynylphenyl)silanes undergo intramolecular cyclization in the presence of an excess or a subequimolar amount of potassium hydride to give a variety of new 2-substituted benzosiloles in good to excellent yields. Some of these compounds showed a high fluorescence quantum yield both in solution and in the solid state, and they also showed reversible reduction in THF.