Regioselective hydrosilylations of propiolate esters with tris(trimethylsilyl)silane

Hydrosulfonylation of Alkynes for Stereodivergent Synthesis of Vinyl Sulfones: Synthetic Strategy and Mechanistic Insights

Direct synthesis of thermodynamically less favorable (Z)-vinyl sulfones presents a notable challenge in organic synthesis. In addition, the development of a stereodivergent synthesis for (E)- and (Z)-vinyl sulfones is crucial but remains elusive. In this study, we present a hydrosulfonylation of aryl-substituted alkynes, achieving a stereodivergent synthesis of (E)- and (Z)-vinyl sulfones by leveraging both thermodynamic and kinetic controls. Notably, the synthesis of challenging (Z)-vinyl sulfones was achieved through a kinetically controlled process without the need for a catalyst. To synthesize (E)-vinyl sulfones, unconventional visible light-mediated isomerization was employed as a means of facilitating the transition to the thermodynamically favored form. The present study encompasses a comprehensive experimental and computational investigation, which provides valuable insights into the reaction mechanism. This investigation reveals two plausible isomerization pathways: a novel double spin-flip mechanism and a hydrogen atom transfer process in the presence of eosin Y. This study not only advances our understanding of isomerization mechanisms beyond conventional energy-transfer routes but also offers a robust and switchable strategy for synthesizing (E)- and (Z)-vinyl sulfones, thereby providing a versatile avenue for the creation of valuable compounds in the fields of organic synthesis and medicinal chemistry.

Intermolecular 1,3-Dipolar Cycloaddition Reaction of N-Carbamoyl Nitrones Generated by N-Selective Carbamoylation of Oximes with Isocyanates

N-Selective carbamoylation reaction of oximes with isocyanates generates nitrones, which undergo 1,3-dipolar cycloaddition with various dipolarophiles to afford diverse isoxazolidines. Notably, combinations of highly electron-rich oxime and highly electron-deficient dipolarophile exhibited high reactivity, with product yields of up to 94 %. The substituent on the isoxazolidine-nitrogen atom could be successfully removed without loss of the cyclic structure. Computational studies have also elucidated the mechanism of the reaction and origin of stereoselectivity.

Visible Light-Induced Diastereoselective Construction of Trifluoromethylated Cyclobutane Scaffolds through [2+2]-Photocycloaddition and Water-Assisted Hydrodebromination

A visible light-induced diastereoselective synthesis of trifluoromethylated cyclobutane derivatives is described, consisting of [2+2]-photocycloaddition and water-assisted hydrodebromination by one pot. Quinolinones, isoquinolinones, and coumarins are able to participate in this one-pot process with 1-bromo-1-trifluoromethylethene. In addition, stereodefined trisubstituted trifluoromethylated cyclobutane alcohols, carboxylic acids, and amines can be obtained in a straightforward manner through the ring opening of lactone or lactam without the loss of original high diastereoselectivity given by the water-tristrimethylsilylsilane coordination. The antineoplastic bioactivities of those compounds are also well studied, which exhibit great antineoplastic potential comparable to cisplatin. In the proposed mechanism, thioxanthone (TX) serves as a dual catalyst and a radical chain pathway may be involved in the hydrodebromination process.

C(sp3)-C(sp3) coupling of non-activated alkyl-iodides with electron-deficient alkenes via visible-light/silane-mediated alkyl-radical formation

Here, we present a remarkably mild and general initiation protocol for alkyl-radical generation from non-activated alkyl-iodides. An interaction between a silane and an alkyl iodide is excited by irradiation with visible light to trigger carbon-iodide bond homolysis and form the alkyl radical. We show how this method can be developed into an operationally simple and general Giese addition reaction that can tolerate a range of sensitive functionalities not normally explored in established approaches to this strategically important transformation. The new method requires no photocatalyst or other additives and uses only commerical tris(trimethylsilyl)silane and visible light to effectively combine a broad range of alkyl halides with activated alkenes to form C(sp3)-C(sp3) bonds embedded within complex frameworks.

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.

Copper(II)-catalyzed silylation of activated alkynes in water: diastereodivergent access to E- or Z-β-silyl-α,β-unsaturated carbonyl and carboxyl compounds

Copper(II)-catalyzed silylation of substituted alkynylcarbonyl compounds was investigated. Through the activation of Me2 PhSiBpin in water at room temperature and open atmosphere, vinylsilanes conjugated to carbonyl groups are synthesized in high yield. A surprising diastereodivergent access to olefin geometry was discovered using a silyl conjugate addition strategy: aldehydes and ketones were Z selective while esters and amides were exclusively transformed into the E products.

One-step chemoselective conversion of tetrahydropyranyl ethers to silyl-protected alcohols

A novel chemoselective one-pot transformation of acetals to silyl ethers is reported. Free hydroxyls, double bonds and triple bonds are unaffected in optimal reaction conditions. This practical, inexpensive protocol allows the selective replacement of acetal-forming protecting groups with silyl groups in a single step under mild conditions.

Room temperature hydrosilylation of silicon nanocrystals with bifunctional terminal alkenes

H-terminated Si nanocrystals undergo room temperature hydrosilylation with bifunctional alkenes with distal polar moieties-ethyl ester, methyl ester, or carboxylic acids-without the aid of light or added catalyst. The passivated Si nanocrystals exhibit bright photoluminescence (PL) and disperse in polar solvents, including water. We propose a reaction mechanism in which ester or carboxylic acid groups facilitate direct nucleophilic attack of the highly curved Si surface of the nanocrystals by the alkene.

Si(111) surface modified with alpha,beta-unsaturated carboxyl groups studied by MIR-FTIR

A Si(111) surface modified with alpha,beta-unsaturated carboxyl groups was fabricated using activated alkynes such as propiolic acid and propiolic acid methyl ester via hydrosilylation reaction. The obtained coverage of carboxyl groups was roughly estimated to be 55-60% in both cases from the Si-2p and C-1s X-ray photoelectron specroscopy (XPS) peak intensities. The detailed surface structures were investigated by multiple internal reflection Fourier transform infrared (MIR-FTIR) measurement. It was revealed that this reaction was promoted by visible light irradiation at room temperature. The Si surface modified with functional groups prepared under such a moderate condition is adaptable to functional devices which are easily damaged under UV irradiation or high temperature conditions.

Vinyl Tris(trimethylsilyl)silanes: Substrates for Hiyama Coupling

The oxidative treatment of vinyl tris(trimethylsilyl)silanes with hydrogen peroxide in aqueous sodium hydroxide in tetrahydrofuran generates reactive silanol or siloxane species that undergo Pd-catalyzed cross-couplings with aryl, heterocyclic and alkenyl halides in the presence of Pd(PPh(3))(4) and tetrabutylammonium fluoride. Hydrogen peroxide and base are necessary for the coupling to occur while activation of the silanes with fluoride is not required. The conjugated and unconjugated tris(trimethylsilyl)silanes serve as good cross-coupling substrates. The (E)-silanes undergo coupling with retention of stereochemistry while coupling of (Z)-silanes occurred with lower stereoselectivity to produce an E/Z mixture of products.

Trans- and cis-selective Lewis acid catalyzed hydrogermylation of alkynes

[reactions: see text] The first examples of Lewis acid catalyzed hydrogermylation of alkynes have been demonstrated. It was found that this method has much higher functional group compatibility compared to the known Lewis acid catalyzed hydrosilylation and hydrostannation reactions. Remarkably, the stereochemical outcome of this hydrogermylation reaction depends on the nature of the alkyne used: proceeding via a trans-addition pathway with simple alkynes and cis-addition with propiolates. Mechanistic studies strongly support the proposed rationale on the origins of cis-selectivity in the hydrogermylation of activated alkynes.

DyI2 initiated mild and highly selective silyl radical-catalyzed cyclotrimerization of terminal alkynes and polymerization of MMA

An efficient method for the formation of SiCl3 radicals by the reaction of abundant and cheaper chlorosilanes with DyI2 has been established, not only demonstrating new distinctive reactivities of solvated DyI2 but also suggesting that the presence of lanthanide ions can improve the selectivity of some silyl radical-catalyzed reactions.

Surface structures, photovoltages, and stability of n-Si(111) electrodes surface modified with metal nanodots and various organic groups

The surface structures, photovoltages, and stability of n-Si(111) electrodes surface-modified with Pt nanodots and organic groups were studied in an I-/I3- redox electrolyte, using alkyls of varied chain length and those having a double bond and ester at the terminal as the organic groups. The n-Si was first modified with the organic groups, and then Pt was electrodeposited on it. Linear sweep voltammetry revealed that, for the modification with alkyls, the overvoltage for the Pt deposition became significantly larger with increasing alkyl chain length, though this does not necessarily hold for the modification with alkyls having a double bond and ester. Scanning electron microscopic inspection showed that the Pt particle density decreased and the particle size increased, with increasing alkyl chain length. The photovoltaic characteristics and stability for the n-Si electrodes modified with the organic groups were much improved by the Pt nanodot coating, though they became somewhat inferior with increasing alkyl chain length. On the basis of these results, it is concluded that surface alkylation at high coverage together with coating with small Pt nanodots gives efficient and stable n-Si electrodes.