On the Pd-Catalyzed Vinylation of Aryl Halides with Tris(alkoxy)vinylsilanes in Water

Pd-Catalyzed Vinylation of Aryl Halides with Inexpensive Organosilicon Reagents Under Mild Conditions

Pd-catalyzed Hiyama vinylation reaction of non-activated aryl chlorides and bromides under mild conditions was developed. The use of efficient vinyl donors and electron-rich sterically hindered phosphine ligands was critical for the success of the reaction. The products of this transformation can be used for Am/Cm separation, an important challenge in nuclear fuel reprocessing. The substituent effect on Am/Cm separating selectivity was also achieved, which could contribute to the development of new chromatographic materials for the separation of Am and Cm.

Catalytic Organic Reactions in Water toward Sustainable Society

Traditional organic synthesis relies heavily on organic solvents for a multitude of tasks, including dissolving the components and facilitating chemical reactions, because many reagents and reactive species are incompatible or immiscible with water. Given that they are used in vast quantities as compared to reactants, solvents have been the focus of environmental concerns. Along with reducing the environmental impact of organic synthesis, the use of water as a reaction medium also benefits chemical processes by simplifying operations, allowing mild reaction conditions, and sometimes delivering unforeseen reactivities and selectivities. After the "watershed" in organic synthesis revealed the importance of water, the development of water-compatible catalysts has flourished, triggering a quantum leap in water-centered organic synthesis. Given that organic compounds are typically practically insoluble in water, simple extractive workup can readily separate a water-soluble homogeneous catalyst as an aqueous solution from a product that is soluble in organic solvents. In contrast, the use of heterogeneous catalysts facilitates catalyst recycling by allowing simple centrifugation and filtration methods to be used. This Review addresses advances over the past decade in catalytic reactions using water as a reaction medium.

Mechanistic studies on the Pd-catalyzed vinylation of aryl halides with vinylalkoxysilanes in water: the effect of the solvent and NaOH promoter

The mechanism of the Pd-catalyzed vinylation of aryl halides with vinylalkoxysilanes in water has been studied using different catalytic precursors. The NaOH promoter converts the initial vinylalkoxysilane into a highly reactive water-soluble vinylsilanolate species. Similarly, deuterium-labeling experiments have shown that, irrespective of the catalytic precursor used, vinylation occurs exclusively at the CH vinylic functionality via a Heck reaction and not at the C-Si bond via a Hiyama cross-coupling. The involvement of a Heck mechanism is interpreted in terms of the reduced nucleophilicity of the base in water, which disfavors the transmetalation step. The Heck product (β-silylvinylarene) undergoes partial desilylation, with formation of a vinylarene, by three different routes: (a) hydrolytic desilylation by the aqueous solvent (only at high temperature); (b) transmetalation of the silyl olefin on the PdH Heck intermediate followed by reductive elimination of vinylarene; (c) reinsertion of the silyl olefin into the PdH bond of the Heck intermediate followed by β-Si syn-elimination. Both the Hiyama and Heck catalytic cycles and desilylation mechanisms b and c have been computationally evaluated for the [Pd(en)Cl2] precursor in water as solvent. The calculated Gibbs energy barriers support the reinsertion route proposed on the basis of the experimental results.

Copper-mediated transformation of organosilanes to nitriles with DMF and ammonium iodide

Cyanation of aryl-, diaryldimethyl-, and styrylsilanes was developed for the first time under copper-mediated oxidative conditions using ammonium iodide and DMF as the combined source of nitrogen and carbon atom of the introduced cyano unit, respectively. The reaction was observed to proceed in a two-step process: initial conversion of organosilanes to their iodo intermediates and then cyanation. This method has a broad substrate scope with high functional group tolerance.

Palladium-catalysed cross-coupling of organosilicon reagents

The palladium catalysed cross-coupling of organosilicon reagents with organo halides and pseudo-halides has developed over the past 30 years into an efficient and attractive carbon-carbon bond forming strategy. Extensive research within this field to expand and diversify on the scope of the organosilicon coupling reaction will continue to promote its use in the synthesis of biologically and pharmaceutically important organic molecules. The recent advances made within this area are explored in this critical review (199 references).

Synthesis of alpha-arylated allylsilanes through palladium-catalyzed gamma-selective allyl-aryl coupling

A palladium-catalyzed gamma-selective allyl-aryl coupling between gamma-silylated allylic esters and arylboronic acids produced alpha-arylated allylsilanes with E-alkene geometry. The reaction tolerated various functional groups in both the arylboronic acids and the allylic esters and afforded functionalized allylsilanes. The reaction of optically active allylic esters took place with excellent alpha-to-gamma chirality transfer with syn stereochemistry to give chiral allylsilanes.

Synthetic and mechanistic studies on Pd(0)-catalyzed diamination of conjugated dienes

Various dienes and a triene can be regioselectively diaminated at the internal double bond with good yields and high diastereoselectivity using di-tert-butyldiaziridinone (5) as the nitrogen source and Pd(PPh(3))(4) (1-10 mol %) as the catalyst. Kinetic studies with (1)H NMR spectroscopy show that the diamination is first-order in total Pd catalyst and inverse first-order in PPh(3). For reactive dienes, such as 1-methoxybutadiene (6g) and alkyl 1,3-butadienes (6a, 6j), the diamination is first-order in di-tert-butyldiaziridinone (5) and zero-order in the olefin. For olefins with relatively low reactivity, such as (E)-1-phenylbutadiene (6b) and (3E,5E)-1,3,5-decatriene (6i), similar diamination rates were observed when 3.5 equiv of olefins were used. Pd(PPh(3))(2) is likely to be the active species for the insertion of Pd(0) into the N-N bond of di-tert-butyldiaziridinone (5) to form a four-membered Pd(II) complex (A), which can be detected by NMR spectroscopy. The olefin complex (B), formed from intermediate A via ligand exchange between the olefin substrate and the PPh(3), undergoes migratory insertion and reductive elimination to give the diamination product and regenerate the Pd(0) catalyst.