Alkenyl- and aryl[2-(hydroxymethyl)phenyl]dimethylsilanes: an entry to tetraorganosilicon reagents for the silicon-based cross-coupling reaction

Alkenyl- and aryl[2-(hydroxymethyl)phenyl]dimethylsilanes, highly stable tetraorganosilicon reagents, are found to react with aryl and alkenyl iodides in the presence of a palladium catalyst and K2CO3 as a base, significantly milder conditions compared with those ever reported for the silicon-based cross-coupling reactions. The reaction tolerates a wide range of functional groups, including silyl protectors, and allows a gram-scale synthesis to recover and reuse the silicon residue.     

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).     

Intramolecular syn and anti hydrosilylation and silicon-assisted cross-coupling: highly regio- and stereoselective synthesis of trisubstituted allylic alcohols

[reaction: see text] The geometrical isomers of 6-ethylidenedioxadisilacyclohexane were prepared by intramolecular hydrosilylation of an unsymmetrical disiloxane by the use of Pt (syn) and Ru (anti) catalysts. This new class organosilicon reagents underwent cross-coupling reactions with a range of aryl iodides to afford (E)- and (Z)-trisubstituted allylic alcohols in a highly stereospecific fashion.     

Reaction of (bromodifluoromethyl)phenyldimethylsilane with organometallic reagents

A new fluorine-containing organosilicon compound, (bromodifluoromethyl)-phenyldimethylsilane (II), was synthesized by the N-bromosuccinimide (NBS) bromination of difluoromethyl)phenyldimethylsilane (I), which was prepared from phenyldimethylsilyllithium and chlorodifluoromethane. Compound II reacted with dimethyl sulfoxide to give dimethyl sulfide and phenyldimethylfluorosilane in quantitative yield. The reaction of II with nucleophiles, such as sodium ethoxide, Grignard or lithium reagents, afforded products arising from cleavage of the carbonsilicon bond. In contrast, the reaction of II with Grignard reagents in the presence of appropriate catalysts (Group VIII transition metal salts or complexes) afforded the homo-coupling product of II, 1,2-bis-(phenyldimethylsilyl)-1,1,2,2-tetrafluoroethane (IV), in excellent yield. The silver(I) salt-catalyzed reaction of II with ethylmagnesium bromide gave the cross-coupling product, (1,1-difluoropropyl)phenyldimethylsilane (V) as well as III and IV. When cuprous bromide was employed as catalyst, the reaction of II with ethylmagnesium bromide afforded 1-phenyldimethylsilyl-1-propene (VI) and 3-phenyldimethylsilyl-2-pentene (VII) as main products.     

Fluoride-promoted cross-coupling reactions of alkenylsilanols. Elucidation of the mechanism through spectroscopic and kinetic analysis

The mechanism of the palladium-catalyzed cross-coupling reaction of (E)-dimethyl-(1-heptenyl)silanol ((E)-1) and of (E)-diisopropyl-(1-heptenyl)silanol ((E)-2) with 2-iodothiophene has been investigated through spectroscopic and kinetic analysis. A common intermediate in cross-coupling reactions of several types of organosilicon precursors has been identified as a hydrogen-bonded complex between tetrabutylammonium fluoride (TBAF) and a silanol. The order in each component has been determined by plotting the initial rates of the cross-coupling reaction at varying concentrations. These data provide a mechanistic picture that involves a fast and irreversible oxidative insertion of palladium into the aryl iodide and a subsequent turnover-limiting transmetalation step achieved through a fluoride-activated disiloxane derived from the particular silanol employed. The inverse order dependence of TBAF at high concentration is consistent with a pathway that proceeds through a hydrogen-bonded complex which is the lowest energy silicon species in solution.     

Unification of anion relay chemistry with the Takeda and Hiyama cross-coupling reactions: identification of an effective silicon-based transfer agent

The unification of Anion Relay Chemistry (ARC) with the Takeda and Hiyama palladium-mediated cross-coupling processes to provide aryl-aryl, alkenyl-aryl, and alkenyl-alkenyl coupled products by exploiting a common silicon-based transfer agent has been achieved. These results provide a practical solution for intermolecular cross-coupling of organolithium reagents without the problematic lithium-halogen exchange and/or undesired homocoupling that has kept organolithium cross-couplings from achieving the same level of utility asother palladium-mediated methods (e.g., Suzuki organoboron, Negishi organozinc, Stille organotin, Kumada organomagnesium, etc.).     

Cross-coupling reactions of organosilicon compounds: new concepts and recent advances

This review highlights the rapid evolution of the newly-developed class of palladium-catalyzed cross-coupling reactions of organosilicon compounds. A myriad of heteroatom-containing silicon moieties (silyl hydrides, siletanes, silanols, silyl ethers, orthosiliconates, di- and polysiloxanes and pyridylsilanes) undergo mild and stereospecific cross-coupling. The diversity of methods for introduction of silicon groups into organic molecules and the range of organic electrophiles that can be used are emphasized.     

Silicon‐Based Cross‐Coupling Reactions in the Total Synthesis of Natural Products

Unlike other variants of transition‐metal‐catalyzed cross‐coupling reactions, those based on organosilicon donors have not been used extensively in natural product synthesis. However, recent advances such as: 1) the development of mild reaction conditions, 2) the expansion of substrate scope, 3) the development of methods to stereoselectively and efficiently introduce the silicon‐containing moiety, 4) the development of a large number of sequential processes, and 5) the advent of bifunctional bis(silyl) linchpin reagents, signify the coming of age of silicon‐based cross‐coupling reactions. The following case studies illustrate how silicon‐based cross‐coupling reactions play a strategic role in constructing carbon–carbon bonds in selected target molecules.     

Thermochemistry of thermal plasma chemical reactions. Part II. A survey of synthesis routes for silicon nitride production

Feasibility routes for thermal plasma production of silicon nitride powders are explored. First, a collation of the various proposed systems from the extant literature is examined. Reactant systems investigated include free silicon, silicon monoxide, silicon dioxide, silicon tetrachloride, silane, and other organosilicon precursors, along with various nitriding and reducing species. The reaction yields of these systems are brought to a common denominator by thermodynamic analysis and a first-step introduction of nucleation kinetics including comparisons against published experiments and the authors' own research. In particular, it is observed that the formation of liquid-phase free silicon in the neighborhood of 2500 K is quite detrimental to silicon nitride yield, and furthermore, a high supersaturation of silicon should always be avoided.     

The role of Cul in the siloxane-mediated Pd-catalyzed cross-coupling reactions of aryl iodides with aryl lithium reagents

Experiments indicate that a catalytic amount of Cul plays an important role in the siloxane-mediated Pd-catalyzed cross-coupling reactions with the direct use of organolithium reagents.Addition of organolithium to the siloxane transfer agent generates an organosilicon intermediate.DFT calculations indicate that Cul initially accelerates the Si-Pd(Ⅱ) transmetalation of the organosilicon intermediate by the formation of CuI₂^-.Subsequently,CuI₂^-works as a shuttle between the Si-Cu(Ⅰ) and Cu(Ⅰ)-Pd(Ⅱ)transmetalation processes.     

The effect of substituents at silicon on the cross-metathesis of trisubstituted vinylsilanes with olefins

Efficient cross-metathesis of vinylsilanes, carrying a large spectrum of different substituents at silicon, with various olefins in the presence of the first and second generation Grubbs catalyst and Hoveyda–Grubbs catalyst is described. On the basis of the results of equimolar reactions of vinylsilanes with ruthenium alkylidene complexes and experiments with deuterium-labelled reagents, a general, metallacarbene mechanism for the cross-metathesis of trisubstituted vinylsilanes with olefins has been suggested. Reaction was proved to be a valuable method for synthesis of unsaturated organosilicon derivatives.     

Stereocontrolled total syntheses of isodomoic acids G and H via a unified strategy

Marine neuroexcitatory compounds isodomoic acids G and H were efficiently synthesized from a common intermediate using a silicon-based cross-coupling reaction. Dividing each target compound into the core fragment and the side-chain fragment enabled the synthesis to be convergent. The trans-2,3-disubstituted pyrrolidine core fragment was accessed through a diastereoselective rhodium-catalyzed carbonylative silylcarbocyclization reaction of a vinylglycine-derived 1,6-enyne. A stereochemically divergent desilylative iodination reaction was developed to convert the cyclization product to both E- and Z-alkenyl iodides, which would eventually lead to isodomoic acid G and isodomoic acid H, respectively. The late-stage alkenyl-alkenyl silicon-based cross-coupling reaction uniting the core alkenyl iodides and the side-chain alkenylsilanol was achieved under mild conditions. Finally, two mild deprotections afforded the target molecules.     

Preparation of 2,3-disubstituted indoles by sequential Larock heteroannulation and silicon-based cross-coupling reactions

A simple and convergent synthesis of 2,3-disubstituted indoles has been developed using a sequential Larock indole synthesis and silicon-based, cross-coupling reaction. Substituted 2-iodoanilines reacted with an alkynyldimethylsilyl tert-butyl ether to afford indole-2-silanols under the Larock heteroannulation conditions after hydrolysis. The corresponding sodium 2-indolylsilanolate salts successfully engaged in cross-coupling with aryl bromides and chlorides to afford multi-substituted indoles. The development of an alkynyldimethylsilyl tert-butyl ether as a masked silanol equivalent enabled a smooth heteroannulation process and the identification of a suitable catalyst/ligand combination provided for a facile cross-coupling reaction.     

硅杂四元环化合物的合成和反应

硅杂四元环化合物在有机硅化学中是一类非常重要的小分子环系化合物, 广泛应用于有机化学、金属有机化学以及材料化学. 环上只含有一个硅原子的硅杂环丁烷可以通过γ-卤代丙基硅烷的Grignard反应、Si＝C键与烯烃的 [2＋2]环加成反应以及硅杂环丙烷的扩环反应合成, 环上只含有一个硅原子的硅杂环丁烯可以通过格氏试剂或锂试剂参与的Si—C键的关环反应、硅杂环丁烷的转化反应、硅卡宾对C—H键的插入反应、Si＝C键与炔烃的[2＋2]环加成反应以及二炔基硅烷的分子内成环反应等途径合成. 硅杂环丁烷和硅杂环丁烯由于存在环张力和具有一定的Lewis酸性, 能够通过扩环反应生成五元和六元含硅杂环化合物, 也能够通过开环反应生成不同结构的有机硅分子和聚合物, 抑或实现有机反应在温和条件下的转化.     

Synthesis and cross-coupling reaction of alkenyl[(2-hydroxymethyl)phenyl]dimethylsilanes

Highly stable alkenyl[2-(hydroxymethyl)phenyl]dimethylsilanes are prepared by stereo- and regioselective hydrosilylation of alkynes catalyzed either by a platinum or ruthenium catalyst using protected [2-(hydroxymethyl)phenyl]dimethylsilanes. Cyclic silyl ether, 1,1-dimethyl-2-oxa-1-silaindan, also serves as a starting material for the alkenylsilanes by the ring-opening reaction with alkenyl Grignard reagents. The resulting alkenylsilanes undergo cross-coupling reaction with various aryl and alkenyl iodides under reaction conditions employing K₂CO₃ as a base at 35–50 °C in highly regio- and stereospecific manners. The reaction tolerates a diverse range of functional groups including silyl protections. The silicon residue is readily recovered and reused on a gram-scale synthesis. Intramolecular coordination of a proximal hydroxyl group is considered to efficiently form pentacoordinate silicates having a transferable group possibly at an axial position and, thus, responsible for the cross-coupling reaction under conditions significantly milder than those reported for the silicon-based reactions.     

Sequential silylcarbocyclization/silicon-based cross-coupling reactions

A sequential rhodium-catalyzed silylcarbocyclization of enynes parlayed with a palladium-catalyzed, silicon-based cross-coupling reaction has been developed for the synthesis of highly substituted cyclopentanes. 1,6-Enynes reacted with benzyldimethylsilane in the presence of rhodium catalysts to afford five-membered rings bearing a (Z)-alkylidenylbenzylsilyl group. A variety of substitution patterns and heteroatom substituents were compatible. The silylcarbocyclization in which an unsaturated ester participated was also achieved. The resulting alkylidenylsilanes underwent palladium-catalyzed cross-coupling using tetra-n-butylammonium fluoride. This cross-coupling reaction displayed a broad substrate scope. A wide variety of substitution patterns, electronic properties, and heteroatoms were compatible. All of the cross-coupling reactions proceeded in high yields under very mild conditions and with complete retention of double bond configuration, resulting in densely functionalized 3-(Z)-benzylidenecyclopentanes and heterocycles.     

Cross-coupling of non-activated chloroalkanes with aryl Grignard reagents in the presence of iron/N-heterocyclic carbene catalysts

An efficient and high-yielding cross-coupling reaction of various primary, secondary, and tertiary alkyl chlorides with aryl Grignard reagents was achieved by using catalytic amounts of N-heterocyclic carbene ligands and iron salts. This reaction is a simple and efficient arylation method having applicability to a wide range of industrially abundant chloroalkanes, including polychloroalkanes, which are challenging substrates under conventional cross-coupling conditions.     

Thiol-Specific Silicon-Containing Conjugating Reagent: β-Silyl Alkynyl Carbonyl Compounds

Site-specific modification of thiol-containing biomolecules has been recognized as a versatile and powerful strategy for probing our biological systems and discovering novel therapeutics. The addition of lipophilic silicon moiety opens up new avenues for multi-disciplinary research with broad applications in both the medicinal and material sciences. However, adhering to the strict biocompatibility requirements, and achieving the introduction of labile silicon handle and high chemo-selectivity have been formidable. In this paper, we report silicon-based conjugating reagents including β-trialkylsilyl and silyl ether-tethered alkynones that selectively react with thiols under physiological conditions. The pH-neutral, metal-free and additive-free reaction yields stable products with broad substrate compatibility and full retention of silicon handles in most cases. Besides simple aliphatic and aromatic thiols, this approach is applicable in the labeling of thiols present in proteins, sugars and payloads, thereby expanding the toolbox of thiol conjugation.     

Nickel(0)-catalyzed diastereoselective three-component coupling of 1,3-dienes, aldehydes, and organometallic reagents: influence of organometallic reagents on diastereoselectivity

A nickel-catalyzed diastereoselective alkylative three-component coupling of 1,3-diene and aldehyde with organoboron or organosilicon reagents has been realized. The diastereoselectivity was dramatically changed depending on the class of organometallic reagents. The reaction using ArB(OH)₂ in the presence of PPh₃ afforded 1,3-syn-substituted 4-penten-1-ol derivative as a single diastereomer. On the other hand, the coupling reaction with tetraorganosilicon reagent using NHC as a ligand under similar conditions exclusively produced the corresponding 1,3-anti isomer.     

Selective organic synthesis through generation and reactivity control of hyper‐coordinate metal species

This paper is a review of my 40 years of research at Kyoto, Sagamihara, and Yokohama, all based on the generation of hyper‐coordinate metal species such as ate complexes and pentacoordinate silicates. The topics are: (i) carbenoid reagents for carbon–carbon bond‐forming reactions, (ii) nucleophilic substitution at acetal carbons using aluminate reagents, (iii) preparation of magnesium enolates and its reaction with nitriles, (iv) Cr(II) reagents for reduction of organic halides and highly selective carbon–carbon bond formation, (v) organic synthesis with organosilion reagents/fluoride ions, (vi) cross‐coupling reaction of organosilicon compounds, and (vii) silicon‐based conjugate addition to α,β‐unsaturated carbonyl acceptors. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 337–350; 2008: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20162