Search

This paper provides the first report of the intramolecular [2+2] cycloaddition of vinylsilane. The [2+2] cycloaddition of allenes is a useful reaction that can synthesize cyclobutanes. However, no previous works have attempted to control the regioselectivity between the two double bonds of allenes only by changing the reaction conditions, although there have been some reports of the regioselective [2+2] cycloaddition of allenes by changing the substrate. In this study, we have succeeded in controlling intramolecular [2+2] cycloaddition reactions at the proximal and distal positions of allenes simply by changing the reaction conditions. We found that the atomic radius of silicon is very important for perfect control of the reaction's sites. The structures of all key compounds were determined by the crystal sponge method which could identify the structures of liquid compounds. [ABSTRACT FROM AUTHOR]

Vinylsilanes and vinylboronates are common building blocks for organic synthesis, but direct functionalization of these species without the participation of either the C=C or C−Si/B bonds is rare. Herein, we report a metal‐free allylic C−H amination reaction of these vinylmetalloid species that installs a new C−N bond without competing transmetallation or alkene addition. In this transformation, the silicon or boron substituent inverts the usual regioselectivity, directing amination to the site distal to that group. Subsequent cross‐coupling or demetallation allows access to complementary regioisomeric products. Density Functional Theory computations revealed that the observed regioselectivity is due to a subtle combination of electronic and counterintuitive steric factors that favor initial attack of selenium at the silicon‐bearing carbon atom. [ABSTRACT FROM AUTHOR]

A copper‐catalyzed asymmetric hydroallylation of readily available vinylsilanes with allylic phosphates in the presence of hydrosilane was developed. These transformations can be performed under mild reaction conditions and provide the useful chiral organosilanes with good to excellent level of enantiocontrol. [ABSTRACT FROM AUTHOR]

The stereoselective synthesis of optically active cyclopropylsilanes from various allyl‐ and vinylsilanes with functionalized diazoesters was achieved in excellent yields (up to 99 %) and diastereo‐ (up to >99 : 1 d.r.) and enantioselectivities (up to 99 % ee) in the presence of Ru(II)‐Pheox catalysts. Among a series of Ru(II)‐Pheox catalysts, p‐MeO−Ru(II)‐Pheox was determined to be the best catalyst for cyclopropanation reactions of diazoesters with various allylsilanes. Also, methyl(diazoacetoxy)acetate afforded in significantly enhanced yields, diastereoselectivities, and enantioselectivities. The cyclopropanation reactions with vinylsilanes with methyl (diazoacetoxy)acetate proceeded with excellent diastereoselectivities (>99 : 1 d.r.). Moreover, cyclopropylsilane derivatives could be successfully transformed into beneficial building blocks for the synthesis of bioactive compounds, including an anti‐HIV drug and Imatinib‐7. [ABSTRACT FROM AUTHOR]

An in‐depth theoretical study has been performed to investigate the mechanism of alkene dehydrogenative silylation catalyzed by the bis(imino)pyridine cobalt methyl complex (MesPDI)Co(CH3) on the singlet, triplet and open‐shell singlet potential energy surfaces as well as the corresponding minimum energy crossing points. The formation of active catalyst [(MesPDI)Co(CH3)+HSiR3→(MesPDI)Co−[Si]+CH4] follows an open‐shell singlet potential energy surface, while the active catalyst has a triplet ground state. For 1‐butene as substrate, the formation of E/Z‐allylsilanes follows the singlet surface; and the E‐allylsilane is more favored than the Z‐allylsilane kinetically, and the expected ratio agrees with the experiment. For bulky 4,4‐dimethyl‐1‐pentene as substrate, the selectivity of allylsilane and vinylsilane is thermodynamically determined and this is supported by the need of low silane/olefin ratio (1/4) in experiment. [ABSTRACT FROM AUTHOR]

Abstract: The strategic carbon‐to‐silicon substitution at a stereogenic center can produce chiral silanes with significantly improved properties relative to their carbon congeners. We herein report an unprecedented cobalt‐catalyzed asymmetric hydrosilylation of unsymmetric alkynes with dihydrosilanes that furnishes silicon‐stereogenic vinylhydrosilanes with high regio‐ and enantioselectivity. The absolute configurations of the products were determined by chiroptical methods in combination with DFT calculations. The synthetic versatility of the vinylhydrosilanes as chiral building blocks was further demonstrated by asymmetric Si−H insertion and catalytic hydroboration reactions. [ABSTRACT FROM AUTHOR]

Abstract: The air‐stable unsymmetrical disilane Me3Si−SiMe2[oCON(iPr)2C6H4] has been developed for bis‐silylation of alkynes. This reagent tolerates a range of functional groups, providing Z‐vinyl disilanes in high yields. It is proposed that the phenyl‐ring‐tethered amide group directs oxidative addition of Pd0 into the Si−Si bond, which might facilitate formation of a six‐membered Pd cycle, generating products with good to excellent regioselectivity. [ABSTRACT FROM AUTHOR]

A cobalt-catalyzed Z-selective hydrosilylation of alkynes has been developed relying on catalysts generated from bench-stable Co(OAc)2 and pyridine-2,6-diimine (PDI) ligands. A variety of functionalized aromatic and aliphatic alkynes undergo this transformation, yielding Z-vinylsilanes in high yields with excellent selectivities ( Z/ E ratio ranges from 90:10 to >99:1). The addition of a catalytic amount of phenol effectively suppressed the Z/ E-isomerization of the Z-vinylsilanes that formed under catalytic conditions. [ABSTRACT FROM AUTHOR]

A catalytic intramolecular silapalladation of alkynes affords, in good yields and stereoselectively, syn-disilylated heterocycles of different chemical structure and size. When applied to silylethers, this reaction leads to vinylic silanols that undergo a rhodium-catalyzed addition to activated olefins, providing the oxa-Heck or oxa-Michael products, depending on the reaction conditions. [ABSTRACT FROM AUTHOR]

A pyridinebis(oxazoline) cobalt complex is a very efficient precatalyst for the hydrosilylation of terminal alkynes with Ph2SiH2, providing α-vinylsilanes with high (Markovnikov) regioselectivity and broad functional-group tolerance. The vinylsilane products can be further converted into geminal borosilanes through Markovnikov hydroboration with pinacolborane and a bis(imino)pyridine cobalt catalyst. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) was used to investigate computationally cobalt(I)-catalyzed of vinylsilanes and alkyl aldehydes to give ketones. Calculation indicated that cobalt(I)-catalyzed had eight possible reaction pathways. In the cobalt-hydride complexes IM2a and IM2b, the hydrogen migration occurred prior to the carbon-carbon bond-forming reaction. In the complexes IM3a1 and IM3b1, the carbonyl elimination reaction occurred prior to the direct reductive elimination reaction. In the cobalt-carbonyl complexes IM4a and IM4b, the carbonyl was much easier to achieve than the reaction. The dominant reaction pathway was the reaction channel IM1a → TS1a → IM2a → TS2a1 → IM3a1 → TS4a → IM4a → TS5a → IM5a → TS6a → IM6a, and the reductive elimination reaction was the rate-determining step for this channel, so the dominant product predicted theoretically was the linear ketone. Furthermore, the solvation effect was remarkable, and it decreased generally the free energies of the species. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Recently we reported a second-generation ligand, bis(3,5-di- tert -butylphenyl)( tert -butyl)phosphine, for the preparation of allyl silanes using the silyl-Heck reaction. We now show that this new ligand also provides superior reactivity in the preparation of vinylsilanes from styrene derivatives. For the first time, this new ligand provides exceptionally high yields of trialkylvinylsilanes using a widely available palladium pre-catalyst, Pd 2 (dba) 3 . Finally, we demonstrate that this new catalyst system is able to form more highly decorated all carbon substituted vinylsilanes that have been shown to possess superior reactivity in oxidation and cross coupling reactions.