Addition Of Silyl Research Articles

Indium(III)-catalyzed intramolecular addition of silyl enolates to alkynes

In the presence of water and a catalytic amount of InBr3, intramolecular trans-addition of silyl enolates derived from ketones and an aldehyde to alkynes proceeded smoothly to give 4 to 7-membered carbocycles bearing an acyl group. When carboxylic anhydrides were used as electrophiles instead of water, the cyclized products could be functionalized with an additional acyl group.

ChemInform Abstract: Catalyst‐Free Formation of 1,4‐Diketones by Addition of Silyl Enolates to Oxyallyl Zwitterions in situ Generated from α‐Haloketones.

Reported here is the exclusive formation of 1,4-diketones by the uncatalyzed reaction of silyl enolates and α-haloketones. Enolates I are inherently more likely to react with α-haloketones II at the carbonyl carbon to produce halohydrin derivatives III or 2-(2-oxoethyl)-oxiranes IV. Thus, a variety of metal-catalyzed coupling reactions have been developed to avoid the undesired reaction when attempting the preparation of 1,4-diketones. We found that the oxyallyl zwitterions in situ generated from α-haloketones enabled the addition of silyl enolates to the α-carbonyl position to exclusively form 1,4-diketones in weakly basic conditions. Various types of silyl enolates and α-haloketones were applied to the catalyst-free coupling.

Catalyst-free formation of 1,4-diketones by addition of silyl enolates to oxyallyl zwitterions in situ generated from α-haloketones

Here we report an efficient and practical method for the preparation of 1,4-diketones by direct coupling of α-haloketones with silyl enolates at room temperature. No catalysts were required in our protocol.

Copper-Catalyzed Enantioselective 1,4-Conjugate Silyl Additions

Correction to: Copper-Catalyzed Enantioselective 1,4-Conjugate Silyl AdditionsSynfacts 2014; 10(04): 0400-0400DOI: 10.1055/s-0033-1341007

Copper-Catalyzed Enantioselective 1,4-Conjugate Silyl Additions

Corrected by: Copper-Catalyzed Enantioselective 1,4-Conjugate Silyl AdditionsSynfacts 2014; 10(05): 0552-0552DOI: 10.1055/s-0033-1341255

ChemInform Abstract: Lewis Acid‐Catalyzed Regioselective Synthesis of Chiral α‐Fluoroalkyl Amines via Asymmetric Addition of Silyl Dienolates to Fluorinated Sulfinylimines.

AbstractThe asymmetric addition of silyl dienolates (II) to sulfinylimines (I) in the presence of catalytic amounts of AgBF4 leads to the α‐adducts (III) as major products, whilst the use of Tms‐O‐Tf as catalyst affords predominantly the γ‐adducts (IV).

Lewis acid-catalyzed regioselective synthesis of chiral α-fluoroalkyl amines via asymmetric addition of silyl dienolates to fluorinated sulfinylimines

A tunable and highly regio- and diastereoselective addition of acyclic silyl dienolates 2 to several α-fluoroalkyl sulfinylimines 1 was developed. By appropriate choice of the Lewis acid catalyst, two new chiral α-fluoroalkyl amines 3 and 4 were obtained in good yields and excellent diastereoselectivities (up to >99 : 1 dr), respectively.

ChemInform Abstract: Enantioselective Conjugate Silyl Additions to α,β‐Unsaturated Aldehydes Catalyzed by Combination of Transition Metal and Chiral Amine Catalysts.

AbstractA combined CuCl—nitrobenzoic acid—prolinol‐derived chiral Tms ether catalyst is successfully applied in the asymmetric hydrosilylation of α,β‐unsaturated aldehydes.

Enantioselective Conjugate Silyl Additions to α,β‐Unsaturated Aldehydes Catalyzed by Combination of Transition Metal and Chiral Amine Catalysts

AbstractWe report that transition metal‐catalyzed nucleophilic activation can be combined with chiral amine‐catalyzed iminium activation as exemplified by the unprecedented enantioselective conjugate addition of a dimethylsilanyl group to α,β‐unsaturated aldehydes. These reactions proceed with excellent 1,4‐selectivity to afford the corresponding β‐silyl aldehyde products 3 in high yields and up to 97:3 er using inexpensive bench stable copper salts and simple chiral amine catalysts. The reaction can also generate a quaternary stereocenter with good enantioselectivity. Density functional calculations are performed to elucidate the reaction mechanism and the origin of enantioselectivity.

ChemInform Abstract: Enantioselective Conjugate Silyl Additions to Cyclic and Acyclic Unsaturated Carbonyls Catalyzed by Cu Complexes of Chiral N‐Heterocyclic Carbenes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Enantioselective Conjugate Silyl Additions to Cyclic and Acyclic Unsaturated Carbonyls Catalyzed by Cu Complexes of Chiral N-Heterocyclic Carbenes

An efficient Cu-catalyzed protocol for enantioselective addition of a dimethylphenylsilanyl group to a wide range of cyclic and acyclic unsaturated ketones, esters, acrylonitriles, and alpha,beta,gamma,delta-dienones is disclosed. Reactions are performed in the presence of 1-2 mol % of commercially available and inexpensive CuCl, a readily accessible monodentate imidazolinium salt, and commercially available (dimethylphenylsilyl)pinacolatoboron. Cu-catalyzed enantioselective conjugate additions proceed to completion within only 2 h to afford the desired silanes in 87-97% yield and 90:10-99:1 enantiomeric ratio (er). Use of a proton source (e.g., MeOH) is not required; accordingly, synthetically versatile alpha-silyl boron enolates can be obtained. The special utility of the present protocol, in comparison with the related catalytic enantioselective aldol and boronate conjugate additions, is discussed and illustrated through various functionalizations of the enantiomerically enriched beta-silylcarbonyls.

Syntheses and crystal structures of azafulleroid and aziridinofullerene bearing silyl or germyl benzene

Abstract Addition of silyl and germylmethyl azides ( 1 ) to fullerene C 60 at 50 °C through [2+3] cycloaddition led to the formation of the triazoline adducts ( 2 ). Subsequently, heating 2 at 100 °C in the solid state, caused N 2 extrusion producing two different isomers, [5,6]-azafulleroid ( 3 ) and [6,6]-aziridinofullerene ( 4 ). The 13 C NMR spectrum of 3 had an absence of resonances in the aliphatic region for the fullerene C 60 cage, showing a fulleroid with C S symmetry. In contrast, 4 exhibited one sp 3 resonance in the aliphatic region for the fullerene C 60 cage, indicative of an aziridinofullerene with C 2V symmetry. However, MALDI-TOF mass characterization was hampered because ion peaks corresponding to the bis-adduct are detected in positive ion mode measurements, whereas the ion peaks [M−N 2 ] − for 2a as well as [M] − for 3a and 4a are observed in negative ion measurements. In an effort to obtain X-ray data, silyl and germylphenyl groups were introduced to form intermolecular complexes with fullerene C 60 . The X-ray structures of 3c and 3d revealed a strong enhancement of homoconjugation in the bridged annulene moiety based on POAV analysis. The X-ray structures of 3c , d and 4c were confirmed with the detection of silyl and germylphenyl-C 60 interactions, similar to dimethoxyphenyl-C 60 interactions.

Reactivity of the silyl, germanyl, and stannyl radicals in addition reactions: The effect of the atomic radius on the activation energy

Experimental data on the addition of silyl, germanyl, and stannyl radicals to olefins are analyzed in the framework of a three intersecting parabolas model. The parameters characterizing these reactions are calculated. The activation energy of the thermally neutral reaction for this class of reactions depends on both the strength of the formed bond and the radius of the atom bearing the free valence. The dependence is the following: E e, 0 1/2 ∼ αD e + bD e 3/2 r C-X 1/2 , where D e is the strength of the formed bond and r C-X is its length. Steric repulsion is observed in the reactions of the silyl radicals with symmetrically substituted ethylene derivatives. The presence of a π-bond or aromatic ring near the attacked double bond increases E e, 0. The increments are calculated that characterize the contribution to the activation energy from the following factors: the enthalpy of the reaction, triplet repulsion, steric hindrance, and effect of adjacent π electrons.

Asymmetric Michael addition of silyl nitronates to cyclic α,β-unsaturated ketones catalyzed by chiral quaternary ammonium bifluorides: isolation and selective functionalization of enol silyl ethers of optically active γ-nitro ketones

Highly enantioselective Michael addition of silyl nitronates to cyclic α,β-unsaturated ketones has been accomplished by the utilization of N-spiro C 2-symmetric chiral quaternary ammonium bifluoride 1 as an efficient catalyst, offering a new route to the enol silyl ethers of optically active γ-nitro ketones. The synthetic utility of this transformation has been demonstrated by the diastereoselective derivatizations of the optically active enol silyl ethers to the corresponding α-substituted cyclic ketones having three consecutive stereochemically defined stereocenters.

Diastereoselective addition of silyl- and stannyl metals to γ-alkoxy-alkylidene malonates

Stereochemical control of the addition of silyl- and stannyl metals to chiral γ-alkoxy-alkylidene malonates proved to be dependant on the nature of the counter ion and of the solvent but in an unpredictable way.

Evaluation of the Relationship Between the Catalyst Structure and Regio‐ as well as Stereoselectivity in the Chiral Ammonium Bifluoride‐Catalyzed Asymmetric Addition of Silyl Nitronates to α,β‐Unsaturated Aldehydes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly diastereoselective mannich-type reactions of chiral N-acylhydrazones.

The Lewis acid-mediated addition of silyl enolates to easily accessible homochiral N-acylhydrazones derived from 3-amino-2-oxazolidinones proceeded in yields up to 71% and diastereomeric ratios of 99:1. In most cases, optimal reaction conditions entailed the simple use of ZnCl(2) in acetonitrile at room temperature. Hydrazones derived from phenyl-, isopropyl-, and benzyl-substituted 2-oxazolidinones were examined in the reaction in terms of yield and diastereoselectivity. The facile SmI(2)-mediated N-N bond cleavage of the formed hydrazines was demonstrated yielding a beta-amino acid derivative. Hence, the overall reaction sequence constitutes an efficient asymmetric Mannich-type reaction. The sense of diastereoselectivity was explained by a preferential attack on the less shielded Si face of the chiral hydrazones and confirmed by means of X-ray crystallography.

Evaluation of the Relationship between the Catalyst Structure and Regio- as well as Stereoselectivity in the Chiral Ammonium Bifluoride–Catalyzed Asymmetric Addition of Silyl Nitronates to α,β-Unsaturated Aldehydes

Abstract Unique relationship between the catalyst structure and regio- and stereoselectivity in the chiral quaternary ammonium bifluoride–catalyzed asymmetric addition of silyl nitronates to α,β-unsaturated aldehydes has been reported.

Highly Enantioselective Michael Addition of Silyl Nitronates to α,β‐Unsaturated Aldehydes Catalyzed by Designer Chiral Ammonium Bifluorides: Efficient Access to Optically Active γ‐Nitro Aldehydes and Their Enol Silyl Ethers.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Highly enantioselective michael addition of silyl nitronates to alpha,beta-unsaturated aldehydes catalyzed by designer chiral ammonium bifluorides: efficient access to optically active gamma-nitro aldehydes and their enol silyl ethers.

Highly enantioselective Michael addition of silyl nitronates to alpha,beta-unsaturated aldehydes has been accomplished by the utilization of designer N-spiro C2-symmetric chiral quaternary ammonium bifluoride 1 as an efficient catalyst, providing direct access to both optically active gamma-nitro aldehydes, a very useful precursor to various complex organic molecules including aminocarbonyls, and their enol silyl ethers, a Mukaiyama donor of potential synthetic utility for further selective transformations. For instance, the reaction of trimethylsilyl nitronate 2 (R1 = Me) with trans-cinnamaldehyde (R2 = Ph, R3 = H) in toluene in the presence of (R,R)-1 (2 mol %) proceeded smoothly at -78 degrees C to give the desired enol silyl ether 3 (R1 = Me, R2 = Ph, R3 = H) in 90% isolated yield (anti/syn = 83:17) with 97% ee (anti isomer), and simple treatment of 3 thus obtained with 1 N HCl in THF at 0 degrees C afforded the corresponding gamma-nitro aldehyde 4 quantitatively without loss of diastereo- and enantioselectivity.