Allylic Silanes Research Articles

ChemInform Abstract: Asymmetric Conjugate Addition of Grignard Reagents to 3‐Silyl Unsaturated Esters for the Facile Preparation of Enantioenriched β‐Silylcarbonyl Compounds and Allylic Silanes.

AbstractA highly enantioselective conjugate addition of Grignard reagents to 3‐silyl unsaturated esters to deliver synthetically useful chiral β‐silylcarbonyl compounds is developed.

Temperature-Dependent Direct Enantioconvergent Silylation of a Racemic Cyclic Allylic Phosphate by Copper(I)-Catalyzed Allylic Substitution

The near-quantitative transformation of a racemic cyclic allylic phosphate to a highly enantiomerically enriched allylic silane by allylic substitution with a silicon nucleophile is reported. The reaction is catalyzed by a chiral NHC–copper(I) complex. Experimental analysis revealed a rare case of a direct enantioconvergent transformation where the enantiomeric allylic phosphates converge to the same allylic silane by two distinctive S_N2′ pathways with opposite diastereofacial selectivity.

Regioselective aerobic oxidative Heck reactions with electronically unbiased alkenes: efficient access to α-alkyl vinylarenes.

Branched-selective oxidative Heck coupling reactions have been developed between arylboronic acids and electronically unbiased terminal alkenes. The reactions exhibit high catalyst-controlled regioselectivity favoring the less common branched isomer. The reactions employ a catalyst composed of Pd(TFA)2/dmphen (TFA = trifluoroacetate, dmphen = 2,9-dimethyl-1,10-phenanthroline) and proceed efficiently at 45-60 °C under 1 atm of O2 without requiring other additives. A broad array of functional groups, including aryl halide, allyl silane and carboxylic acids are tolerated.

Intramolecular anion effect in polyoxometalate-based organocatalysts: reactivity enhancement and chirality transfer by a metal oxide-organic cation interaction.

An α1 -Dawson polyanion bearing a lateral side chain with a 4-aminopyridine end group was synthesized. This organopolyoxometalate catalyzes the addition of indenyl allyl silanes to cinnamoyl fluorides. The polyanionic framework influences the organocatalyst activity and selectivity. A moderate but nonzero chirality transfer from the chiral inorganic framework to the organic substrate was observed.

Redox and Lewis acid relay catalysis: a titanocene/zinc catalytic platform in the development of multicomponent coupling reactions.

A titanocene-catalyzed multicomponent coupling is described herein. Using catalytic titanocene, phosphine, and zinc dust, zinc acetylides can be generated from the corresponding iodoalkynes to affect sequential nucleophilic additions to aromatic aldehydes. The intermediate propargylic alkoxides are trapped in situ with acetic anhydride, which are susceptible to a second nucleophilic displacement upon treatment with a variety of electron-rich species, including acetylides, allyl silanes, electron-rich aromatics, silyl enol ethers, and silyl ketene acetals. Additionally, employing cyclopropane carboxaldehydes led to ring-opened products resulting from iodine incorporation. Taken together, these results form the basis for a new mode of three-component coupling reactions, which allows for rapid access to value added products in a single synthetic operation.

Asymmetric Conjugate Addition of Grignard Reagents to 3‐Silyl Unsaturated Esters for the Facile Preparation of Enantioenriched β‐Silylcarbonyl Compounds and Allylic Silanes

A highly enantioselective conjugate addition of Grignard reagents to 3-silyl unsaturated esters to deliver synthetically useful chiral β-silylcarbonyl compounds was developed. The synthetic value of this methodology was further illustrated by the synthesis of enantioenriched β-hydroxyl esters and the facile access granted to various α-chiral allylic silanes. A plethora of diastereoselective transformations of β-silylenolates were also investigated and afforded manifold organosilanes that contained contiguous stereogenic centers with excellent enantioselectivity.

Frustrated Lewis pair catalyzed hydrosilylation and hydrosilane mediated hydrogenation of fulvenes.

The frustrated Lewis pair (FLP) mediated hydrosilylation of pentafulvenes is described yielding allyl silanes with high regioselectivity in excellent yields. While phenyl substituted allyl silanes undergo B(C6F5)3-mediated rearrangement to vinyl silanes, dimethyl derivatives experience FLP-catalyzed hydrogenation followed by an unprecedented protodesilylation. This observation allowed the metal-free hydrogenation of 6,6-dimethylfulvene to iso-propyl cyclopentene according to a FLP-catalyzed triple domino reaction consisting of hydrosilylation, hydrogenation and protodesilylation. The mechanisms were investigated by deuteration experiments.

ChemInform Abstract: Regio‐ and Diastereoselective Copper(I)‐Catalyzed Allylic Substitution of δ‐Hydroxy Allylic Chlorides by a Silicon Nucleophile.

AbstractA new preparation of β‐hydroxy α‐chiral allylic silanes with the anti relative configuration by copper(I)‐catalyzed allylic silyl transfer is accomplished.

ChemInform Abstract: Silyl‐Heck Reactions for the Preparation of Unsaturated Organosilanes

AbstractReview: 36 refs.

Silyl-Heck Reactions for the Preparation of Unsaturated Organosilanes.

Few methods exist to directly install silyl functionality onto olefins. This Synpacts highlights the state of the art of the silyl-Heck reaction and our recently developed conditions for preparing allyl and vinyl silanes from terminal alkenes using this method.

ChemInform Abstract: Asymmetric Synthesis of α‐Chiral Allylic Silanes by Enantioconvergent γ‐Selective Copper(I)‐Catalyzed Allylic Silylation.

Gamma way: Regio- and enantioselective allylic substitution with a silicon nucleophile generated by copper(I)-catalyzed Si-B bond activation provides direct access to α-chiral allylic silanes from linear acceptors. The enantioconvergent catalysis employing McQuade's six-membered N-heterocyclic-carbene-copper(I) catalyst is applicable to aryl- and alkyl-substituted allylic phosphates (see scheme).

Regio‐ and Diastereoselective Copper(I)‐Catalyzed Allylic Substitution of δ‐Hydroxy Allylic Chlorides by a Silicon Nucleophile

AbstractA perfectly γ‐selective copper(I)‐catalyzed allylic substitution of protected δ‐hydroxy allylic chlorides with a silicon nucleophile generated by Si–B bond activation provides diastereoselective access to β‐hydroxy α‐chiral allylic silanes with anantirelative configuration. The high levels of diastereocontrol of this rare allylic displacement are interpreted according to a model suggested by Nakamura where diastereofacial selectivity originates from steric control rather than an oxygen‐directing effect in the Felkin–Anh transition state.

Asymmetric Synthesis of α‐Chiral Allylic Silanes by Enantioconvergent γ‐Selective Copper(I)‐Catalyzed Allylic Silylation

Gamma way: Regio- and enantioselective allylic substitution with a silicon nucleophile generated by copper(I)-catalyzed Si-B bond activation provides direct access to α-chiral allylic silanes from linear acceptors. The enantioconvergent catalysis employing McQuade's six-membered N-heterocyclic-carbene-copper(I) catalyst is applicable to aryl- and alkyl-substituted allylic phosphates (see scheme).

Total synthesis of (±)-leuconolam: intramolecular allylic silane addition to a maleimide carbonyl group.

A concise total synthesis of the plant alkaloid (±)-leuconolam (1) has been achieved. A regio- and diastereoselective Lewis-acid mediated allylative cyclization was used to establish, simultaneously, two adjacent tetrasubstituted carbon centers. Furthermore, an essential arene cross-coupling to a hindered haloalkene was enabled by the use of a novel 2-anilinostannane.

Mechanistic Investigation of the Palladium-Catalyzed Synthesis of Allylic Silanes and Boronates from Allylic Alcohols

The mechanism of the palladium-catalyzed synthesis of allylic silanes and boronates from allylic alcohols was investigated. (1)H, (29)Si, (19)F, and (11)B NMR spectroscopy was used to reveal key intermediates and byproducts of the silylation reaction. The tetrafluoroborate counterion of the palladium catalyst is proposed to play an important role in both catalyst activation as well as the transmetalation step. We propose that BF(3) is generated in both processes and is responsible for the activation of the substrate hydroxyl group. An (η(3)-allyl)palladium complex has been identified as the catalyst resting state, and the formation of (η(3)-allyl)palladium complexes directly from allylic alcohols has been studied. Kinetic analysis provides evidence that the turnover limiting step is the transmetalation, and insights into notable similarities between the borylation and the silylation reaction mechanisms enabled us to considerably improve the stereoselectivity of the borylation.

Efficient Generation of ortho‐Naphthoquinone Methides from 1,4‐Epoxy‐1,4‐dihydronaphthalenes and Their Annulation with Allyl Silanes

Efficient Generation of <i>ortho</i>‐Naphthoquinone Methides from 1,4‐Epoxy‐1,4‐dihydronaphthalenes and Their Annulation with Allyl Silanes

Efficient Generation of ortho‐Naphthoquinone Methides from 1,4‐Epoxy‐1,4‐dihydronaphthalenes and Their Annulation with Allyl Silanes

Efficient Generation of <i>ortho</i>‐Naphthoquinone Methides from 1,4‐Epoxy‐1,4‐dihydronaphthalenes and Their Annulation with Allyl Silanes

Iron‐Catalyzed Diastereoselective Synthesis of α‐(Methoxycarbonyl)allylsilanes

AbstractStereodefined polysubstituted α‐(methoxycarbonyl)allylsilanes were synthesized through iron‐catalyzed conjugate additions between 1‐(trimethylsilyl)allene‐1‐carboxylates and Grignard reagents in good to excellent yields. The use of Et2O as solvent for Grignard reagents was found to be very important for the diastereoselectivity of the reaction. Applications of the prepared allylic silanes for the stereocontrolled synthesis of α,β‐alkenoates, a β,γ‐alkenoate, and an allylic fluoride have been demonstrated.

ChemInform Abstract: Preparation of Allyl and Vinyl Silanes by the Palladium‐Catalyzed Silylation of Terminal Olefins: A Silyl‐Heck Reaction.

AbstractThe use of BPP is the key for the title synthesis.

Diastereoselective Synthesis of Seven-Membered-Ring trans-Alkenes from Dienes and Aldehydes by Silylene Transfer

Silver-catalyzed silylene transfer to alkenes forms vinylsilacyclopropanes regioselectively. These allylic silanes undergo additions to aldehydes to form seven-membered-ring trans-alkenes with high diastereoselectivity. The high reactivity of the trans-alkenes is evidenced by their formal [1,3]-sigmatropic rearrangement reactions and the rapid additions of oxygen-hydrogen bonds across the carbon-carbon double bonds.