Addition Of Allylsilanes Research Articles

Direct Alkylative Amination using 1-Allylsilatrane.

Homoallylic amines prepared via addition of allylsilanes often require preformed imine substrates, metal catalysts, fluoride activators, or use of protected amines. In this metal-free, air- and water-tolerant procedure, aromatic aldehyde and aniline substrates undergo direct alkylative amination using easily accessible 1-allylsilatrane.

Asymmetric Addition of Allylsilanes to Aldehydes: A Cr/Photoredox Dual Catalytic Approach Complementing the Hosomi–Sakurai Reaction

The allylation of aldehydes is a fundamental transformation in synthetic organic chemistry. Among the multitude of available reagents, allylsilanes especially have been established as a preferred allyl source. As initially reported by Hosomi and Sakurai, these non-toxic and highly stable reagents add to carbonyls via an open transition state upon Lewis acid activation. Herein, we report a general strategy to access a variety of valuable homoallylic alcohols in opposite chemo- and diastereoselectivity to the established Hosomi–Sakurai conditions by switching to photocatalytic activation in combination with a closed transition state (chromium catalysis). Moreover, this dual catalytic approach displays a straightforward way to introduce excellent levels of enantioselectivity and its mild conditions allow for a broad substrate scope including chiral boron-substituted products as a highlight. To emphasize the synthetic utility, our method was applied as the key step in the synthesis of a bioactive compound and in the late-stage functionalization of steroid derivatives. Detailed mechanistic studies and DFT calculations hint toward an unprecedented photo-initiated chain being operative.

Visible‐Light Photoredox‐Catalyzed α‐Regioselective Conjugate Addition of Allyl Groups to Activated Alkenes

AbstractThe α‐regioselective conjugate addition of allyl groups to activated alkenes is a poorly explored area of research. Herein, we report an α‐adduct and (E)‐isomer selective conjugate addition of allylsilanes to activated alkenes by visible‐light photoredox catalysis. The reaction involves allylic radicals that can be generated from allylsilanes through a photoinduced single‐electron transfer mechanism.magnified image

Cationic Cobalt Porphyrin-Catalyzed Allylation of Aldehydes with Allyltrimethylsilanes.

Cationic cobalt porphyrin-catalyzed allylation of aldehydes with allyltrimethylsilanes is developed. The formation of the aldehyde-cobalt porphyrin complex, the key intermediate for the addition of allylsilanes, is confirmed by theoretical studies and synchrotron-based X-ray absorption fine-structure measurements. Facile dissociation of the product by allylation from the cobalt complex regenerates the active complex with the aldehyde. The readily obtainable [Co(TPP)]SbF6 complex serves as an efficient catalyst for this allylation.

B(C6F5)3 catalysed 1,6-conjugate allylation of para-quinone methides: expedient access to allyl diarylmethanes

An efficient protocol for the synthesis of unsymmetrical allyl diarylmethanes through a Lewis acid catalysed 1,6-conjugate addition of allylsilanes to para-quinone methides is described.

ChemInform Abstract: Chiral Phosphine Oxide Aziridinyl Phosphonate as a Lewis Base Catalyst for Enantioselective Allylsilane Addition to Aldehydes.

Abstract A series of chiral Lewis bases, phosphine oxide ferrocenyl aziridinyl methanol 1–4, phosphinyl aziridinyl phosphonates 5 and 6, and phosphine oxide aziridinyl phosphonates 7 and 8 were screened for allylsilane additions to aldehydes. Among the Lewis bases, 8 was found to catalyze the reaction by forming the product in up to 94% yield and with 77% ee.

Chiral phosphine oxide aziridinyl phosphonate as a Lewis base catalyst for enantioselective allylsilane addition to aldehydes

A series of chiral Lewis bases, phosphine oxide ferrocenyl aziridinyl methanol 1–4, phosphinyl aziridinyl phosphonates 5 and 6, and phosphine oxide aziridinyl phosphonates 7 and 8 were screened for allylsilane additions to aldehydes. Among the Lewis bases, 8 was found to catalyze the reaction by forming the product in up to 94% yield and with 77% ee.

ChemInform Abstract: Addition of Allylsilanes and Silyl Enol Ethers to Small Oxygenated Rings: New Tools for Organic Synthesis

AbstractReview: 103 refs.

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.

Addition of Allylsilanes and Silyl Enol Ethers to Small Oxygenated Rings: New Tools for Organic Synthesis

Stereoselective synthesis of new C-C bonds is one of the main objectives of organic chemistry. In this field, silyl activation of alkenes is a useful organic tool in a huge number of Lewis acid promoted reactions due to the ability of the silicon to stabilize neighboring cations. This review summarizes the Lewis acid promoted addition of silyl enol ethers and allylsilanes to epoxides and other small oxygenated rings, which has proved to be an efficient method of synthesis of asymmetric alcohols and other target compounds.

ChemInform Abstract: Synthesis of Spirocarbamate Oxindoles via Intramolecular Trapping of a β‐Silyl Carbocation by an N‐Boc Group.

We report the Lewis acid catalyzed additions of allylsilanes to N-Boc-iminooxindoles and the formation of novel silicon-containing spirocarbamates via intramolecular trapping of a β-silyl carbocation by an N-Boc group. Several transformations display the synthetic utility of these spirocarbamate oxindoles, including a reductive cyclization to access new silylated furoindoline derivatives.

Synthesis of Spirocarbamate Oxindoles via Intramolecular Trapping of a β-Silyl Carbocation by an N-Boc Group

We report the Lewis acid catalyzed additions of allylsilanes to N-Boc-iminooxindoles and the formation of novel silicon-containing spirocarbamates via intramolecular trapping of a β-silyl carbocation by an N-Boc group. Several transformations display the synthetic utility of these spirocarbamate oxindoles, including a reductive cyclization to access new silylated furoindoline derivatives.

On the stereochemical course of the addition of allylsilanes to aldehydes

Model compounds 3 and 5 have been studied to determine the orientation of the reacting double bonds in the transition state of the allylmetal–aldehyde addition. These models were designed to remove any intrinsic steric bias for the formation of the bicyclic products that would obfuscate a stereoelectronic contribution to the transition states. Model system 3 revealed a modest preference for the synclinal transition state, albeit in very low yields. Model system 5 underwent selective and largely Lewis acid independent cyclization primarily via a synclinal transition state. The high proximal selectivity observed in these cyclizations likely reflects the selectivity of an unhindered allylmetal–aldehyde addition for the synclinal transition state and results from a stereoelectronic preference, not an intrinsic steric bias, for the synclinal arrangement of double bonds.

ChemInform Abstract: Intramolecular Additions of Allylsilanes to Conjugated Dienones. Direct Stereoselective Syntheses of (.+-.)-Neolemnanyl Acetate and (.+- .)-Neolemnane.

The total synthesis of the marine sesquiterpenes neolemnanyl acetate (1) and neolemnane (2) is reported. An intramolecular allylsilane addition to a conjugated dienone is used to assemble the basic 6,8-fused skeleton. Functionalization of the cyclooctane ring was achieved by means of a regiospecific photooxygenation

ChemInform Abstract: Stereoselective Conjugate Additions of Allyl Silanes and Enol Silyl Ethers to a Chiral 2-Substituted 2-Cyclohexen-1-one.

Conjugate additions of allyl silanes (the Sakurai reaction) and enol silyl ethers (the Mukaiyama-Michael addition) to chiral 2-amidocyclohexenone1 occur in excellent yields with high diastereoselectivities.

ChemInform Abstract: Super-Acid Catalysed Addition of Allylsilanes to Carbonyl Compounds; Synthetic and Mechanistic Aspects.

The addition of allyltrimethylsilane 8 to a variety of aldehydes and one ketone (cyclohexanone) was found to be induced by the super-acid TfOH2+B(OTf)4–(Tf CF3SO2). In contrast to the analogous Lewis acid catalysed reaction, only catalytic amounts (0.5–3 mol%) of the super-acid were required. Modest stereoselectivities were observed with the ‘α-chiral’ aldehydes 15, 21 and 24; in the last two cases, the sense of the selectivity was the opposite of that predicted by ‘chelation control’. Application of the method to the addition of but-2-enyltrimethylsilane 29 to benzaldehyde demonstrated that, unlike the fluoride-catalysed analogue, it is regioselective with respect to allylic inversion. Control experiments employing Me3SiOTf, B(OTf)3 or TfOH as catalysts established that none is sufficiently active to account for the results. Two possible mechanisms are postulated, one in which the activating species is a superacidic proton and one in which it is an ‘Me3Si+’ unit. On the basis of the stereochemical results, it is argued that the latter is marginally more likely.

Titanium-Induced Ring Opening of a Strained Bicyclic Acetal

Substituted tetrahydrofurans are a common structural motif found in numerous natural and medicinal compounds. The diastereoselective synthesis of trans-2,5-disubstituted tetra­hydrofurans has been studied by the groups of Reißig (Eur. J. Org. Chem. 2000, 3893) and Woerpel (J. Am. Chem. Soc. 2005, 127, 10879). In both cases, the addition of allyl silanes to five-membered cyclic oxacarbenium ions gave poor diastereoselectivities. In the present paper, the use of bicyclic 1 and TiCl4 promotes the ring opening by various C-nucleophiles to provide functionalized trans-substituted products in high selectivities.

Allyl Silane Additions to Highly Electrophilic 5,6-Dihydro-2H-1,4- oxazinones

Allyl Silane Additions to Highly Electrophilic 5,6-Dihydro-2H-1,4- oxazinones

Enantioselective Conjugate Allylation of Activated a,b-Enones

Even though there are several highly effective protocols for the addition of allylsilanes to carbonyl compounds, the methods for asymmetric 1,4-addition are still rare. In this report by Snapper’s group a highly efficient method for the introduction of an allyl group in an asymmetric 1,4-addition manner is described. The reaction proceeds under mild conditions to provide products in high yield and moderate to high enantioselectivities.

Indium(III) Salt Promoted Intramolecular Addition of Allylsilanes to Unactivated Alkynes.

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