Addition Of Silyl Enol Ethers Research Articles

Amidyl Radical Directed γ‐C(sp3)−H Functionalization with Silyl Enol Ethers via Photoredox Catalysis

AbstractHerein we reported an efficient photoredox‐catalyzed reaction for site‐selective C(sp3)−H functionalization of carboxamides with silyl enol ethers as radical acceptors. The reaction proceeded through amidyl radical‐directed 1,5‐hydrogen atom transfer (1,5‐HAT) and C(sp3)−C(sp3) bond formation via radical addition of silyl enol ethers. The process features mild conditions and high functional‐group tolerance, allowing the preparation of a series of carboxamides with pendant carbonyl moieties.

Rhenium-Catalyzed Decarboxylative Coupling of Cyclic Enol Carbonates with Silyl Enol Ethers and Ketene Silyl Acetals

The Lewis acid-catalyzed decarboxylative coupling of cyclic enol carbonates, prepared by the fixation of carbon dioxide onto propargyl alcohols, with silyl enol ethers including ketene silyl acetals, was developed to afford 1,4-dicarbonyl compounds in good-to-high yields. As the plausible reaction mechanism, it was proposed that the decarboxylative formation of an oxyallyl cation intermediate or its equivalent and the sequential nucleophilic addition of silyl enol ethers proceeded to afford 1,4-dicarbonyl products. In addition, the synthetic utility of the obtained-1,4-dicarbonyl compounds was also demonstrated by applying them to the construction of multisubstituted heterocycles.

Iron-Catalyzed Highly Enantioselective Addition of Silyl Enol Ethers to α,β-Unsaturated 2-Acyl Imidazoles.

A chiral FeII(N4) complex (N4 = (R,R)-N,N'-bis(2-isopropylquinolin-8-yl)-1,2-diphenylethane-1,2-diamine) was developed for the asymmetric conjugate addition of silyl enol ethers, including both acyclic ones and cyclohexenone-derived ones, to α,β-unsaturated 2-acyl imidazoles. This FeII complex is an effective chiral Lewis acid and was applied in the synthesis of an array of chiral 1,5-dicarbonyl synthons and cyclohexenone derivatives with high yields and enantioselectivities (up to 99% ee).

Copper‐Catalyzed Enantioselective Mukaiyama Aldol Reaction of Silyl Enol Ethers with Isatin‐Derived Oxindolyl β,γ‐Unsaturated α‐Keto Esters

AbstractEnantioselective Mukaiyama 1,2 addition of silyl enol ethers with oxindolyl β,γ‐unsaturated α‐keto esters was developed under catalysis of a chiral L−Cu complex. The reaction was carried out rapidly under mild conditions, to give rise to a series of chiral β‐hydroxyl carbonyl compounds bearing oxindolyl backbone skeleton with high yields and excellent enantioselectivities, up to 99 %, as well as moderate to great diastereoselectivities, up to >20 : 1. This method provided an elegant synthesis route for the synthesis of such compounds.

Stereoselective Synthesis of β-Amino Ynones by the Addition of Alkynones to Nonracemic Sulfinimines: Formal Total Synthesis of l-Xylo and l-Arabino Phytosphingosines

The addition of silyl enol ethers obtained from ynones to sulfinimines furnished the corresponding β-sulfinamido ynones in a very good yield and diastereoselectivity. The formed ynones serve as precursors amenable for the synthesis of bioactive compounds. This has been illustrated in the synthesis of l-xylo and l-arabino phytosphingosines.

DFT investigation on Lewis base-catalyzed Lewis acid-mediated reactions: hypervalent silicon species as chiral organocatalysts in (direct) aldol reactions

The stereoselective organocatalytic addition of silyl enol ethers to aromatic aldehydes catalyzed by bisphosphoramides and the direct aldol reaction between ketones and aromatic aldehydes promoted by phosphinoxides in the presence of tetrachlorosilane were investigated by the DFT approach.

Chiral Zinc(II)-Catalyzed Enantioselective Tandem α-Alkenyl Addition/Proton Shift Reaction of Silyl Enol Ethers with Ketimines.

A new catalytic asymmetric tandem α-alkenyl addition/proton shift reaction of silyl enol ethers with ketimines was serendipitously discovered in the presence of chiral N,N'-dioxide/ZnII complexes. The proton shift preferentially proceeded instead of a silyl shift after α-alkenyl addition of silyl enol ether to the ketimine. A wide range of β-amino silyl enol ethers were synthesized in high yields with good to excellent ee values. Control experiments suggest that the Mukaiyama-Mannich reaction and tandem α-alkenyl addition/proton shift reaction are competitive reactions in the current catalytic system. The obtained β-amino silyl enol ethers were easily transformed into β-fluoroamines containing two vicinal tetrasubstituted carbon centers.

Chiral Zinc(II)‐Catalyzed Enantioselective Tandem α‐Alkenyl Addition/Proton Shift Reaction of Silyl Enol Ethers with Ketimines

AbstractA new catalytic asymmetric tandem α‐alkenyl addition/proton shift reaction of silyl enol ethers with ketimines was serendipitously discovered in the presence of chiral N,N′‐dioxide/ZnII complexes. The proton shift preferentially proceeded instead of a silyl shift after α‐alkenyl addition of silyl enol ether to the ketimine. A wide range of β‐amino silyl enol ethers were synthesized in high yields with good to excellent ee values. Control experiments suggest that the Mukaiyama–Mannich reaction and tandem α‐alkenyl addition/proton shift reaction are competitive reactions in the current catalytic system. The obtained β‐amino silyl enol ethers were easily transformed into β‐fluoroamines containing two vicinal tetrasubstituted carbon centers.

Synthesis of β-Amino Ketones by Addition of Aryl Methyl Ketones to Sulfinimines: Application to the Total Synthesis of HPA-12, Norsedamine, and Sedamine.

Synthesis of β-sulfinamido ketones was accomplished by the addition of silyl enol ethers derived from arylmethyl ketones to chiral sulfinimines in excellent yield and selectivity. Application of the formed β-amino substituted ketones is exemplified in the total synthesis of sphingolipid HPA-12 and the sedamine alkaloids.

Aminophosphine Oxides: A Platform for Diversified Functions.

This review summarizes significant contributions reported on aminophosphine oxides (AmPOs), specifically those containing at least one amino group present as amino substituents on α- and β-carbons including direct P-N bond containing molecules. AmPOs have additional 'N' site(s), including highly basic 'P=O' groups, and these features make favor smooth and unexpected behavior. The most striking manifestations of flexibility of AmPOs are that they are exciting ligand systems for the coordination chemistry of actinides, and their involvement in catalytic organic reactions including enantioselective opening of meso-epoxides, addition of silyl enol ethers, allylation with allyltributylstannane, etc. The diverse properties of the AmPOs and their metal complexes demonstrate both the scope and complexity of these systems, depending on the basicity of phosphoryl group, and nature of the substituents on the pentavalent tetracoordinate phosphorus atom and metal. Two components key to understanding the challenges of actinide separations are detailed here, namely, previously described separation methods, and recent investigations into the fundamental coordination chemistry of actinides. Both are aimed at probing the critical features necessary for improved selectivity of separations. This review leads to the conclusion that, although many AmPOs have already been discovered and developed over the past century, many opportunities nevertheless exist for further developments towards new extraction processes and new catalytic materials by fine tuning the electronic and steric properties of substituents on the central phosphorus atom.

Synthesis of β-Amino-Substituted Enones by Addition of Substituted Methyl Enones to Sulfinimines: Application to the Total Synthesis of Alkaloids (+)-Lasubine II and (+)-241D and the Formal Total Synthesis of (-)-Lasubine I.

Addition of silyl enol ethers obtained from substituted methyl enones to chiral sulfinimines afforded the β-amino-substituted enones with excellent selectivity. Utility of the obtained N-sulfinyl β-amino ketones possessing α,β-unsaturation is exemplified in the total synthesis of the quinolizidine alkaloid natural products (-)-lasubine I, (+)-lasubine II, and substituted piperidine alkaloid (+)-241-D.

Calcium catalyzed Mukaiyama–Mannich addition of silyl enol ethers to nitrones

A method for synthesizing β-(silyloxy)amino carbonyls through the addition of ketone-derived silyl enol ethers to N-phenyl nitrones has been developed. The transformation is catalyzed by a commercially available calcium(II) complex affording β-(silyloxy)amino carbonyls in good to excellent yield.

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: Access to 2‐Alkyl Chromanones via a Conjugate Addition Approach.

AbstractThe introduction of alkyl substituents is performed via conjugate addition of silyl enol ethers to chromenones in the presence of TmsOTf.

Access to 2-alkyl chromanones via a conjugate addition approach

The introduction of alkyl substituents at C-2 of chromanones via conjugate addition of silyl enol ethers to a variety of chromenones is reported. In most cases racemic 2-alkyl chromanones were obtained in good yield in the presence of TMSOTf. The copper(II)-promoted conjugate addition of silyl enol ethers to chromenones was also carried out, albeit in low yields and no selectivity. Reliable syntheses of the chromenones via acylation of the corresponding β-diketo-compounds are also described.

ChemInform Abstract: Rapid, One‐Pot Synthesis of β‐Siloxy‐α‐haloaldehydes.

AbstractA Mukaiyama cross‐aldol addition of silyl enol ethers derived from α‐halogenated acetaldehydes is reported.

Highly enantioselective catalytic synthesis of functionalized chiral diazoacetoacetates.

The Michael reaction is one of the most general and versatile methods for carbon-carbon bond formation,1 and its Mukaiyama-Michael variant provides an efficient strategy for the addition of silyl enol ethers to α,β-unsaturated carbonyl compounds.2 Catalytic asymmetric reactions with broad variations in α,β-unsaturated carbonyl compounds and chiral catalyst (Lewis acid and Bronsted acid) are well documented,3,4 and the enantioenriched 1,5-dicarbonyl compounds formed from these reactions have proven to be useful building blocks. However, there has been limited variation in the silyl enol ethers used in these reactions, and none of them have incorporated multiple functional groups.

Synthesis of 2-substituted 7-hydroxybenzofuran-4-carboxylates via addition of silyl enol ethers to o-benzoquinone esters.

Mukaiyama Michael addition of silyl enol ethers 13 to the 1,2-quinone-4-carboxylate 6 (formed in situ by oxidation of the catechol ester 8) afforded the 2-subsituted 7-hydroxybenzofuran-4-carboxylates 14 in fair to good yields. Alkyl and aryl systems work well, but highly electron-rich silyl enol ethers could not be used because of competing oxidation.

Palladium‐Catalyzed Enantioselective Cyclization of Silyloxy‐1,6‐enynes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Palladium-Catalyzed Enantioselective Cyclization of Silyloxy-1,6-Enynes

The enantioselective intramolecular addition of silyl enol ethers and silyl ketene aminals onto alkyne is described. The reaction employs DTBMSegphos−Pd(II) or Binaphane−Pd(II) complexes as catalysts for the formation of methylene cyclopentane adducts from 1,6-enyne precursors. The utility of this reaction is illustrated by its application to the total synthesis of the cytotoxic cyclolaurane-type sesquiterpene, (−)-laurebiphenyl.