Ynol Ethers Research Articles

Combined Carbometalation–Zinc Homologation–Allylation Reactions as a New Approach for Alkoxyallylation of Aldehydes

The combined carbometalation reaction of ynol ethers followed by a zinc homologation and further allylation reactions lead to an efficient preparation of allylic vicinal diols. The stereochemical outcome of the reaction shows that the substituent of the aldehyde occupies a pseudoaxial position in a Zimmerman-Traxler transition state.

ChemInform Abstract: Intramolecular Regioselective Addition of Radicals and Carbanions to Ynol Ethers. A Strategy for the Synthesis of Exocyclic Enol Ethers.

AbstractTwo new strategies to synthesize exocyclic enol ethers are presented.

Dichloroenol Ethers X-ray Analysis in the Mechanistic Elucidation of Ynol Ethers Formation

AbstractX-ray crystallographic data are provided for dichloroenol ethers (S,E)-2-(1-(1,2-dichlorovinyloxy)ethyl)-1,3,5-triisopropylbenzene (2) and (S,E)-2-(1-(1,2-dichloroprop-1-enyloxy)ethyl)-1,3,5-triisopropylbenzene (3). The former forms colorless crystals (orthorhombic, P2 1 2 1 2 1 space group) and exhibits the following cell parameters: a = 10.212(5) A; b = 10.359(8) A; c = 18.217(6) A. The latter also affords colorless crystals (monoclinic, P2 1 space group) with a = 13.558(2) A; b = 10.891(1) A; c = 15.260(2) A; β = 115.65(1)°. The data complement those recently reported for two other dichloroenol ethers, ((1R,2S)-2-((E)-1,2-dichlorovinyloxy)cyclohexyl)benzene (5) and ((1R,2S)-2-((E)-1,2-dichloroprop-1-enyloxy)cyclohexyl)benzene (6). The X-ray analyses of these dichloroenol ethers, the only reported to date, establish unambiguously the trans stereochemistry of the chlorides in these and, by extension, similarly prepared enol ethers. This information was required for the complete mechanistic understanding of ynol ethers formation from dichloroenol ethers. Structural comparison of these dichloroenol ethers with some carbon (dichloroalkene) and nitrogen (dichloroenamine) analogues is also presented.Graphical AbstractThis article reports the X-ray structures of four dichloroenol ethers, which establish the trans relationship of the chlorides. This determination of configuration is the starting point for the mechanistic elucidation of ynol ether formation from dichloroenol ethers.[IMAGE]

Site-specific introduction of gold-carbenoids by intermolecular oxidation of ynamides or ynol ethers

Ynamides and ynol ethers undergo intermolecular gold-catalysed reaction with a nucleophilic oxidant to access metal-carbenoid reactivity patterns. A site-specific oxidation/1,2-insertion cascade is used for a general access to functionalised α,β-unsaturated carboxylic acid derivatives and vinylogous carbimates.

Palladium-catalyzed haloallylation of aromatic ynol ethers with allyl chlorides: a highly regio- and stereoselective approach to (1E)-α-chloroenol ethers

Described herein is a Pd-catalyzed haloallylation of aromatic ynol ethers and allyl chlorides, allowing facile access to (1E)-α-chloroenol ethers in a highly regio- and stereoselective manner. The synthetic utility of this method is demonstrated well by the synthesis of the stereodefined multisubstituted enol ethers and α-allylated carbonyl compounds.

Intramolecular regioselective addition of radicals and carbanions to ynol ethers. A strategy for the synthesis of exocyclic enol ethers

The scope and limitations of radical and anionic cyclization reactions involving halo ynol ethers have been investigated. 5- exo and 6- exo radical cyclizations of 6-iodo and 7-iodo ynol ethers proceeded well when the oxygen of the ynol ether was bearing an ethyl group. Exocyclic iodoenol ethers resulting from these cyclizations were highly unstable and decomposed rapidly. Li–I exchange of iodo ynol ethers proceeded smoothly at −78 °C. 6-Alkoxy-5-hexynyllithiums underwent regiospecific 5- exo-dig anionic cyclization to produce five-membered rings bearing an exocyclic enol ether moiety. The cyclized vinyllithium intermediate was successfully trapped with electrophiles to afford functionalized cycloalkoxyalkylidene derivatives in modest to good yields. 7-Alkoxy-6-heptynyllithiums did not cyclize via a 6- exo anionic process.

ChemInform Abstract: Camphor-Derived Alcohols as Chiral Auxiliaries for Asymmetric Pauson- Khand Bicyclizations. Enantioselective Synthesis of α- Methoxyenones.

Abstract The intramolecular Pauson-Khand reaction of enol and ynol ethers of Oppolzer's camphor-derived neopentyloxy alcohols is described. Bicyclic products are obtained in yields of up to 65% and with diastereoselectivities as high as 94:6 under very mild reaction conditions. The absolute configurations of the major stereoisomers obtained when (1R, 2S, 3R, 4S)-3-neopentyloxy-1,7,7-trimethylbicyclo- [2.2.1]heptan-2-ol is used as a chiral auxiliary are rationalized on the basis of the theoretically predicted preferential conformations of model precursors. A simple procedure for obtaining auxiliary-free, enantiopure bicyclic α-methoxyenones is also presented.

Regiodivergent Carbometalation Reactions of Ynol Ether Derivatives

The stereodivergent carbometalation of substituted ynol ethers is reported and both isomers could be obtained at will depending of the nature of the OR group.

Nickel-Catalyzed [3 + 2 + 2] Cycloaddition of Ethyl Cyclopropylideneacetate and Heteroatom-Substituted Alkynes: Application to Selective Three-Component Reaction with 1,3-Diynes

Heteroatom-substituted alkynes such as ynol ethers and ynamines turned out to be decent substrates for the Ni-catalyzed [3 + 2 + 2] cocyclization of ethyl cyclopropylideneacetate (1). The three-component cocyclization of 1, 1,3-diynes, and heteroatom-substituted alkynes also proceeded selectively. The study provided an efficient method for the synthesis of heteroatom-substituted cycloheptadiene and related compounds.

ChemInform Abstract: Radical Addition to Ynol Ethers — A Convenient Procedure for the Stereoselective Preparation of α‐Iodo Enol Ethers in Neutral Conditions.

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 of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Radical addition to ynol ethers — A convenient procedure for the stereoselective preparation of α-iodo enol ethers in neutral conditions

α-Iodo enol ethers, precursors of acyl anion equivalents, are not easily prepared. Herein we report that addition of activated iodoalkanes to ynol ethers under mild and neutral radical reaction conditions leads to α-iodo enol ethers in moderate to excellent yields with high stereoselectivity. The reaction can be carried out in various solvents at different temperatures. The methodology allows the preparation of β-alkylated and β,β-dialkylated α-iodo enol ethers. Reduction of the carbon-iodine bond of these species leads to the corresponding enol ethers with good yields.Key words: ynol ethers, enol ethers, radical addition, stereoselective.

Synthesis of cyclopentenones from cyclopropanes and silyl ynol ethers.

Synthesis of cyclopentenones from cyclopropanes and silyl ynol ethers.

Synthesis of Cyclopentenones from Cyclopropanes and Silyl Ynol Ethers

Ringöffnung und Ringschluss: Die Ringöffnung Donor-Akzeptor-substituierter Cyclopropane durch Lewis-Säuren erzeugt 1,3-Zwitterionen, die durch Cycloadditionen mit Silylinolethern Cyclopentenone zugänglich machen (siehe Schema). Am Inol und an allen Positionen des Cyclopropans können Substituenten vorliegen, sodass drei-, vier- und fünffach substituierte Cyclopentenone in hohen Ausbeuten erhalten werden. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2001/2008/z801957_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Water as an efficient medium for the synthesis of functionalized enol ethers

Herein we report an efficient method for synthesis of β-alkylated and β,β-dialkylated α-iodo enol ethers in water. Radical addition in aqueous medium of ethyl iodoacetate, iodoacetonitrile, and iodoacetamide to ynol ethers leads to α-iodo enol ethers with moderate to excellent yields and high stereoselectivities.

2+2+1] Cycloadditions of ynol ethers. The synthesis of iron complexes of 3-alkoxycyclopentadienones

This Letter reports the synthesis of iron complexes of 3-oxocyclopentadienones from ynol ether–alkyne [2+2+1] cycloaddition reactions as well as the use of 3-alkoxycyclopentadienones in subsequent cycloaddition reactions.

ChemInform Abstract: Synthesis of Ynamides and Ynol Ethers via Formamides and Formates.

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.

Silylation and germylation of trialkylsilyl(germyl)ethoxyacetylenes containing bulky substituents at the silicon or germanium atom

Silylation and germylation of trialkylsilyl(germyl)ethoxyacetylenes containing bulky substituents at the silicon or germanium atom were performed. In all cases, the corresponding bis-organoelement-containing ketenes were obtained as the only reaction products. No intermediate isomeric ynol ethers were detected by spectroscopy.

Synthesis of Ynamides and Ynol Ethers via Formamides and Formates

Synthesis of Ynamides and Ynol Ethers via Formamides and Formates

A General, Catalytic, and Enantioselective Synthesis of (S)-γ-[(S)-1-Aminoalkyl]-γ-lactones

A catalytic asymmetric synthesis of N-phthaloyl (S)-γ-[(S)-1-aminoalkyl]-γ-lactones, widely used intermediates in the preparation of hydroxyethylene dipeptide isosteres, is described. The highly enantiopure epoxy alcohols arising from the Sharpless epoxidation of (E)-allyl alcohols are first converted to (S)-N-phthaloyl-[(S)-1-aminoalkyl]oxiranes by means of an efficient four-step sequence involving the regio- and stereoselective ring opening of the starting epoxide by azide, reduction, phthaloylation, and intramolecular Mitsunobu cyclization of the intermediate phthalimido diol. Treatment of the resulting oxirane with lithium (1R)-menthyloxyacetylide in the presence of boron trifluoride etherate, followed by in situ hydrolysis of the ynol ether, leads to a (4R,5S)-5-phthalimido-4-hydroxy ester. A Mitsunobu reaction with p-nitrobenzoic acid (which establishes the correct (S)-configuration at C-4) and subsequent selective saponification of the benzoate and cyclization of the inverted hydroxy ester afford the target N-protected (S)-γ-[(S)-1-aminoalkyl]-γ-lactones. Using this methodology, lactones 19 and 26 were obtained in seven steps from the readily available epoxy alcohols 5 and 20, respectively, in high enantiomeric purity.

Carbene Complex Modified Glycals: Synthesis and Reactivity

New opportunities in the functionalization of carbohydrates arise from carbene complex modified glycals. They undergo a chromium-induced benzannulation to give benzoglycals 1 and allow a C2-homologization to 2 with retention of the metal–carbene bond by a diastereoselective insertion of ynol ethers.