Propargyl Silyl Ethers Research Articles

One-Pot, Three-Step Synthesis of Cyclopropylboronic Acid Pinacol Esters from Synthetically Tractable Propargylic Silyl Ethers.

Simple propargylic silyl ethers can be converted to complex cyclopropylboronic acid pinacol esters in an efficient one-pot procedure. Terminal acetylenes undergo a Schwartz's reagent catalyzed hydroboration; subsequent addition of further Schwartz's reagent and Lewis acid-mediated activation of neighboring silyl ether allows cyclization to access a range of cyclopropylboronic acid pinacol esters. The scope includes aromatic, aliphatic, quaternary, and spiro substituted cyclopropyl rings, which can be transformed via Suzuki coupling into a range of lead-like substituted cyclopropyl aryl products.

ChemInform Abstract: An Efficient Approach Toward Formation of Polycyclic Coumarin Derivatives via Carbocation‐Initiated [4 + 2] Cycloaddition and Atom‐Economical Photo‐Irradiated Cyclization.

Facile carbocation-initiated [4+2] cycloaddition of o-anisole-substituted propargyl silyl ethers and ynamides led to the formation of 4-vinylcoumarins. Subsequent intramolecular cyclization of 3-aryl-4-vinylcoumarins afforded polycyclic coumarin derivatives 11,12-dihydronaphtho[1,2-c]chromen-5-ones in excellent yields under mild photo-irradiated conditions established by fluorescence analysis-oriented screening.

Synthesis of Thioethers by InI₃-Catalyzed Substitution of Siloxy Group Using Thiosilanes.

The substitution of a siloxy group using thiosilanes smoothly occurred in the presence of InI3 catalyst to yield the corresponding thioethers. InI3 was a specifically effective catalyst in this reaction system, while other typical Lewis acids such as BF3·OEt2, AlCl3, and TiCl4 were ineffective. Various silyl ethers such as primary alkyl, secondary alkyl, tertiary alkyl, allylic, benzylic, and propargylic types were applicable. In addition, bulky OSitBuMe2 and OSiiPr3 groups, other than the OSiMe3 group, were successfully substituted. The substitution reaction of enantiopure secondary benzylic silyl ether yielded the corresponding racemic thioether product, which suggested that the reaction of tertiary alkyl, secondary alkyl, benzylic, and propargylic silyl ethers would proceed via a SN1 mechanism.

Gold-Catalyzed Synthesis of Quinolines from Propargyl Silyl Ethers and Anthranils through the Umpolung of a Gold Carbene Carbon.

A gold-catalyzed cascade annulation of propargylic silyl ethers with anthranils proceeds through a sequential ring opening/1,2-H-shift/protodeauration/Mukaiyama aldol cyclization. This method offers a regiospecific and modular access to 2-aminoquinolines and other quinoline derivatives under mild conditions and with a broad functional-group tolerance. The conversion is possible on a gram scale, which underlines the synthetic practicability of this methodology. The versatility of the obtained scaffold has been demonstrated by useful postfunctionalization.

Understanding Initiation with Triethylboron and Oxygen: The Differences between Low-Oxygen and High-Oxygen Regimes.

A unified kinetic theory for both initiation and autoxidation reactions of Et3B and O2 is put forth, and then divided into low-oxygen and high-oxygen experimental regimes for application of Et3B/O2 as an initiating system. In the low-oxygen regime, only long, efficient chains can be initiated. In the high-oxygen regime, less efficient chains can be initiated but they must compete with autoxidation. We apply the analysis along with new experimental results to show why AIBN and Et3B/O2 give different stereochemical results in hydrostannation reactions of propargyl silyl ethers. Counterintuitively, AIBN is the better initiator, initiating both the rapid chain hydrostannation and the subsequent slow E/Z isomerization. AIBN gives the thermodynamic results. Et3B/O2 is the poorer initiator, initiating only the hydrostannation and not the isomerization. Et3B gives the kinetic result. We further apply the analysis to understand recent results in Et3B/water reductions.

Lewis acid catalyzed [2+2] cycloaddition of ynamides and propargyl silyl ethers: synthesis of alkylidenecyclobutenones and their reactivity in ring-opening and ring expansion.

A family of four-membered enones, polysubstituted alkylidenecyclobutenones, were easily prepared by a Lewis acid catalyzed [2+2] cycloaddition of ynamides and propargyl silyl ethers. This challenging regioselective [2+2] cycloaddition enables the efficient construction and conversion of four-membered enones, which provides high-value and structurally diverse products through the unexpected ring-opening and ring expansion of alkylidenecyclobutenone with Grignard reagents, organolithium, primary amines, and water.

An efficient approach toward formation of polycyclic coumarin derivatives via carbocation-initiated [4+2] cycloaddition and atom-economical photo-irradiated cyclization.

Facile carbocation-initiated [4+2] cycloaddition of o-anisole-substituted propargyl silyl ethers and ynamides led to the formation of 4-vinylcoumarins. Subsequent intramolecular cyclization of 3-aryl-4-vinylcoumarins afforded polycyclic coumarin derivatives 11,12-dihydronaphtho[1,2-c]chromen-5-ones in excellent yields under mild photo-irradiated conditions established by fluorescence analysis-oriented screening.

Catalytic Deprotonative Functionalization of Propargyl Silyl Ethers with Imines

AbstractA metal‐free, catalytic CH functionalization of propargyl silyl ethers with imines using the phosphazene base (t‐Bu‐P4 base) provides structurally defined multisubstituted pyrroles in modest to excellent yields under mild conditions. A one‐pot, three‐component reaction using silylated acetylenes, aldehydes, and imines is also presented.

Lewis Acid Catalyzed Nucleophilic Substitutions of Propargylic and Allylic Silyl Ethers with Enol Silyl Ethers.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Lewis acid-catalyzed nucleophilic substitutions of propargylic and allylic silyl ethers with enol silyl ethers.

Nucleophilic reactions of various enol silyl ethers with carbocation species generated from propargyl silyl ethers by the action of a Lewis acid have been developed. The present method is highly useful for the introduction of allenic or enyne functionalities into the alpha-position of substituted ketones. [reaction--see text]

ChemInform Abstract: Novel Carbon—Carbon Bond‐Forming Reactions Using Carbocations Produced from Substituted Propargyl Silyl Ethers by the Action of TMSOTf.

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.

Novel carbon-carbon bond-forming reactions using carbocations produced from substituted propargyl silyl ethers by the action of TMSOTf.

Highly useful carbon-carbon bond forming reactions using stable allenyl, propargyl, or allyl-propargyl hybrid cations have been developed. These carbocations could be generated from silyl 1-(pi-donor)-substituted propargyl ethers by the action of trimethylsilyl trifluoromethanesulfonate in dichloromethane at -78 degrees C to room temperature and could be attacked nucleophilically by electron rich arenes, allylsilanes, or enol silyl ethers, giving rise to allenes, alkynes, and their derivatives. A novel method for regio- and stereoselective synthesis of conjugated enynes utilizing allyl-propargyl hybrid cations has also been established.

Oligonucleosides with a Nucleobase-Including Backbone, Part 2, Synthesis and Structure Determination of Adenosine-Derived Monomers

The synthesis and structure determination of adenosine-derived monomeric building blocks for new oligonucleosides are described. Addition of Me3Si-acetylide to the aldehyde derived from the known partially protected adenosine 1 led to the epimeric propargylic alcohols 2 and 3, which were oxidised to the same ketone 4, while silylation and deprotection led to 7 and 9 (Scheme 1). Introduction of an I substituent at C(8) of the propargylic silyl ethers 10 and 11 was not satisfactory. The protected adenosine 12 was, therefore, transformed in high yield into the 8-chloro derivative 13 by deprotonation and treatment with PhSO2Cl; the iodide 15 was obtained in a similar way (Scheme 2). The 8-Cl and the 8-I derivatives 13 and 15 were transformed into the propargylic alcohols 17, 18, 25, and 26, respectively (Scheme 3). The propargylic derivatives 2, 10, 17, 19, 23, 25, and 27 were correlated, and their (5′R) configuration was determined on the basis of NOEs of the anhydro nucleoside 19; similarly, correlation of 3, 11, 18, 20, 24, 26, and 28, and NOE's of 20 evidenced their (5′S)-configuration.

ChemInform Abstract: Allene Formation by the Reaction of Olefins with Propargyl Silyl Ethers Mediated by a Zirconocene Complex.

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.

Allene formation by the reaction of olefins with propargyl silyl ethers mediated by a zirconocene complex

Ethylene and styrene derivatives reacted with various propargylic ethers in the presence of zirconocene(II) to afford allenic products in high yields. The reaction proceeded via formation of zirconacyclopentenes by selective coupling of an olefin and a propargylic ether, which was followed by β-elimination of the siloxy group. Deuterolysis confirmed that the final product had a zirconium-carbon bond.