Vinyl Boronates Research Articles

A lactam-derived vinyl boronate as a stable and crystalline reagent for the synthesis of 2-substituted piperidines by Pd-catalyzed coupling reactions

A δ-valerolactam-derived vinyl triflate has been converted into the corresponding vinyl boronate by Pd-catalyzed coupling with bis(pinacolato)diboron, which results in an umpolung. This boronate efficiently couples under Pd catalysis with aryl and heteroaryl bromides to give the corresponding 2-substituted piperidines in excellent yields.

Synthesis of Functionalized Vinyl Boronates via Ruthenium‐Catalyzed Olefin Cross‐Metathesis and Subsequent Conversion to Vinyl Halides.

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Synthesis of functionalized vinyl boronates via ruthenium-catalyzed olefin cross-metathesis and subsequent conversion to vinyl halides.

Functionalized vinyl pinacol boronates suitable for Suzuki cross-coupling reactions are synthesized using ruthenium-catalyzed olefin cross-metathesis of 1-propenyl pinacol boronate and various alkenes, including functionalized and 1,1-disubstituted alkenes. The resultant boronate cross products are stereoselectively transformed into predominantly Z-vinyl bromides and E-vinyl iodides. The vinyl bromides may be synthesized in a two-step, one-pot synthesis from a variety of olefins, resulting in a Z-selective formal vinyl bromide cross-metathesis reaction.

Palladium-imidazolium carbene catalyzed aryl, vinyl, and alkyl Suzuki-Miyaura cross coupling.

[reaction--see text] N,N-Bis-(2,6-diisopropylphenyl)dihydroimidazolium chloride with palladium(II) acetate (2 mol %) was used as catalyst, without added base, to efficiently cross couple aryl, vinyl, and alkyl boronates and boronic acids with aryldiazonium tetrafluoroborate substrates. The reactions were performed at 0 degrees C or rt, giving product in 2 to 4 h with 80 to 90% yields for isolated materials. Diazonium ions, formed in situ, also cross couple under these conditions.

Highly Stereoselective Palladium Catalysed Cross-Coupling Approaches to the Total Synthesis of Phthoxazolin A

The first total synthesis of racemic Phthoxazolin A 4 is described, involving a convergent series of palladium cross-coupling reactions to stereoselectively construct the Z, Z, E-trienyl unit. The most important steps involve using vinylboronate pinacol ester 1 as a vinyl dianion equivalent, by employing a Heck coupling of a vinyl iodide 9 with the vinyl boronate 1, followed by a deboronation–iodination sequence with inversion of alkene stereochemistry to provide a new alkenyl iodide 6. Final Stille coupling of the vinyl iodide 6 with an oxazolyl alkenyl stannane 40 provided Phthoxazolin A 4.

The Influence of Boryl Substituents on the Formation and Reactivity of Adjacent and Vicinal Free Radical Centers

Radicals containing α-boronate substituents were generated by bromine abstraction from 1-bromoalkyldioxaborolanes (boronic esters), by addition to vinyl boronate, and by hydrogen abstraction from alkyldioxaborolanes and observed by EPR spectroscopy. Unsymmetrically substituted α-boronate radicals displayed selective line broadening in their low-temperature spectra from which barriers to internal rotation about •CH2−B(OR‘)OR bonds were found to be 3 ± 1 kcal mol-1. Use of an empirical relationship between barrier height and bond dissociation energy led to BDE[(RO)2BCH2−H] = 98.6 kcal mol-1. Rate constants for hydrogen abstraction from 2,4,4,5,5-pentamethyl-1,3,2-dioxaborolane by tert-butoxyl radicals were determined from competitive EPR and product studies and found to be relatively small, comparable to those of unactivated methyl groups. Hydrogen abstraction from bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)methane was found to be extremely difficult. The structures and energetics of α-boronate radical...

A versatile synthesis of 4-aryl tetrahydropyridines via palladium mediated Suzuki cross-coupling with cyclic vinyl boronates

A simple preparation of cyclic vinyl boronates derived from the vinyl triflates of N-protected tetrahydropyridines is described. Suzuki coupling of the boronates with aryl bromides, iodides and triflates proceeds in good yield to give 4-aryl tetrahydropyridines.

New Approaches to Olefin Cross-Metathesis

New methodology for the selective cross-metathesis (CM) of terminal olefins employing ruthenium benzylidene 1 is described.1 CM with symmetric internal olefins was found to provide a useful means for homologating terminal olefins to protected allylic alcohols, amines, and esters. Due to the limited commercial availability of symmetric internal olefins, a two-step CM procedure was developed in which terminal olefins were first homodimerized prior to the CM reaction. Terminal olefins with allylic methyl substituents were observed to provide CM products in diminished yield albeit with markedly improved trans-selectivity. Reaction rates were measured for CM reactions utilizing butenediol and allyl alcohol derivatives, and the results demonstrated distinct advantages in reaction rate and stereoselectivity for reactions employing the disubstituted olefins. In the course of studies of substrates with allylic oxygen substituents, a new CM application was discovered involving the metathesis of acrolein acetal derivatives with terminal olefins. Acrolein acetals, including asymmetric variants derived from tartaric acid, proved to be exceptionally robust and trans-selective CM substrates. In related work, a pinacol-derived vinyl boronate was also found to be a reactive CM partner, providing a novel means for converting terminal olefins into precursors for the Suzuki coupling reaction.

Titanocene Borane σ-Complexes

The chemistry of titanocene bisborane complexes Cp2Ti(HBcat‘)2 (1a−g) (HBcat‘ = catecholborane or a substitued catecholborane) and monoborane complexes Cp2Ti(HBcat‘)(L) (2−4) (L = PMe3, PhSiH3, or PhCCPh) is reported. These complexes are unusual σ-complexes. The B−H bond in the catecholborane of 1 acts as a two-electron-donor ligand. The 4-tert-butyl version 1a was studied in depth and underwent ligand substitution reactions with PMe3, CO, PhSiH3, and PhCCPh. The products of the reaction of 1a with PMe3 and PhSiH3 are the novel monoborane σ-complexes Cp2Ti(HBcat‘)(PMe3) (2a; HBcat‘ = HBO2C6H3-4-t-Bu) and Cp2Ti(HBcat‘)(PhSiH3) (3; HBcat‘ = HBO2C6H3-4-t-Bu), in which the catecholborane remains a two-electron-donating ligand. Reaction with CO formed Cp2Ti(CO)2. Reaction with PhCCPh formed Cp2Ti(HBcat‘)(PhCCPh) (4; HBcat‘ = HBO2C6H3-4-t-Bu), which was observed in solution and reductively eliminated the vinyl boronate ester (Ph)(Bcat‘)CC(Ph)(H). The rates for the reactions of 1a with these substrates showed a ...

4 S,5 S-[Bis(carbethoxy)]-2-ethenyl-1,3,2-dioxaborolane: a novel enantioselective dienophile

The novel chiral vinyl boronate (+)-1 was utilized as a dienophile in a series of [4+2] cycloadditions. The intermediate cyclized products obtained were oxidized directly (H 2O 2, NaOH). The resulting alcohols displayed enantiomeric excesses of 7–33%. A slight preference for the endo configuration was observed, in agreement with previous results.

Absolute Configuration and Total Synthesis of (+)-Curacin A, an Antiproliferative Agent from the Cyanobacterium Lyngbya majuscula

The absolute configuration of curacin A was determined as (2R,13R,19R,21S)-1 by comparison of degradation products 2 and 3 with the same materials prepared by asymmetric synthesis. The total synthesis of 1 was completed from (1R,2S)-2-methylcyclopropanecarboxylic acid (8) and the amino alcohol derivative 46. The latter was prepared from 4-pentynal (14) and the Garner aldehyde (43). Asymmetric allylation of 14 followed by methylation of the derived alcohol 16 gave 17, which was subjected to zirconation−iodination to yield 18. The latter was coupled to the vinyl boronate 21, prepared from 4-pentynyl acetate (20), in the presence of Pd(0), and the resultant trienol 22 was converted to phosphonium iodide 24. Wittig reaction of the ylide from 24 with 43 afforded tetraene 44 which produced 45 upon methanolysis. The mesylate 46 was advanced to thioester 48 either by direct coupling with potassium thiolate 47 obtained from (−)-8 or indirectly via 49. The amino thioester liberated from 48 underwent thermal cycliza...

A novel and efficient route to (E)-alk-1-enyl boronic acid derivatives from (E)-1-(trimethylsilyl)alk-1-enes and a formal Suzuki–Miyaura cross-coupling reaction starting with vinylsilanes

A novel and highly efficient conversion of vinylsilanes into vinyl boronates is described together with their Suzuki–Miyaura cross-coupling reaction, performed without isolating the intermediate resulting from borodesllyiation.

Regioselective synthesis and cross coupling reactions of 1,2-borostannyl-1-alkenes

The copper (I) catalyzed addition of Bu 3Sn⊝BOCH 3⋑ Li⊕ to 1-alkynes yields lithium[2-tri- n -butylstannyl-(Z)-1-alkenyl]-1-borates which may be selectively coupled via organopalladium or organocuprate chemistry with a variety of electrophiles, exclusively at the vinyl boron bond. Products of opposite regiochemistry are obtained when BF 3·Et 2O is added to the initial reaction and the reaction solution is refluxed.

Une méthode simple et efficace de préparation de composés dicarbonylés-1,5

We describe a convenient preparation method of 1,5-dicarbonyl compounds from enol ethers, methyl vinyl ketone and boron triflouride etherate. In the presence of an alcohol, high or quantitative yields are obtained even with enol ethers of hindered ketones. In contrast without alcohol, yields are considerably lower.

Synthesis of Vinyl Bromides Via Reaction of Vinyl Boronic Acids with Sodium Bromide

Abstract Vinyl halides have proven to be useful synthetic intermediates.1,2 Recently, it was discovered that vinyl iodides are more stable to in-vivo deiodination than the corresponding alkyl iodides.3,4 This fact makes the vinyl halides potentially valuable in the design and syntheses of radiopharmaceuticals. Because of our interest in pharmaceutical design, we recently developed a synthesis of vinyl iodides in which vinyl boronic acids are allowed to react with sodium iodide in the presence of mild oxidizing agents.5 The method has been successfully applied to a variety of functionally substituted, physiologically active molecules including fatty acids and steroids.6 We now wish to report that vinyl bromides are readily synthesized via the reaction of vinyl boronic acids with sodium bromide in the presence of mild oxidizing agents such as N-chlorosuccinimide.

Preparation of vinyl boronate copolymers and reactions

Journal of Polymer Science: Polymer Chemistry EditionVolume 20, Issue 7 p. 1949-1952 Note Preparation of vinyl boronate copolymers and reactions J. E. Mulvaney, J. E. Mulvaney Department of Chemistry, University of Arizona, Tucson, Arizona 85721Search for more papers by this authorR. A. Ottaviani, R. A. Ottaviani Department of Chemistry, University of Arizona, Tucson, Arizona 85721Search for more papers by this authorJ. J. Laverty, J. J. Laverty Department of Chemistry, University of Arizona, Tucson, Arizona 85721Search for more papers by this author J. E. Mulvaney, J. E. Mulvaney Department of Chemistry, University of Arizona, Tucson, Arizona 85721Search for more papers by this authorR. A. Ottaviani, R. A. Ottaviani Department of Chemistry, University of Arizona, Tucson, Arizona 85721Search for more papers by this authorJ. J. Laverty, J. J. Laverty Department of Chemistry, University of Arizona, Tucson, Arizona 85721Search for more papers by this author First published: July 1982 https://doi.org/10.1002/pol.1982.170200728Citations: 8AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume20, Issue7July 1982Pages 1949-1952 RelatedInformation

Calculation of the ?-electronic structures of vinyl boron compounds by the free-electron Method

The free-electron model has been used to investigate the π-electronic structures and spectra of two vinylboranes. It is concluded that none of the simple F. E. methods is satisfactory alone and agreement between calculated and observed spectral quantities is only obtained when electron interaction is explicitly included in the calculations.