Organocatalytic Vinyl and Friedel−Crafts Alkylations with Trifluoroborate Salts (original) (raw)
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Efficient separation of a trifluoromethyl substituted organocatalyst: just add water
Chemical Communications, 2009
General Information. Nuclear Magnetic Resonance spectra (NMR) were acquired on a Varian UNITY INOVA (400 MHz) instrument using CDCl 3 as internal standard and Varian Gemini 2000 (200 MHz) instrument using CDCl 3 as internal standard. Chemical shifts are given in ppm, coupling constants (J) are given in hertz (Hz). IR spectra were recorded on a Nicolet Avatar 320 FT-IR spectrophotometer and are reported in wavenumbers (cm-1). Mass spectra were recorded on a PE Sciex API 2000 triplequadrupole mass spectrometer equipped with a Turbo Ion Spray source and Waters Quattro Micro triple quadrupole mass spectrometer (Manchester, UK). For column chromatography, Merck Silica gel 60 was employed. Enantiomer ratios were determined by a chiral HPLC analysis on a Waters 600 with Waters 996 Photodiode Array Detector using Chiracel OD or OJ column (0.46×25 cm). The product purity was also determined by GC analysis using Agilent 6850 with HP-5 column (30 m×0.25 mm×0.25 µm). Elemental analyses were performed on the Vario EL III. For product sublimation Büchi Glass Oven B-585 was used. Materials. Trimethyl borate, 3-Acetylpyridine (5d) and C-18 reverse phase silica gel (DSC-18 SPE cartridge 0.5 grams) were purchased from Aldrich. The nonstabilizated BH 3 •THF 1.0 M in THF and BH 3 •DMS were obtained from Fluka. LiCl was purchased from Riedel-de-Haën. Fluorous reverse phase silica gel (FluoroFlash TM SPE cartridge 2 grams, 8 ccm tube) was purchased from Fluorous Technologies Inc. THF and diethylether were distilled from sodium/benzophenone prior to use. Corundum (EKF-100) was obtained from MOTIM Ltd. Diphenyl-prolinols IIa, 2 were prepared as described in the literature. 1 Diaryl prolinols 3 2 and 4 3 are known compounds, but we modified their synthesis, so their synthetic intermediates are novel compounds.
Chemical Communications, 2007
General Methods. Difluoroenol silyl ethers 1 2a-2e and monofluoro silyl enol ether 2 4 were prepared as described previously. Tri-n-butyltin fluoride and a 1M toluene solution of P(t-Bu)3, were purchased from Aldrich Chemical Co. and used as received. Toluene was distilled under nitrogen over sodium prior to use. All other chemicals were used as received from commercial sources. 1 H NMR spectra were obtained on a 300-or 500-MHz spectrometer, and chemical shifts were recorded relative to a residual protonated solvent. 13 C NMR spectra were obtained at 75.5 MHz on a 300-MHz instrument, and chemical shifts were recorded relative to the solvent resonance. Both 1 H NMR and 13 C NMR chemical shifts are reported in parts per million relative to tetramethylsilane. 19 F NMR chemical shifts are reported in parts per million from CFCl 3. The solvent was CDCl 3 unless otherwise stated. The purity of products was determined by CH&N elemental analyses. Column chromatography was carried out using ACROS silicagel (0.060-0.200 mm). Thin layer chromatography (TLC) was carried out on commercially available pre-coated plates (Whatman UV 254 silica).
New Direct 11 B NMR-Based Analysis of Organoboranes through Their Potassium Borohydrides
The Journal of Organic Chemistry
Representative organoborane mixtures were quantitatively converted to their borohydrides through their reaction with activated KH (KH*), permitting their detailed analysis by 11 B NMR. Through the treatment of commercial KH with a THF solution of lithium aluminum hydride (LAH), a dramatic change in the surface morphology results as revealed by scanning electron microscopy (SEM). Energy dispersed spectroscopy (EDS) was employed to reveal that the LAH treatment deposits a significant amount of an unknown aluminum-containing species on the surface of the KH, which imparts a unique reactivity to the KH*. Even highly hindered organoboranes are quantitatively converted to their borohydrides by replacing electronegative groups (e.g., OR, halogen) with hydrogen, retaining only the carbon ligation. Through this simple KH* treatment, complex organoborane reaction mixtures are converted to the corresponding borohydrides whose 11 B NMR spectra normally exhibit resolved signals for the individual species present. The integration of these signals provides quantitative information on the relative amounts of each component of the mixture. New generalities for the effect of R- ,-, and γ-substituents have also been determined that provide a new, simple technique for the determination of the isomeric distribution in organoborane mixtures resulting from common organoborane processes (e.g., hydroboration). Moreover, the 1 H-coupled 11 B NMR spectra of these mixtures reveal the extent of alkylation for each species present. Representative organoboranes were examined by this new technique permitting a simple and convenient quantitative analysis of the regio-and diastereomeric composition of a variety of asymmetric organoborane processes. Previously unknown details of pinene-based hydroborations and reductions are revealed for the first time employing the KH* 11 B NMR technique. The widespread use of organoboranes in chemical synthesis provides a clear need for the development of new, more convenient analytical methods for assessing the composition of the intermediates formed in a wide variety of organoborane processes. 1,2 Commonly, 11 B NMR is employed to determine the extent of alkylation, 1,2,4 but the isomeric composition of the organoboranes cannot be directly assessed because of the broad overlapping signals observed. On occasion, organoborane derivatives can be prepared and analyzed by NMR 2,5,6 or by chromatogra-* To whom correspondence should be addressed.
Tetrahedron, 1999
Cyclic and acyclic ~-ketoesters 4, a typical cyclic ct-diketone 5 and a typical cyclic [~-diketone 6 were converted to the corresponding vinyl nonaflates of general formula 7, 8 and 9, respectively, by reaction with 1.2-1.5 equiv of Nail in DMF at 20-55 °C followed by treatment with 1.15-1.30 equiv of perfluoro-l-butanesulfonyl fluoride at 20 °C. These vinyl nonaflates, which were purified by MPLC on silica gel, proved to be excellent electrophiles in Pal-catalyzed cross-coupling reactions with aryl-, l-alkynyl-and alkylzinc chlorides. A variety of cyclic and acyclic tetrasubstituted c~,l~-unsaturated esters which included stereoisomerically pure compounds, a 2substituted 3-aryi-2-cyclopentenone and naturally-occurring dihydrojasmone were cleanly synthesized by these smooth and selective cross-coupling reactions.
Chirality, 2014
Recently, the direct substitution of allylic, benzylic, and tertiary alcohols has been achieved via S N 1-type reactions with catalytic amounts of Brønsted or Lewis acids. When a new stereogenic center is formed most of these transformations produce the desired product as a racemate, as these reactions proceed through carbenium ions. The arsenal of activation modes available in organocatalysis can be used to set up suitable reaction conditions in which chiral nucleophiles (enamine catalysis) or chiral electrophiles (iminium catalysis, chiral counterion catalysis) can easily be generated. Recently, we have used stabilized carbenium ions, directly available or obtained from the corresponding alcohols, in new organocatalytic stereoselective S N 1-type reactions. The commercially available carbenium ion benzodithiolylium tetrafluoroborate 1 can be used for the straightforward organocatalytic stereoselective alkylation of aldehydes. In this account we will illustrate the application of this methodology in the total synthesis of natural products and the preparation of valuable starting materials. Chirality 26:607-613, 2014.
Vanadyl Species Catalyzed 1,2-Oxidative Trifluoromethylation of Unactivated Olefins
ACS Catalysis
C) spectrometers in deuterochloroform with chloroform as an internal reference unless otherwise stated. Chemical shifts are reported in ppm (δ), coupling constants, J, are reported in Hz. The abbreviations s, d, t, pent, quint, sext, dd, ddd, dt, and m stand for the resonance multiplicities singlet, doublet, triplet, pentet, quintet, sextet, doublet of doublets, doublet of doublet of doublets, doublet of triplets, and multiplet, respectively. Mass spectra were recorded with an ionization voltage of 70 or 20 eV unless otherwise stated. HR-EI (High resolution electron ionization) were recorded on JEOL JMS-700. Fast atom bombardment (FAB) and electrospray ionization (ESI) mass spectra were recorded with data reported in the form m/e (intensity relative to base peak). Analytical TLC was performed on Merck silica gel plates with F-254 indicator. Visualization was accomplished with UV light (254 nm) or with phosphomolybdic acid (PMA), DNP, and KMnO 4 staining agents. Column (flash) chromatography was performed by using 230-240 mesh (40-60 m) ATSM MERK silica gel. Analytical high pressure liquid chromatography (HPLC) was performed with a built-in photometric detector ( = 220 nm or 254 nm) using a Diacel ASH , AD-H (0.46 cm 25cm). Solvents for HPLC analyses were of spectroscopic grade and filtered before use. Solvents for extraction and chromatography were reagent grade. Toluene, Tetrahydrofuran (THF) and 1,2-Dimethoxyethane (DME) were dried over sodium benzophenone-ketyl intermediate under N 2 atmosphere and distilled before use. Dichloromethane (DCM) were dried over CaH 2. All reaction products were isolated as 1 b TMSCN 24 trace. 2 c TMSCN 20 80 S4 3 d TMSCN 24 66 4 c TMSOAc 36 68 5 d TBHP in decane 48 67 6 d TBHP in water 48 65 7 c Acetic anhydride 48 46 8 c,e Acetic anhydride 96 55 9 c,f Acetic anhydride 48 47 General procedure for preparation procedures and analytical data for oxidovanadium(V) catalyst 2a, 2b, and 2c. To a solution of 3,5-di-tert-butyl-2-hydroxybenzaldehyde (1217 mg, 5.0 mmol, 1.0 equiv) in MeOH (12.5 mL) was added L-tert-leucine (721 mg, 5.5 mmol, 1.1 equiv) and NaOAc (902 mg, 11.0 mmol, 2.2 equiv). After having been stirred at 80 C for 18 hours, the reaction mixture was gradually cooled to ambient temperature and a solution of VOSO 4 .5H 2 O (1392 mg, 5.5 mmol, 1.1 equiv) in MeOH (5.0 mL) was added. After having been stirred for another 6 h at ambient temperature, the reaction mixture was concentrated under reduced pressure. The resulting dark black solid was washed with water (5 × 30 mL) and dried in vacuo to furnish a crude oxidovanadium(IV) catalyst.
Die Anwendungen von fluorinierten Arylboronaten in der organischen Synthese
2020
Fluorinated compounds are an important motif, particularly in pharmaceuticals, as one-third of the top performing drugs have fluorine in their structures. Fluorinated biaryls also have numerous applications in areas such as material science, agriculture, crystal engineering, supramolecular chemistry, etc. Thus, the development of new synthetic routes to fluorinated chemical compounds is an important area of current research. One promising method is the borylation of suitable precursors to generate fluorinated aryl boronates as versatile building blocks for organic synthesis. Chapter 1 In this chapter, the latest developments in the synthesis, stability issues, and applications of fluorinated aryl boronates in organic synthesis are reviewed. The catalytic synthesis of fluorinated aryl boronates using different methods, such as C–H, C–F, and C–X (X = Cl, Br, I, OTf) borylations are discussed. Further studies covering instability issues of the fluorinated boronate derivatives, which ar...