The catalytic addition of water to alkynes (hydration) generates valuable carbonyl compounds from unsaturated hydrocarbon precursors. Traditional mercury(II) catalysts hydrate terminal with Markovnikov selectivity methyl ketones. Much research has been devoted finding based on less toxic metals, the most promising being gold(I), gold(III), platinum(II), and palladium(II). Catalytic anti-Markovnikov hydration aldehydes realized in an efficient manner ruthenium(II) complex catalysts. present...

The generation of a hidden Brønsted acid as true catalytic species in hydroalkoxylation reactions from metal precatalysts has been clarified case studies. mechanism triflic (CF(3)SO(3)H or HOTf) starting either AgOTf 1,2-dichloroethane (DCE) Cp*RuCl(2)/AgOTf/phosphane combination toluene elucidated. deliberate and controlled HOTf cocatalytic amounts tert-butyl chloride the cold DCE at elevated temperatures results catalyst useful for mechanistic control experiments synthetic applications.

Isolated and crystallized [Ti(TADDOLato)] complexes were used as catalysts for the first catalytic enantioselective (up to 90 % ee) C−F bond-forming reaction, fluorination of β-ketoesters with N-fluorotriethylenediammonium salt F-TEDA [Eq. (1)]. TADDOL=2,2-dimethyl-α,α,α′,α′-tetraaryl-1,3-dioxolan-4,5-dimethanol.

The 1,3-diaryl-imidazolium chlorides IPr.HCl (aryl = 2,6-diisopropylphenyl), IMes.HCl 2,4,6-trimethylphenyl) and IXy.HCl 2,6-dimethylphenyl), precursors to widely used N-heterocyclic carbene (NHC) ligands catalysts, were prepared in high yields (81%, 69% 89%, respectively) by the reaction of 1,4-diaryl-1, 4-diazabutadienes, paraformaldehyde chlorotrimethylsilane dilute ethyl acetate solution. A mechanism involving a 1,5-dipolar electrocyclization is proposed.

The highest enantioselectivity yet for a hydroboration (98% ee) was achieved with the ferrocenyl ligand 1, R1 = R3 Me, R2 H, Ar 4CF3C6H4, in Rh-catalyzed reaction of styrene catecholborane. influence substituents on both pyrazolyl and phosphano fragments studied, observations tentatively interpreted terms varying electronic asymmetry they engender at metal center.

The Ti(TADDOLato) complexes dichloro[(4R,5R)-2,2-dimethyl-α,α,α′,α′-tetraphenyl-1,3-dioxolane-4,5-dimethanolato(2−)-O,O′]titanium ((R)-1a) and dichloro[(4R,5R)-2,2-dimethyl-α,α,α′,α′-tetra(naphthalen-1-yl)-1,3-dioxolane-4,5-dimethanolato(2−)-O,O′]titanium ((R)-1b) are efficient catalysts for the electrophilic enantioselective chlorination bromination of β-keto esters with N-chlorosuccinimide (NCS) N-bromosuccinimide (NBS), respectively. With 5 mol-% catalyst at room temperature an...

Isolierte und kristallisierte [Ti(TADDOLato)]-Komplexe dienen als Katalysatoren für die erste katalytische enantioselektive (bis zu 90 % ee) C-F-Verknüpfung: Fluorierung von β-Ketoestern mit dem N-Fluortriethylendiammmonium-Salz F-TEDA [Gl. (1)]. TADDOL=2,2-Dimethyl-α,α,α′,α′-Tetraaryl-1,3-dioxolan-4,5-dimethanol.

β-Ketoesters can be effectively monofluorinated with F-TEDA using CpTiCl3 as a catalyst. With the use of this catalyst, extent competing difluorination does not reach 10%. [TiCl2(TADDOLato)] complexes catalyze one-pot enantioselective heterodihalogenation β-ketoesters and NCS to afford α-chloro-α-fluoro-β-ketoesters in moderate good yields. The sequence addition halogenating agents determines sense chiral induction.

The anti-Markovnikov hydration of terminal alkynes to give aldehydes is catalyzed by complexes derived in situ from air-stable [CpRu(η6-naphthalene)]PF6 (C) and 6-aryl-2-diphenylphosphinopyridines (L). Ligands L are readily available a modular synthesis. Increasing the size ligand C-6 aryl group order R = Ph < mesityl 2,4,6-triisopropylphenyl (2,4,6-triphenyl)phenyl gave catalysts highest known activity.

The catalytic activity of [CpRu(L)(2)(MeCN)]PF(6) (L = 2-diphenylphosphinopyridine with bulky groups at C-6) for anti-Markovnikov hydration terminal alkynes to aldehydes is retained when one heterocyclic ligand L replaced by L' PPh(3). Equal amounts CpRuCl(PPh(3))(2) (1) and phosphane in acetone solution equilibrate a mixture 1, CpRuCl(L)(PPh(3)) (2), CpRuCl(L)(2) (3), which acts as highly active situ catalyst preparative water-rich media (2 mol % [Ru], 60 °C, 3-18 h 4:1 (v/v)...

Multienzymatic cascades are responsible for the biosynthesis of natural products and represent a source inspiration synthetic chemists. The Fe(II)/α-ketoglutarate-dependent dioxygenase AsqJ from Aspergillus nidulans is outstanding because it stereoselectively catalyzes both ferryl-induced desaturation reaction epoxidation on benzodiazepinedione. Interestingly, enzymatically formed spiro epoxide spring-loads 6,7-bicyclic skeleton non-enzymatic rearrangement into 6,6-bicyclic scaffold...

The first systematic steady-state and time-resolved emission study of firefly oxyluciferin (emitter in bioluminescence) its analogues aqueous buffers provided the individual spectra all chemical forms emitter excited-state equilibrium constants strongly polar environment with strong hydrogen bonding potential. results confirmed earlier hypothesis that proton transfer from enol group is favored over phenol group. In water, phenol-keto form strongest photoacid among isomers conjugate base...

The family of AZARYPHOS (aza-aryl-phosphane) phosphane ligands, containing a phosphine unit and sterically shielded nitrogen lone pairs in the ligand periphery, is introduced as tool for developing ambifunctional catalysis by metal center sphere. General synthetic strategies have been developed to synthesize over 25 examples structurally diverse (6-aryl-2-pyridyl)phosphanes (ARPYPHOS), (6-alkyl-2-pyridyl)phosphanes (ALPYPHOS), 4,6-disubsituted 1,3-diazin-2-ylphosphanes or...

Bulky heterocycles: A highly selective catalytic cross-coupling reaction of tertiary Grignard reagents with chloroazacycles provides a shortcut to heterocyclic building blocks for applications in pharmaceutical chemistry and supramolecular chemistry, or as ligand precursors transition-metal catalysis (see scheme). Supporting information this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2008/z803312_s.pdf from author. Please note: The publisher not...

The mysterious flashes of light communicated by fireflies conceal a rich and exciting solution spectrochemistry that revolves around the chemiexcitation photodecay fluorophore, oxyluciferin. A triple chemical equilibrium double deprotonation keto–enol tautomerism turns this simple molecule into an intricate case where relative spectral contributions six species combine over physiologically relevant pH range, rendering physical isolation characterization most unmanageable. To disentangle...

A complete understanding of the physics underlying varied colors firefly bioluminescence remains elusive because it is difficult to disentangle different enzyme-lumophore interactions. Experiments on isolated ions are useful establish a proper reference when there no microenvironmental perturbations. Here, we use action spectroscopy compare absorption by oxyluciferin lumophore in vacuo and complexed with single water molecule. While process relevant within luciferase cavity light emission,...

Abstract The asymmetric cyclization of 2′‐hydroxychalcones to flavanones is a basic, enzyme‐catalyzed step in the biosynthesis flavonoid natural products, but poses long‐standing problem for catalysis with small molecule catalysts. Earlier claims concerning realization an flavanone synthesis by means camphorsulfonic acid as chiral Brønsted catalysts were reinvestigated using accurate HPLC methods quantification enantiomer ratios. previous induction thus shown be untenable. On other hand,...

Stereocontrolled access to the hexacyclic core of FD-594 has been achieved. The key steps include intramolecular S(N)Ar reaction for construction densely functionalized xanthone skeleton, stereoselective lactone cleavage using a chiral nucleophile induce axial stereochemistry, and SmI(2)-mediated pinacol cyclization stereocontrolled conversion axially biaryl dialdehyde into corresponding trans diol.

Abstract The substrate range of the [TiCl 2 (TADDOLate)] (TADDOL= α , ′, ′‐tetraaryl‐1,3‐dioxolane‐4,5‐dimethanol)‐catalyzed asymmetric ‐fluorination activated β ‐carbonyl compounds has been investigated. Optimal conditions for catalysis are characterized by using 5 mol‐% TiCl (naphthalen‐1‐yl)‐TADDOLate) as catalyst in a saturated (0.14 mol/l) MeCN solution F‐TEDA (1‐(chloromethyl)‐4‐fluoro‐1,4‐diazoniabicyclo[2.2.2]octane bis‐[tetrafluoroborate]) at room temperature. A series ‐methylated...

Abstract The asymmetric catalytic cyclization of the simple 2′‐hydroxychalcone ( 1 ) to flavanone 2 ), a model for chalcone isomerase reaction, has been realized as ion‐pairing process with chiral quaternary ammonium salts (e.g., 9‐anthracenylmethlycinchoninium chloride; 9‐Am‐CN‐Cl) and NaH small‐molecule co‐catalyst. In toluene/CHCl 3 solution, reaches an intrinsic enantioselectivity up S = 14.4 er 93.5:6.5). reversible reaction proceeds in two steps: A fast initial approaches...

Abstract The asymmetric catalytic addition of alcohols (phenols) to non‐activated alkenes has been realized through the cycloisomerization 2‐allylphenols 2‐methyl‐2,3‐dihydrobenzofurans (2‐methylcoumarans). reaction was catalyzed by a chiral titanium–carboxylate complex at uncommonly high temperatures for reactions. catalyst generated mixing titanium isopropoxide, ligand ( aS )‐1‐(2‐methoxy‐1‐naphthyl)‐2‐naphthoic acid or its derivatives, and co‐catalytic amount water in ratio 1:1:1 (5 mol %...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis and Structure of Pyrazole-Containing Ferrocenyl Ligands for Asymmetric CatalysisUrs Burckhardt, Lukas Hintermann, Anita Schnyder, Antonio TogniCite this: Organometallics 1995, 14, 11, 5415–5425Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://pubs.acs.org/doi/10.1021/om00011a069https://doi.org/10.1021/om00011a069research-articleACS PublicationsRequest reuse...

Abstract The complex cations [M(η 3 ‐R 2 All)(PPFPz{3‐ t Bu})] + (M = Pd II , R All 1,3‐diphenylallyl, 1,3‐dicyclohexylallyl, indenyl; M Pt 1,3‐diphenylallyl; PPFPz‐{3‐ Bu} 3‐ tert ‐butyl‐1‐{1‐[2‐diphenylphosphanyl‐ferrocenyl]ethyl}‐1 H ‐pyrazole)have been prepared as salts with PF 6 – or SbF . They have characterized by NMR spectroscopy in solution and X‐ray crystallography the solid state. Their reactions sources of nucleophilic “naked” fluoride investigated multinuclear spectroscopy....

Cinchona alkaloids catalyze the oxa-Michael cyclization of 4-(2-hydroxyphenyl)-2-butenoates to benzo-2,3-dihydrofuran-2-yl acetates and related substrates in up 99% yield 91% ee (ee = enantiomeric excess). Catalyst substrate variation studies reveal an important role alkaloid hydroxy group reaction mechanism, but not sense a hydrogen-bonding activation carbonyl as assumed by Hiemstra-Wynberg mechanism bifunctional catalysis. Deuterium labeling at C-2 shows that addition RO-H alkenoate occurs...