The stereoselective formation of C-C bonds is great importance for the synthesis enantiomerically pure natural products and pharmaceuticals. A broad repertoire chiral auxiliaries, reagents, catalysts can be utilized reliable generation tertiary stereocenters. In contrast, organic compounds with quaternary stereocenters a much more demanding challenging task. Every enantioselective synthetic method demonstrate its value through fully substituted carbon center. this Minireview examples newer...

Abstract Quaternary stereocenters are a particular challenge for stereoselective synthesis. With central view on this specific structural issue, selected examples from the recent literature highlighted in order to evaluate state of art asymmetric CC bond formation. The review is divided into sections addition and substitution reactions, rearrangements cycloaddition reactions.

PdII-catalyzed Michael reactions of β-dicarbonyl compounds 1 and enones 2 can generate quaternary stereocenters (shown in yellow) with selectivities 90 % ee at relatively high temperatures (−10 °C). This method represents a breakthrough enantioselective synthesis.

The conjugate addition of carbon nucleophiles to acceptor activated olefins is one the most important reactions for carbon-carbon bond formation. With optically active metal complexes this transformation can be catalyzed enantioselectively. This review a collection newer literature (since 2001) on topic. salts and applied are in broad range, starting from solely Lewis acidic M(II) M(III) compounds, such as magnesium, zinc, boron, aluminum lanthanoids. Transition-metal catalysts suitable...

The efficient conversion of light into electricity or chemical fuels is a fundamental challenge. In artificial photosynthetic and photovoltaic devices, this generally thought to happen on ultrafast, femto-to-picosecond timescales involve an incoherent electron transfer process. some biological systems, however, there growing evidence that the coherent motion electronic wavepackets essential primary step, raising questions about role quantum coherence in devices. Here we investigate...

Die stereoselektive Knüpfung von C-C-Bindungen ist zentraler Bedeutung für die Synthese enantiomerenreiner Natur- und Wirkstoffe. Dank eines großen Arsenals chiraler Auxiliare, Reagentien Katalysatoren der Aufbau tertiärer Stereozentren in Regel mit hoher Zuverlässigkeit möglich. Dagegen komplexer Moleküle quartären eine wesentlich anspruchsvollere Aufgabe. Jede enantioselektive Synthesemethode demonstriert ihren Wert, wenn es um den dieser vollständig substituierten Kohlenstoffzentren geht....

Transition-metal catalysis of the Michael reaction 1,3-dicarbonyl compounds with acceptor-activated alkenes is introduced as a valuable alternative to classic base this reaction. Owing mild, neutral conditions, chemoselectivity these processes superior that offered by catalysis, since latter suffers from various unwanted side- and subsequent reactions, such aldol cyclizations ester solvolyses. The most efficient transition-metal catalysts do not require inert or anhydrous even solvents are...

Durch PdII katalysierte Michael-Reaktionen zwischen β-Dicarbonylen 1 und Enonen 2 können quartäre Stereozentren (gelb unterlegt) mit Selektivitäten von 90 % ee bei relativ hohen Temperaturen (−10 °C) aufgebaut werden. Damit ist ein Durchbruch der enantioselektiven Synthese gelungen.

Abstract The most convenient and direct route to α‐hydroxy‐β‐dicarbonyl compounds is the oxidation of readily accessible 1,3‐dicarbonyls. Hence, this type an intensively investigated field. In short review, we present compare α‐hydroxylations using various oxidants such as peracids (Rubottom oxidation), dimethyldioxirane or molecular oxygen. From economical ecological point view, metal‐catalyzed air oxidations are optimal at least for cyclic β‐dicarbonyls. For asymmetric only chiral...

Iron(III) chloride hexahydrate catalyses the Michael reaction of 1,3-dicarbonyl compounds with α,β-unsaturated ketones under mild and neutral conditions extraordinary efficiency. The chemoselectivity this FeIII-catalysed process is superior to that classic base-catalysed reaction, since latter suffers from various side reactions, namely drawbacks such as aldol cyclisations ester solvolysis. Excellent yields chemoselectivities together environmentally friendly nature FeIII catalysis makes an...

Abstract We report the metal‐catalyzed α‐hydroxylation of a variety cyclic and acyclic β‐dicarbonyl compounds by molecular oxygen. The decisive advantage this new method is use catalytic amounts nontoxic cerium salt CeCl 3 ·7H 2 O in 2‐propanol at ambient temperature. Most substrates 4a − 4i give high yields analytically pure products 5a 5i , workup procedure simple filtration through silica gel. oxidation dicarbonyl 4j 4p however, accompanied side reactions decomposition, reducing 5j 5p...

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTCatalytic Dimerization Reactions of α-Olefins and α,ω-Dienes with Cp2ZrCl2/Poly(methylalumoxane): Formation Dimers, Carbocycles, OligomersJens Christoffers Robert G. BergmanView Author Information Department Chemistry, University California Berkeley, 94720 Cite this: J. Am. Chem. Soc. 1996, 118, 19, 4715–4716Publication Date (Web):May 15, 1996Publication History Received23 January 1996Published online15 May inissue 1...

Ferric chloride hexahydrate catalyzes the Michael reaction of 1,3-dicarbonyl compounds with α,β-unsaturated ketones under mild and non-basic conditions extraordinary efficiency. The chemoselectivity this Fe(III)-catalyzed process is superior to that classic base-mediated reaction, since latter suffers from various side subsequent reactions, namely drawbacks such as aldol cyclizations retro-Claisen reactions. Excellent yields chemoselectivities together environmentally friendly nature Fe(III)...

Quaternary stereocenters were constructed with an enantioselectivity of up to 91% ee under aerobic conditions and at ambient temperature in the Michael reaction β-dicarbonyl compounds methyl vinyl ketone Ni(OAc)2·4H2O optically active trans-1,2-diaminocyclohexane as a chiral catalyst.

Convenient and direct: 1,4-Dicarbonyl compounds are readily obtained through a one-pot cerium-catalyzed oxidative CC coupling in the presence of oxygen subsequent fragmentation. The products suitable precursors for heterocycles.

Abstract Cyclic β‐oxo esters are converted with enol acetates in a cerium‐catalyzed, oxidative Umpolung reaction to furnish 1,4‐diketones up 95 % yield. Atmospheric oxygen is the oxidant this process, which can be regarded as ideal from economic and ecological points of view. Further advantages new C–C coupling its operational simplicity application nontoxic inexpensive CeCl 3 · 7H 2 O precatalyst.

Bicyclic diketones and lactones are obtained in up to 60% yield the aerobic, manganese‐catalyzed intramolecular radical cyclization of β‐oxoesters with a six‐membered ring phenyl or diphenyl allyl substituents γ‐position. Intermediate products this transformation peroxides, which processed either reductively zinc–acetic acid by Kornblum‐DeLaMare fragmentation (with acetyl chloride–pyridine). The respective congeners five‐ seven‐membered rings undergo only α‐hydroxylation reactions mixtures...

J. Christoffers, Chem. Commun., 1997, 943 DOI: 10.1039/A700838D

Dialkyl amides of L-valine, L-isoleucine, and L-tert-leucine (2) are excellent chiral auxiliaries for the construction quaternary stereocenters at ambient temperature. Enaminoesters 3, prepared from these 2 Michael donors 1, undergo a copper-catalyzed asymmetric reaction with methyl vinyl ketone (MVK, 4) to afford products 5 in 70-90% yield 90-99% ee (enantiomeric excess). The exclusion moisture or oxygen is not necessary. readily available by standard procedures. After workup they can be...

Extensive investigations of chiral auxiliaries and active metals for Michael addition 1,3-dicarbonyl compounds with vinyl ketones are summarized. Our efforts result in a widely applicable auxiliary-mediated, copper(II) acetate-catalyzed procedure. For these purposes, L-valine diethylamide is an optimal auxiliary giving quaternary stereocenters up to 99 % ee at ambient temperature. No inert or anhydrous conditions required, the solvent simply acetone, can be recovered almost quantitatively...

Abstract A direct route to enantiomerically pure (−)‐kjellmanianone is reported. The synthesis involves a cerium‐catalyzed α‐hydroxylation and an enzyme‐catalyzed procedure resolve tertiary alcohols at key stages. intermediate β‐oxo ester was α‐hydroxylated give good yields of racemic kjellmanianone. resolution the material achieved by enzymatic saponification, followed chemical decarboxylation sequence enantiopure with 99 % ee. Bromination then afforded (−)‐bromo derivative, whose X‐ray...

Abstract p ‐Benzenedisulfonic acid and 1,3,5‐benzenetrisulfonic are prepared in an efficient scalable two‐step protocol from respective bromobenzene derivatives. These acids used analogy to terephthalic trimesic for the formation of metal‐organic frameworks with copper(II) centers. Due enhanced acidity sulfonic acids, weakly basic malachite can be as inorganic precursor material. After dehydration at about 100 °C, anhydrous exhibit significantly increased thermal stability (up 400 °C)...