An alternative route to synthesise alkenes, based only on the KOtBu/DMF promoted activation and direct coupling of alcohols with phenyl acetonitriles, is reported. Various E‐stilbenes have thus been ...obtained directly from alcohols that are sustainable sources of carbon, which to our knowledge, is unprecedented in the absence of transition metal based catalysts. A variation allowing, through a Csp3−Csp3 bond formation, the selective synthesis of N‐Heteroarenes is also described. A mechanism for the olefination pathway proceeding via an original activation of alcohols under alkyl formates is provided.
A new route to E‐Stilbenes, based on the transition metal free, KOtBu/DMF promoted activation and direct coupling of alcohols with phenyl acetonitriles, is reported. A variation allowing the selective synthesis of N‐Heteroarenes and a mechanism proceeding via the activation of alcohols under alkyl formate intermediates are also reported.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A new family of carbon‐bound boron enolates, generated by a kinetically controlled halogen exchange between chlorocatecholborane and silylketene acetals, is described. These C−boron enolates are ...demonstrated to activate 1,3‐enyne substrates in the presence of a Pd0/Senphos ligand complex, resulting in the first examples of a carboboration reaction of an alkyne with enolate‐equivalent nucleophiles. Highly substituted dienyl boron building blocks are produced in excellent site‐, regio‐, and diastereoselectivity by the described catalytic cis‐carboboration reaction.
A new family of carbon‐bound boron enolates, in cooperation with a Pd complex supported by an 1,4‐azaborine‐derived phosphine ligand, transforms enynes into highly substituted dienyl boronates in exquisite site‐, regio‐, and cis‐diastereoselectivity.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The long‐standing quest for chiral hypervalent organoiodine compounds (i.e., iodanes) as metal‐free reagents for asymmetric synthesis continues. Although remarkable progress has recently been made in ...organoiodine‐catalyzed reactions using a terminal oxidant in stoichiometric amounts, there is still a significant need for “flaskable” chiral iodane reagents. Herein, we describe the synthesis of new iodobinaphthyls and iodobiphenyls, their successful and selective DMDO‐mediated oxidation into either λ3‐ or λ5‐iodanes, and the evaluation of their capacity to promote asymmetric hydroxylative phenol dearomatization (HPD) reactions. Most notably, a C2‐symmetrical biphenylic λ5‐iodane promoted the HPD‐induced conversion of the monoterpene thymol into the corresponding ortho‐quinol‐based 4+2 cyclodimer (i.e., bis(thymol)) with enantiomeric excesses of up to 94 %.
The selective oxygenation of iodobinaphthyls and iodobiphenyls afforded either λ3‐ or λ5‐iodanes, which were evaluated for their capacity to promote asymmetric intermolecular hydroxylative phenol dearomatizations (HPDs). Most remarkably, a C2‐symmetrical biphenylic λ5‐iodane induced the HPD reaction/4+2 cyclodimerization cascade of thymol into bis(thymol) with enantiomeric excesses of up to 94 %.
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The Matsuda‐Heck reaction, usually performed with palladium catalysts, can be carried out under transition‐metal‐free conditions in the presence of a KOtBu/DMF couple. This system allows the ...selective and direct synthesis of stilbenes from aryldiazonium salts under mild temperature (20 °C). Mechanistic studies suggest a radical pathway in which the DMF acts as the initiator of the overall process.
The Matsuda‐Heck reaction is carried out under transition metal free conditions in the presence the KOtBu/DMF system which allows, at 20 °C, the selective and direct synthesis of stilbenes from aryldiazonium salts. Mechanistic studies suggest an overall radical process.
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The first example of an enantioselective carbocyclization of an alkyne‐containing substrate catalyzed by chiral Brønsted acids was achieved. The use of the 2‐hydroxynaphthyl substituent on the alkyne ...as a directing group constituted the key parameter enabling both efficient regioselective protonation of the carbon–carbon triple bond and chiral induction. The key cationic intermediate could be depicted either as a cationic vinylidene ortho‐quinone methide or a stabilized vinyl cation. Atropoisomeric phenanthrenes derivatives were produced in high yields and good enantioselectivities under mild, metal‐free reaction conditions in the presence of chiral N‐triflylphosphoramide catalysts. The carbenic nature of the cationic intermediate was also exploited to describe an example of alkyne/alkane cycloisomerization.
Chiral N‐triflyl phosphoramides catalyze the asymmetric carbocyclization of alkynyl aryl substrates. The introduction of a 2‐naphtolyl substituent on the alkyne enables the chemo‐ and regioselective protonation of alkynes and delivers atropisomeric phenanthrenes and dihydronaphtalenes enantioselectively.
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Rationale
The concentrations of aldehydes and volatile fatty acids have to be controlled because of their potential harmfulness in indoor air or relationship with the organoleptic properties of ...agri‐food products. Although several specific analytical methods are currently used, the simultaneous analysis of these compounds in a complex matrix remains a challenge. The combination of positive and negative ionization selected ion flow tube mass spectrometry (SIFT‐MS) allows the accurate, sensitive and high‐frequency analysis of complex gas mixtures of these compounds.
Methods
The ion–molecule reactions of negative precursor ions (OH−, O•−, O2•−, NO2− and NO3−) with five aldehydes and four carboxylic acids were investigated in order to provide product ions and rate constants for the quantification of these compounds by negative ion SIFT‐MS. The results were compared with those obtained by conventional analysis methods and/or with already implemented SIFT‐MS positive ionization methods. The modelling of hydroxide ion (OH−)/molecule reaction paths by ab‐initio calculation allowed a better understanding of these gas‐phase reactions.
Results
Deprotonation systematically occurs by reaction between negative ions and aldehydes or acids, leading to the formation of M − H− primary ions. Ab‐initio calculations demonstrated the α‐CH deprotonation of aldehydes and the acidic proton ion for fatty acids. For aldehydes, the presence of water in the flow tube leads to the formation of hydrated ions, M − H−.H2O. With the NO2− precursor ion, a second reaction channel results in ion–molecule association with the formation of M.NO2− ions.
Conclusions
Except for formaldehyde, all the studied compounds can be quantified by negative ion SIFT‐MS with significant rate constants. In addition to positive ion SIFT‐MS with H3O+, O2+ and NO+ precursor ions, negative ionization with O•−, O2•−, OH−, NO2− and NO3− extends the range of analysis of aldehydes and carboxylic acids in air without a preparation or separation step. This methodology was illustrated by the simultaneous quantification in single‐scan experiments of seven aldehydes and six carboxylic acids released by building materials.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
An alternative route to synthesise alkenes, based only on the KO
t
Bu/DMF promoted activation and direct coupling of alcohols with phenyl acetonitriles, is reported. Various
E
‐stilbenes ...have thus been obtained directly from alcohols that are sustainable sources of carbon, which to our knowledge, is unprecedented in the absence of transition metal based catalysts. A variation allowing, through a Csp
3
−Csp
3
bond formation, the selective synthesis of
N
‐Heteroarenes is also described. A mechanism for the olefination pathway proceeding via an original activation of alcohols under alkyl formates is provided.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Ortho‐alkynyl biaryls react in the presence of catalytic amount of Brønsted acids to give phenanthrenes in high yields under mild conditions. The activity and selectivity of this transformation are ...governed by the substitution pattern of the diarylalkyne moiety. Selectivity shifts are observed between the carbophilic Lewis and Brønsted acid‐catalyzed cycloisomerization involving alkyne activation.
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Anion metathesis of imidazol(in)ium chlorides with KHCO3 afforded an easy one step access to air stable imidazol(in)ium hydrogen carbonates, denoted as NHC(H)HCO3. In solution, these compounds ...were found to be in equilibrium with their corresponding imidazol(in)ium carboxylates, referred to as N-heterocyclic carbene (NHC)-CO2 adducts. The NHC(H)HCO3 salts were next shown to behave as masked NHCs, allowing for the NHC moiety to be readily transferred to both organic and organometallic substrates, without the need for dry and oxygen-free conditions. In addition, such NHC(H)HCO3 precursors were successfully investigated as precatalysts in two selected organocatalyzed reactions of molecular chemistry and polymer synthesis, namely, the benzoin condensation reaction and the ring-opening polymerization of d,l-lactide, respectively. The generation of NHCs from NHC(H)HCO3 precursors occurred via the formal loss of H2CO3 via a concerted low energy pathway, as substantiated by Density Functional Theory (DFT) calculations.
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IJS, KILJ, NUK, PNG, UL, UM
This article explores the contrasting reactivity of cyclopropyl complexes of early transition metals. Cp*W(NO)(CH2R)(c‐C3H5) (R = SiMe3, Ph, t‐Bu) generated in THF solution from Cp*W(NO)(CH2R)Cl and ...Mg(c‐C3H5)2(dioxane)x readily rearrange to η3‐allyl derivatives Cp*W(NO)(CH2R)(η3‐C3H5) by an intramolecular ring opening reaction. Both direct and catalyzed pathways are revealed by kinetic studies. Computational modeling indicates the ring opening reaction is preferred on thermodynamic grounds for tungsten whereas kinetic products arising from β‐H ion reactions of cyclopropane are observed for related zirconium and niobium complexes reported previously. The energetic accessibility and the nature of the LUMO in the tungsten complexes promote distal CC bond cleavage in the cyclopropyl ring.
In situ generated alkyl cyclopropyl complexes of tungsten readily rearrange to η3‐allyl complexes thanks to an easily accessible LUMO which favors distal CC bond cleavage in contrast to cyclopropane elimination observed for zirconium and niobium analogues.
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