13 research outputs found
Convergent Synthesis, Resolution, and Chiroptical Properties of Dimethoxychromenoacridinium Ions
Cationic azaoxa[4]Āhelicenes can be
prepared in a single step from
a common xanthenium precursor by addition of nucleophilic amines under
monitored conditions (160 Ā°C, 2 min, MW). The (ā)-(<i>M</i>) and (+)-(<i>P</i>) enantiomers can be separated
by chiral stationary-phase chromatography. Determination of the absolute
configuration and racemization barrier (Ī<i>G</i><sup>ā§§</sup> (433 K) 33.3 Ā± 1.3 kcalĀ·mol<sup>ā1</sup>) was achieved by VCD and ECD spectroscopy, respectively
General Ir-Catalyzed NāH Insertions of Diazomalonates into Aliphatic and Aromatic Amines
A general NāH
insertion reactivity of acceptorāacceptor
diazo malonate reagents is reported using [Ir(cod)Cl]2 as
catalyst. A large range of amines, primary and secondary, aliphatic
and aromatic, is possible. Mild temperatures, perfect substrate/reactant
stoichiometry, and good functional group compatibility render the
process particularly attractive for the (late-stage) functionalization
of amines
One-Step Synthesis of Nitrogen-Containing Medium-Sized Rings via Ī±āImino Diazo Intermediates
Eight- and 9-membered dioxazocines
and dioxazonines are readily
synthesized starting from <i>N</i>-sulfonyl-1,2,3-triazoles
in a single-step procedure. A perfect regioselectivity and generally
good yields (up to 92%) are obtained under dirhodium catalysis using
1,3-dioxolane and 1,3-dioxane as solvents and reagents
Efficient Synthesis of Imino-methano TroĢger Bases by Nitrene Insertions into CāN Bonds
A direct nitrene insertion into CāN bonds is observed upon treatment of <i>methano</i>-TroĢger bases with arylsulfonyl iminophenyliodinanes under copper and dirhodium catalysis. Novel cyclic imino-methano TroĢger bases are obtained (55ā88%). Enantiopure products (<i>ee</i> ā„ 99%) can be obtained with tailored substrates
Efficient Synthesis of Imino-methano TroĢger Bases by Nitrene Insertions into CāN Bonds
A direct nitrene insertion into CāN bonds is observed upon treatment of <i>methano</i>-TroĢger bases with arylsulfonyl iminophenyliodinanes under copper and dirhodium catalysis. Novel cyclic imino-methano TroĢger bases are obtained (55ā88%). Enantiopure products (<i>ee</i> ā„ 99%) can be obtained with tailored substrates
Synthesis, Structural Analysis, and Catalytic Properties of Tetrakis(binaphthyl or octahydrobinaphthyl phosphate) Dirhodium(II,II) Complexes
The X-ray structural analyses of homoleptic RhĀ(II) complexes
made of enantiopure (<i>R</i>)-1,1ā²-binaphthyl and
(<i>R</i>)-(5,5ā²,6,6ā²,7,7ā²,8,8ā²-octahydro)Ābinaphthyl
phosphate ligands are for the first time presented. The possibility
to introduce halogen atoms at the 3,3ā²-positions is also reported.
The isolated dirhodium complexes were further tested as catalysts
(1 mol %) in enantioselective cyclopropanations and SiāH insertion
reactions, affording chiral cyclopropanes and silanes in good yield
but moderate enantioselectivity (ee max 63%)
Kinetics of Rh(II)-Catalyzed Ī±āDiazo-Ī²-ketoester Decomposition and Application to the [3+6+3+6] Synthesis of Macrocycles on a Large Scale and at Low Catalyst Loadings
In the context of [3+6+3+6] macrocyclization
reactions, precise
kinetics of Ī±-diazo-Ī²-ketoester decomposition were measured
by <i>in situ</i> infrared (IR) monitoring. Dirhodium complexes
of IkegamiāHashimoto typeīøand perchlorinated phthalimido
derivatives in particularīøperformed better than classical achiral
complexes. Clear correlations were found between speciation among
dirhodium species and catalytic activity. With these results, novel
cyclohexyl-derived catalysts were developed, affording good yields
of macrocycles (up to 78%), at low catalyst loadings (from 0.01 molāÆ%
to 0.001 molāÆ%) and on a large scale (from 1 g to 20 g)
Bright Electrochemiluminescence Tunable in the Near-Infrared of Chiral Cationic Helicene Chromophores
Cationic
helicenes are <i>ortho</i>-fused polyaromatics
which exhibit well-defined and stable helical conformations with original
absorption and emission properties in the red to near-infrared spectral
ranges. Herein, a selection of cationic [4] and [6]Āhelicenes are studied
for their electrochemical, fluorescence, and electrochemiluminescence
(ECL) properties in acetonitrile solutions. Their photophysical and
redox responses are drastically tuned by the introduction of auxochrome
substituents at their periphery or the interconversion of oxygen and
nitrogen atoms within the helical core. All diaza helicenes exhibit
a reversible reduction process, whereas in the presence of oxygen
instead of nitrogen atoms in the helical core, irreversible oxidations
and a decrease of ECL intensity are observed. ECL emission was successfully
produced with two sacrificial coreactants (benzoyl peroxide and tri-<i>n</i>-propylamine, TPrA). [4]ĀHelicene <b>DMQA</b><sup><b>+</b></sup>, [6]Āhelicene <b>DIAZAĀ(Pr/Br)</b><sup><b>+</b></sup>, and <b>DIAZAĀ(Hex/Br)</b><sup><b>+</b></sup> exhibit similar ECL emission wavelength in the near-infrared
region and generate very intense ECL signals. Their ECL efficiencies
are up to 2.6 times higher than that of the reference compound [RuĀ(bpy)<sub>3</sub>]<sup>2+</sup> when using TPrA as coreactant. A thermodynamic
map gathering both oxidation and reduction potentials and fluorescence
data is proposed for the prediction of energy sufficiency needed in
both coreactant ECL systems. Such a systematic overview based on the
photophysical and electrochemical properties may guide the conception
and synthesis of new chromophores with a strong ECL proficiency
Triple <i>para</i>-Functionalized Cations and Neutral Radicals of Enantiopure Diaza[4]helicenes
Modulation of absorbance and emission is key for the
design of
chiral chromophores. Accessing a series of compounds absorbing and
emitting (circularly polarized) light over a wide spectral window
and often toward near-infrared is of practical value in (chir)optical
applications. Herein, by late-stage functionalization on derivatives
bridging triaryl methyl and helicene domains, we have achieved the
regioselective triple introduction of para electron-donating
or electron-withdrawing substituents. Extended tuning of electronic
(e.g., E1/2red ā1.50
V ā ā0.68 V) and optical (e.g., emission covering from
550 to 850 nm) properties is achieved for the cations and neutral
radicals; the latter compounds being easily prepared by mono electron
reductions under electrochemical or chemical conditions. While luminescence
quantum yields can be increased up to 70% in the cationic series,
strong Cotton effects are obtained for certain radicals at low energies
(Ī»abs ā¼ 700ā900 nm) with gabs values above 10ā3. The open-shell
electronic nature of the radicals was further characterized by electron
paramagnetic resonance revealing an important spin density delocalization
that contributes to their persistence
Triple <i>para</i>-Functionalized Cations and Neutral Radicals of Enantiopure Diaza[4]helicenes
Modulation of absorbance and emission is key for the
design of
chiral chromophores. Accessing a series of compounds absorbing and
emitting (circularly polarized) light over a wide spectral window
and often toward near-infrared is of practical value in (chir)optical
applications. Herein, by late-stage functionalization on derivatives
bridging triaryl methyl and helicene domains, we have achieved the
regioselective triple introduction of para electron-donating
or electron-withdrawing substituents. Extended tuning of electronic
(e.g., E1/2red ā1.50
V ā ā0.68 V) and optical (e.g., emission covering from
550 to 850 nm) properties is achieved for the cations and neutral
radicals; the latter compounds being easily prepared by mono electron
reductions under electrochemical or chemical conditions. While luminescence
quantum yields can be increased up to 70% in the cationic series,
strong Cotton effects are obtained for certain radicals at low energies
(Ī»abs ā¼ 700ā900 nm) with gabs values above 10ā3. The open-shell
electronic nature of the radicals was further characterized by electron
paramagnetic resonance revealing an important spin density delocalization
that contributes to their persistence