Search results for "Intramolecular force"
showing 10 items of 599 documents
Extreme nuclear magnetic resonance: Zero field, single spins, dark matter….
2019
An unusual regime for liquid-state nuclear magnetic resonance (NMR) where the magnetic field strength is so low that the $J$-coupling (intramolecular spin-spin) interactions dominate the spin Hamiltonian opens a new paradigm with applications in spectroscopy, quantum control, and in fundamental-physics experiments, including searches for well-motivated dark-matter candidates. An interesting possibility is to bring this kind of "extreme NMR" together with another one---single nuclear spin detected with a single-spin quantum sensor. This would enable single-molecule $J$-spectroscopy.
A general overview of the organocatalytic intramolecular aza-Michael reaction
2014
The organocatalytic intramolecular aza-Michael reaction gives access to enantiomerically enriched nitrogen-containing heterocycles in a very simple manner. Enals, enones, conjugated esters and nitro olefins have been employed as Michael acceptors, while moderate nitrogen nucleophiles such as sulphonamides, carbamates and amides have been shown to be appropriate Michael donors in this type of reaction. Additionally, the process has been performed under both covalent and non-covalent catalysis, with diaryl prolinols, imidazolidinones, thioureas and chiral binol phosphoric acids being the most frequently used catalysts. The level of efficiency reached with this protocol is demonstrated by the …
Tandem gold self-relay catalysis for the synthesis of 2,3-dihydropyridin-4(1 H)-ones: combination of σ and π Lewis acid properties of gold salts.
2014
The dual ability of gold salts to act as π- and σ Lewis acids has been exploited in a tandem self-relay catalysis. Thus, triphenylphosphanegold(I) triflate mediated the intramolecular carbonyl addition of the amide functionality of homoprogargyl amides to a triple bond. The formation of a σ complex of the gold salt with the intermediate oxazine promoted a nucleophilic addition followed by a Petasis-Ferrier rearrangement. This tandem protocol, catalyzed by the same gold salt under the same reaction conditions, gave rise to the efficient synthesis of 2,3-dihydropyridin-4-(1 H)-ones, which contain a cyclic quaternary α-amino acid unit. The asymmetric version was performed by generating the sta…
1,4-Benzoquinones with Styryl Substituents
2002
2-Styryl-1,4-benzoquinone (1) and compounds 2 and 3 containing 1 as a substructure all proved to be highly reactive towards thermal or photochemical [4π + 2π] cyclodimerization reactions. Chemo-, regio- and stereoselective processes lead to dimers (compounds 1−10), which can undergo secondary reactions consisting of the addition of nucleophiles combined with a twofold keto-enol tautomerism (10 ⇄ 12). An alternative process is dehydrogenation/oxidation followed by an intramolecular [4π + 2π] cycloaddition (10 ⇄ 11). The same selective [4π + 2π] cyclodimerization can be observed in solution upon irradiation (e.g., 1a ⇄ 10a), in contrast to irradiation in the crystalline state which yields a […
Tandem cross enyne metathesis (CEYM)–intramolecular Diels–Alder reaction (IMDAR). An easy entry to linear bicyclic scaffolds
2015
A new tandem cross enyne metathesis (CEYM)–intramolecular Diels–Alder reaction (IMDAR) has been carried out. It involves conjugated ketones, esters or amides bearing a remote olefin and aromatic alkynes as the starting materials. The overall process enables the preparation of a small family of linear bicyclic scaffolds in a very simple manner with moderate to good levels of diastereoselectivity. This methodology constitutes one of the few examples that employ olefins differently than ethylene in tandem CEYM–IMDAR protocols.
ChemInform Abstract: Tandem Cross Enyne Metathesis (CEYM)-Intramolecular Diels-Alder Reaction (IMDAR). An Easy Entry to Linear Bicyclic Scaffolds.
2015
A new tandem cross enyne metathesis (CEYM)–intramolecular Diels–Alder reaction (IMDAR) has been carried out. It involves conjugated ketones, esters or amides bearing a remote olefin and aromatic alkynes as the starting materials. The overall process enables the preparation of a small family of linear bicyclic scaffolds in a very simple manner with moderate to good levels of diastereoselectivity. This methodology constitutes one of the few examples that employ olefins differently than ethylene in tandem CEYM–IMDAR protocols.
Synthesis of 2-isoxazolines: enantioselective and racemic methods based on conjugate additions of oximes.
2010
The formation of 3-unsubstituted 2-isoxazolines by means of condensation reactions between α,β-unsaturated aldehydes and oximes proceeds readily in the presence of catalytic amounts of anilinium salts. Mechanistically, the process involves a fast conjugate addition of the oxime and a slower intramolecular oxime-transfer reaction. The rate of oxime transfer was found to correlate with the acidity of the catalyst. This finding enabled us to discover an enantioselective process in which the fragile conjugate-addition product generated in the first stage is rapidly cyclized into the stable isoxazoline under acidic conditions, with conservation of enantiomeric excess. In summary, herein we descr…
Low-pressure pyrolysis of tBu2SO: synthesis and IR spectroscopic detection of HSOH.
2005
Sulfenic acid (HSOH, 1) has been synthesized in the gas-phase by low-pressure high-temperature (1150 degrees C) pyrolysis of di-tert-butyl sulfoxide (tBu(2)SO, 2) and characterized by means of matrix isolation and gas-phase IR spectroscopy. High-level coupled-cluster (CC) calculations (CCSD(T)/cc-pVTZ and CCSD(T)/cc-pVQZ) support the first identification of the gas-phase IR spectrum of 1 and enable its spectral characterization. Five of the six vibrational fundamentals of matrix-isolated 1 have been assigned, and its rotational-resolved gas-phase IR spectrum provides additional information on the O-H and S-H stretching fundamentals. Investigations of the pyrolysis reaction by mass spectrome…
Synthesis and characterization of monomeric siloxo palladium(II) complexes: crystal structure of [Pd(tmeda)(C6F5)(OSiPh3)]
2004
Abstract Mononuclear palladium-hydroxo complexes of the type [Pd(N–N)(C6F5)(OH)] [(N–N)=2,2′-bipyridine (bipy), 4,4′-dimethyl-2,2′-bipyridine (Me2bipy), or N,N,N′,N′-tetramethylethylenediamine (tmeda)] react with silanols HOSiR3 in toluene giving the corresponding siloxo complexes [Pd(N–N)(C6F5)(OSiR3)]. The X-ray crystal structure of [Pd(tmeda)(C6F5)(OSiPh3)] has been determined. In one of the two molecules in the asymmetric unit there is an intramolecular interaction by phenyl–pentafluorophenyl π-stacking.
Synthesis of New 8-Arylisoquinoline Derivatives by Application of Palladium-Catalyzed Suzuki Cross-Coupling Reactions.
2005
Abstract New 8-(het)aryltetrahydroisoquinolines ( 10–14 ), 8-aryltetrahydroisoquinolin-4-ols ( 15 , 16 ), and 8-phenylisoquinolin-4-ol ( 17 ), flexible analogues of aporphine, were synthesized in good yields using palladium-catalyzed Suzuki cross-coupling reactions from 8-bromotetrahydroisoquinolin-4-one ( 6 ) as a common intermediate. We also describe the synthesis of this novel intermediate through an easy and efficient method, which involved intramolecular Friedel–Crafts cyclization.