Search results for "Regioselectivity"
showing 10 items of 298 documents
Selective Derivatization of Resorcarenes. 3. C2-Symmetrical and Transcavity Bridged Bis-Benzoxazines Derived from C2v-Symmetrical Tetratosylates
1998
The regioselective condensation of resorcarene tetratosylates 3/4 with formaldehyde and various primary amines readily gives bis-benzoxazines 5/6 in 65−86% yield. The chiral, C2-symmetrical structure of these compounds has been proved by NMR-spectroscopy and single-crystal X-ray analysis. Bis-benzoxazines 5f and 5i assume in the crystalline state a boat conformation in which the two resorcinol rings bearing the oxazine fragments are nearly parallel. The tosylated resorcinol units are horizontally arranged in a propeller-like fashion, and two intramolecular hydrogen bonds are formed between the phenolic hydroxy groups and the oxygens of the neighboring sulfonyl fragments. Molecular mechanics…
Methyl [4-methoxy-3-(methylsulfonyloxy)benzoyl]formate
2005
The crystal structure of the title compound, C11H12O7S, confirms an earlier proposal concerning the regioselectivity of electrophilic substitution reactions of mesyl guaiacol.
Syntheses of dopaminergic 1-cyclohexylmethyl-7,8-dioxygenated tetrahydroisoquinolines by selective heterogeneous tandem hydrogenation
2002
Abstract We describe the preparation in a ‘one-pot’ sequence 1-cyclohexylmethyl 7,8-dioxygenated tetrahydroisoquinoline, substituted and unsubstituted in the C ring by application of the Photo–Fries transposition, followed by a tandem reduction–cyclization and further reduction. Indeed, we have accomplished for the first time regioselective hydrogenation of the benzylic ring of the tetrahydroisoquinoline systems. All 1-cyclohexylmethyl THIQ synthesized were able to displace D2 dopamine receptor from its specific binding site in rat striatal membranes, while the N-methylated derivatives showed also affinity for D1 dopamine receptors.
Synthesis of new fluorinated Tebufenpyrad analogs with acaricidal activity through regioselective pyrazole formation.
2008
In previous studies, our group has shown that the use of fluorinated alcohols such as trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP) as solvents dramatically increases the regioselectivity in the pyrazole formation from 1,3-diketone with methylhydrazine. We have now applied this synthetic method to the preparation of new fluorinated pyrazoles, which have then been used as synthetic intermediates in the preparation of fluorinated analogs of Tebufenpyrad, a commercial acaricide. These compounds display a strong acaricidal activity that is either comparable to or better than that of the commercial compound.
A Regio- and Diastereoselective Anodic Aryl-Aryl Coupling in the Biomimetic Total Synthesis of (-)-Thebaine.
2018
The biosynthesis of thebaine is based on the regioselective, intramolecular, oxidative coupling of (R)-reticuline. For decades, chemists have sought to mimic this coupling by using stoichiometric oxidants. However, all approaches to date have suffered from low yields or the formation of undesired regioisomers. Electrochemistry would represent a sustainable alternative in this respect but all attempts to accomplish an electrochemical synthesis of thebaine have failed so far. Herein, a regio- and diastereoselective anodic coupling of 3',4',5'-trioxygenated laudanosine derivatives is presented, which finally enables electrochemical access to (-)-thebaine.
Synthesis and Photoelectrical Properties of 3-(Diphenylamino)Carbazolyl-Functionalized DMABI Derivatives
2019
A modular approach was used in the synthesis of the 3-(diphenylamino)carbazolyl- functionalized 2-(4-(dimethylamino)benzylidene)-1H-indene-1,3(2H)-dione (DMABI) derivatives. For this purpose, carboxyl functional group was introduced into the framework of DMABI molecule. Additionally, a regioselective method for substitution of carbonyl group of DMABI with dicyanomethylene group was investigated and verified using the heteronuclear multiple bond correlation NMR spectra. Steglich esterification method was used to connect the 3‑(diphenylamino)carbazolyl moiety via an unconjugated spacer. The UV-Vis absorption spectra and molecular energy level data were obtained for the evaluation of the synth…
Molecular orbital studies on brominated diphenyl ethers. Part II—reactivity and quantitative structure–activity (property) relationships
2005
Polybrominated diphenyl ethers (PBDEs) are widely used as flame retardants and are increasingly turning up in the environment. Their structural similarities to polychlorinated biphenyls and thyroid hormones suggest they may be a risk to human health. The present study examines the reactivity of brominated diphenyl ethers (BDEs) on the basis of the electronic structures as calculated by semiempirical AM1 self-consistent field molecular orbital (SCF-MO) method. Frontier orbital energies were used to elucidate the reactivity of BDEs in electrophilic, nucleophilic and photolytic reactions. From an examination of the frontier electron densities, the regioselectivity, or orientation, of metabolic…
Metal-Free and User-Friendly Regioselective Hydroxyfluorination of Olefins
2018
A simple, user-friendly, metal-free protocol for the regioselective anti-Markovnikov hydrofluorination of olefins using readily available and inexpensive reagents has been developed. This new approach displays a broader scope than previously reported methodologies and has been applied to the late-stage fluorination of a complex molecule, giving rise to a fluorosteroid derivative. The stereochemistry of the process has also been studied in some detail.
Synthesis of vinca alkaloids and related compounds LX. A simple transformation of apovincamine into vincamine
1992
Abstract The 15α-chloro-vincamine derivative 2 was prepared and proved to be key intermediate of a two-step transformation of apovincamine into vincamine. The structure of 2 was established via detailed NMR and X-ray investigations.
Solvent-Enhanced Diastereo- and Regioselectivity in the PdII-Catalyzed Synthesis of Six- and Eight-Membered Heterocycles viacis-Aminopalladation
2009
The Pd(II)-catalyzed intramolecular oxidative cyclization of tosyl-protected cis- and trans-N-allyl-2-aminocyclohexanecarboxamides was examined, and efficient syntheses of cyclohexane-fused pyrimidin-4-ones and 1,5-diazocin-6-ones were developed. In the course of the research, a marked solvent effect was observed on both the regio- and diastereoselectivity. Additionally, a novel Pd(II)-mediated domino oxidation, oxidative amination reaction was discovered. Our experimental and theoretical findings suggest that the reactions proceed via a cis-aminopalladation mechanism.