Search results for "SELECTIVITY"
showing 10 items of 1148 documents
Regioselective Metal- and Reagent-Free Arylation of Benzothiophenes by Dehydrogenative Electrosynthesis.
2018
A novel strategy for the synthesis of biaryls consisting of a benzothiophene and a phenol moiety is reported. These heterobiaryls are of utmost interest for pharmaceutical, biological, and high-performance optoelectronic applications. The metal- and reagent-free, electrosynthetic, and highly efficient method enables the generation of 2- and 3-(hydroxyphenyl)benzo[b]thiophenes in a regioselective fashion. The described one-step synthesis is easy to conduct, scalable, and inherently safe. The products are afforded in high yields of up to 88 % and with exquisite selectivity. The reaction also features a broad scope and tolerates a large variety of functional groups.
Copper(I)-catalysed regioselective synthesis of pyrazolo[5,1-c]-1,2,4-triazoles: A DFT mechanistic study
2017
Abstract Formation of pyrazolo[5,1-c]-1,2,4-triazoles by means of Cu(I)-catalysed [3+2] cycloaddition (32CA) reactions of C,N-cyclic azomethine imines with phenylacetylene, experimentally reported by Katritzky et al. (JOC 2012, 77, 5813), was studied using the density functional theory (DFT) method. Comparison with the uncatalysed 32CA reaction indicates that the Cu(I) catalyst provides new reaction pathways with lower electronic energy barriers in dichloromethane as solvent. The mechanism proposed by Katritzky for the Cu(I) catalysed reaction is compared with that proposed by Sharpless et al. (JACS 127, 2005, 210). The major difference between these two mechanisms lies in the coordination …
Regio- and Stereoselective Synthesis of 3-Pyrazolylidene-2-oxindole Compounds by Nucleophilic Vinylic Substitution of (E)-3-(Nitromethylene)indolin-2…
2019
[EN] A highly regio- and stereoselective synthesis of 3-alkylidene-2-oxindoles has been described through a nucleophilic vinylic substitution (SNV) of (E)-3-(nitromethylene)indolin-2-one using pyrazol-3-ones as nucleophiles and Et3N as a base. The reaction affords selectively the Z-isomer when pyrazol-3-ones without substituents at the 4 position are used. While the reaction is E-selective with 4- substituted pyrazolones. The stereoselectivity (up to >20:1) and the yields (up to 98%) are very high under mild reaction conditions.
Total Synthesis of Stemoamide, 9a-epi-Stemoamide, and 9a,10-epi-Stemoamide: Divergent Stereochemistry of the Final Methylation Steps
2020
Total syntheses of stemoamide, 9a-epi-stemoamide, and 9a,10-epi-stemoamide by a convergent A + B ring-forming strategy is reported. The synthesis required a diastereoselective late-stage methylation of the ABC stemoamide core that successfully enabled access to three of the four possible diastereomeric structures. For the natural stemoamide series, the diastereoselectivity can be rationalized both by kinetic and thermodynamic arguments, whereas for the natural 9a-epi-stemoamide series, the kinetic selectivity is explained by the prepyramidalization of the relevant enolate.
Mechanism and cis/trans Selectivity of Vinylogous Nazarov-type [6π] Photocyclizations
2017
Vinylogous Nazarov-type cyclizations yield seven-membered rings from butadienyl vinyl ketones via a photochemical [6π] photocyclization followed by subsequent isomerization steps. The mechanism of this recently developed method was investigated using unrestricted DFT, SF-TDDFT, and CASSCF/NEVPT2 calculations, suggesting three different pathways that lead either to pure trans, pure cis, or mixed cis/trans configured products. Singlet biradicals or zwitterions occur as intermediates. The computational results are supported by deuterium-labeling experiments.
Systematic Investigation of Resorcin[4]arene-Based Cavitands as Affinity Materials on Quartz Crystal Microbalances.
2017
Resorcin[4]arene cavitands are well-known supramolecular hosts, and their outstanding guest-binding abilities in solution have been studied in detail in recent decades. In a systematic approach, different resorcin[4]arene cavitands and container molecules are characterized as affinity materials for gravimetric sensing using high-fundamental-frequency quartz crystal microbalances. Analysis of their affinity toward a series of various analytes reveals a remarkable dependence of both selectivity and sensitivity on the shape, accessibility, and size of the cavity, along with their supramolecular interactions with the host molecules.
Arene C−H Activation at Aluminium(I): meta Selectivity Driven by the Electronics of S N Ar Chemistry
2020
The reactivity of the electron-rich anionic Al(I) ('aluminyl') compound K 2 [(NON)Al] 2 (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di- tert -butyl-9,9-dimethylxanthene) towards mono- and disubstituted arenes is reported. C-H activation chemistry with n -butylbenzene gives exclusively the product of activation at the arene meta position. Mechanistically, this transformation proceeds in a single step via a concerted Meisenheimer-type transition state. Selectivity is therefore based on similar electronic factors to classical S N Ar chemistry, which implies the destabilization of transition states featuring electron-donating groups in either the ortho or the para positions. In the cases of tolu…
Squaramide-Catalyzed Asymmetric aza-Friedel-Crafts/N,O-Acetalization Domino Reactions Between 2-Naphthols and Pyrazolinone Ketimines
2017
N-Boc ketimines derived from pyrazolin-5-ones were explored to develop an unprecedented domino aza-Friedel-Crafts/N,O-acetalization reaction with 2-naphthols. The novel method requires a catalyst loading of only 0.5 mol % of a bifunctional squaramide catalyst, is scalable to gram amounts, and provides a new series of furanonaphthopyrazolidinone derivatives bearing two vicinal tetra-substituted stereogenic centers in excellent yields (95-98 %) and stereoselectivity (>99:1 d.r. and 97-98 % ee). A different reactivity was observed in the case of 1-naphthols and other electron-rich phenols, which led to the aza-Friedel-Crafts adducts in 70-98 % yield and 47-98 % ee.
Effect of Superbasic Ionic Liquids on the Synthesis of Dendritic PolyaminesviaAza-Michael Addition Reaction
2017
Catalytic effect of selected superbasic ionic liquids on the yield and selectivity of aza-Michael addition of ethylenediamine and ammonia to acrylonitrile was investigated. The reactions were performed in calorimetric reactor equipped with RT-IR probe (real-time IR), where all energy changes associated with chemical reactions and physical transformations were monitored. Catalytic activity of selected superbasic ionic liquids in aza-Michael addition ethylenediamine and ammonia to acrylonitrile were determined and obtained polynitriles were then hydrogenatated to final three- and four-directional dendritic polyamines. The products were characterized by instrumental analytical methods, includi…
Sensing and discrimination of cyanide and hydrogen sulfide using an 8-alkenyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene derivative
2016
8-(2-Phenylethenyl)BODIPY has been shown to be an appropriate chromo-fluorogenic probe for cyanide in H2O. Good selectivity and LOD values below the allowed cyanide concentration in drinking water were attained. Cyanide can be discriminated from hydrogen sulphide by an oxidation process with hydrogen peroxide.