Rhodium-catalyzed coupling-cyclization reaction of isocyanides and 2-azidophenyloxyacrylates: synthesis of N-(3-substituted benzo[d]oxazol-2(3H)-ylidene)amines and dihydrobenzo[d]oxazoles

2022 ◽  
Author(s):  
Ming Yang ◽  
Xue-Cen Xu ◽  
Yue Gong ◽  
Yu-long Zhao
Keyword(s):  
Cyclization Reaction ◽  
First Time

A rhodium-catalyzed coupling cyclization of isocyanides with 2-azidophenyloxyacrylates has been developed for the first time. This reaction allows divergent syntheses of two significant N-heterocycles, five-membered N-(3-substituted benzo[d]oxazol-2(3H)-ylidene)amines and dihydrobenzo[d]oxazoles, from...

N-Selenocyanato-dibenzenesulfonimide: a new electrophilic selenocyanation reagent

Synthesis ◽  
2021 ◽  
Author(s):  
Deng Zhu ◽  
Ai-Hui Ye ◽  
Zhi-Min Chen
Keyword(s):  
Lewis Acid ◽  
Cyclization Reaction ◽  
First Time

A new electrophilic selenocyanation reagent N-selenocyanato-dibenzenesulfonimide was readily prepared in two steps from commercially available dibenzenesulfonimide for the first time. A variety of electrophilic selenocyanato reactions of nucleophiles have been achieved using it as selenocyanato source under mild and simple conditions. Numberous SeCN-containing compounds were obtained with moderate to excellent yields. Meanwhile, a Lewis-acid-mediated tandem selenocyanation/cyclization reaction of alkenes with phenols, which provided simple methods for the formation of various SeCN-containing chromanes and dihydrobenzofurans in moderate to good yields, has also been developed.

A novel one-pot multi-component synthesis of 3,3’-disubstituted oxindole and spirooxindole scaffolds via Sn-catalyzed C(sp3)–H functionalization of azaarenes by sequential Knoevenagel–Michael-cyclization reaction

RSC Advances ◽  
2015 ◽  
Vol 5 (99) ◽  
pp. 81103-81107 ◽  
Author(s):  
Santosh S. Chavan ◽  
Mohsinkhan Y. Pathan ◽  
Shridhar H. Thorat ◽  
Rajesh Gonnade ◽  
Shafeek A. R. Mulla
Keyword(s):  
Cyclization Reaction ◽  
One Pot ◽  
Bond Functionalization ◽  
Active Methylene Compounds ◽  
First Time ◽  
Active Methylene

Sn-catalyzed C(sp3)–H bond functionalization of 2-methyl azaarenes/2-(azaaryl)methanes has been achieved for the first time in a one-pot reaction with isatin and active methylene compounds.

Statistical Kinetics of Hevea Rubber Cyclization

1952 ◽  
Vol 25 (4) ◽  
pp. 784-800
Author(s):  
M. Gordon
Keyword(s):  
Cyclization Reaction ◽  
Acidity Function ◽  
Statistical Effect ◽  
Copolymer Structure ◽  
Reduced Rate ◽  
Cyclization Rate ◽  
First Time ◽  
Transition Complex ◽  
Kinetics Of ◽  
Better Than

Abstract Rubber cyclization provides a useful illustration of statistical effects intervening in the reactions of long-chain polymers. Analogously to the known cyclizations of simple diisoprenic terpenes, each individual cyclization act links two adjacent isoprene units in the rubber chain into a six-membered ring. However, some of the units remain stranded between neighboring rings and escape cyclization for want of a partner. Thus the final polymer has a copolymer structure of 86.5 per cent of diisoprenic rings and 13.5 per cent of uncyclized monisoprenic units. This result is derived from a statistical theory of Flory, and has previously found accurate experimental verification. The bearing of this statistical effect on the reaction kinetics has now been studied for the first time. Dilatometric experiments on rubber emulsions in sulfuric acid have shown that the cyclization reaction conforms in the main with a statistical cyclization law much better than with a first-order equation uncorrected for the survival of stranded units. High accuracy was required for this experimental distinction, whose importance lies in the implicit proof that the polymer units participate in the rate-determining transition complex, in accordance with the accepted proton transfer mechanism. A kinetic proof has incidentally been furnished for the fact that the rubber polymer contains long chains of identical units. When handled by an emulsion technique, this polymer can provide a useful “model compound” for its simpler terpene analogs. Certain rate abnormalities have been observed, including an induction period of reduced rate, probably connected with diffusion effects. A small volume change subsequent to the cyclization reaction may reflect a prototropic double-bond shift. The activation energy and entropy are found to be lower than in previous work, an effect traced in part to a curvature of the Arrhenius plot. The known dependence of cyclization rate on Hammett's acidity function H0 is quantitatively confirmed.

scholarly journals Novel Approach for the Synthesis of Chlorophosphazene Cycles with a Defined Size via Controlled Cyclization of Linear Oligodichlorophosphazenes [Cl(PCl2=N)n–PCl3]+[PCl]6–

2021 ◽  
Author(s):  
Mikhail Gorlov ◽  
Nikolay Bredov ◽  
Andrey Esin ◽  
Igor Sirotin ◽  
Mikhail Soldatov ◽  
...  
Keyword(s):  
Elevated Temperature ◽  
General Formula ◽  
Ammonium Chloride ◽  
Linear Chain ◽  
Cyclization Reaction ◽  
Direct Production ◽  
Novel Approach ◽  
Side Interaction ◽  
Cyclic Compounds ◽  
First Time

Despite a significant number of investigations in the field of phosphazene chemistry, the mechanism of this class cyclic compounds formation is still poorly studied. At the same time, a thorough understanding of this process is necessary both for the direct production of phosphazene rings with a given size, and for the controlled cyclization reaction when it is secondary and undesirable. Here we have synthesized a series of short linear phosphazene oligomers with the general formula Cl[PCl2=N]n–PCl3+PCl6– and studied their tendency to form cyclic structures under the influence of elevated temperature or in the presence of nitrogen-containing agents, such as hexamethyldisilazane (HMDS) or ammonium chloride. It was established that linear oligophosphazenes are inert when heated in the absence of the mentioned cyclization agents, and the formation of cyclic products occurs only when these agents are involved in the process. It is for the first time shown the ability to obtain the desired size phosphazene cycle from corresponding linear chain. Known obstacles like side interaction with the PCl6– counterion and a tendency of longer chains to undergo crosslinking elongation instead of cyclization are still relevant and ways to overcome them are being discussed.

Statistical Kinetics of Hevea Rubber Cyclization

1951 ◽  
Vol 24 (4) ◽  
pp. 924-939 ◽  
Author(s):  
M. Gordon
Keyword(s):  
Cyclization Reaction ◽  
Acidity Function ◽  
Statistical Effect ◽  
Copolymer Structure ◽  
Reduced Rate ◽  
Cyclization Rate ◽  
First Time ◽  
Transition Complex ◽  
Kinetics Of ◽  
Better Than

Abstract Rubber cyclization provides a useful illustration of statistical effects intervening in the reactions of long-chain polymers. Analogously to known cyclizations of simple diisoprenic terpenes, each individual cyclization act links two adjacent isoprene units in the rubber chain into a six-membered ring. However, some of the units remain stranded between neighboring rings and escape cyclization for want of a partner. Thus the final polymer has a copolymer structure of 86.5 per cent of diisoprenic rings and 13.5 per cent of uncyclized monisoprenic units. This result is derived from a statistical theory of Flory, and has previously found accurate experimental verification. The bearing of this statistical effect on the reaction kinetics has now been studied for the first time. Dilatometric experiments on rubber emulsions in sulfuric acid have shown that the cyclization reaction conforms in the main with a statistical cyclization law much better than with a first-order equation uncorrected for the survival of stranded units. High accuracy was required for this experimental distinction, whose importance lies in the implicit proof that the polymer units participate in the rate-determining transition complex, in accordance with the accepted proton transfer mechanism. A kinetic proof has incidentally been furnished for the fact that the rubber polymer contains long chains of identical units. When handled by an emulsion technique, this polymer can provide a useful “model compound” for its simpler terpene analogs. Certain rate abnormalities have been observed, including an induction period of reduced rate, probably connected with diffusion effects. A small volume change subsequent to the cyclization reaction may reflect a prototropic double-bond shift. The activation energy and entropy are found to be lower than in previous work, an effect traced in part to a curvature of the Arrhenius plot. The known dependence of cyclization rate on Hammett's acidity function H0 is quantitatively confirmed.

Direct synthesis of 4-hydroxycoumarins and 4-hydroxy-6-methyl-2-pyrone containing chroman-4-ones via silver catalyzed radical cascade cyclization reaction

2021 ◽  
Author(s):  
Suraj Sharma ◽  
Bipul Sarma ◽  
Gakul Baishya
Keyword(s):  
Direct Synthesis ◽  
Cyclization Reaction ◽  
Cascade Cyclization ◽  
Radical Cascade ◽  
First Time

For the first time, we report a novel silver catalyzed radical cascade cyclization reaction of 2-(allyloxy)arylaldehydes to synthesize two new libraries of chroman-4-ones by using 4-hydroxycoumarins and 4-hydroxy-6-methyl-2-pyrone as radical...

Statistical kinetics of Hevea rubber cyclization

1951 ◽  
Vol 204 (1079) ◽  
pp. 569-585 ◽  
Keyword(s):  
Cyclization Reaction ◽  
Acidity Function ◽  
Statistical Effect ◽  
Diffusion Effects ◽  
Reduced Rate ◽  
Cyclization Rate ◽  
First Time ◽  
Transition Complex ◽  
Kinetics Of ◽  
Better Than

Rubber cyclization provides a useful illustration of statistical effects intervening in the reactions of long-chain polymers. Analogously to the known cyclizations of simple diisoprenic terpenes, each individual cyclization act links two adjacent isoprene units in the rubber chain into a six-membered ring. However, some of the units remain stranded between neighbouring rings and escape cyclization for want of a partner. Thus the final polymer has a co-polymer structure of 86.5% of di-isoprenic rings and 13.5% of uncyclized monisoprenic units. This result is derived from a statistical theory of Flory, and has previously found accurate experimental verification. The bearing of this statistical effect on the reaction kinetics has now been studied for the first time. Dilatemetric experiments on rubber emulsions in sulphuric acid have shown that the cyclization reaction conforms in the main with a statistical cyclization law much better than with a first-order equation uncorrected for the survival of stranded units. High accuracy was required for this experimental distinction, whose importance lies in the implicit proof that the polymer units participate in the rate-determining transition complex, in accordance with the accepted proton transfer mechanism. A kinetic proof has incidentally been furnished for the fact that the rubber polymer contains long chains of identical units. When handled by an emulsion technique, this polymer can provide a useful ‘model compound’ for its simpler terpene analogues. Certain rate abnormalities have been observed including an induction period of reduced rate, probably connected with diffusion effects. A small volume change subsequent to the cyclization reaction may reflect a prototropic double-bond shift. The activation energy and entropy are found to be lower than in previous work, an effect traced in part to a curvature of the Arrhenius plot. The known dependence of cyclization rate on Hammett’s acidity function H 0 is quantitatively confirmed.

scholarly journals Transition-metal-free intramolecular Friedel–Crafts reaction by alkene activation: A method for the synthesis of some novel xanthene derivatives

2021 ◽  
Vol 17 ◽  
pp. 2203-2208
Author(s):  
Tülay Yıldız ◽  
İrem Baştaş ◽  
Hatice Başpınar Küçük
Keyword(s):  
Transition Metal ◽  
Trifluoroacetic Acid ◽  
Room Temperature ◽  
Synthesis Method ◽  
Biological Significance ◽  
Cyclization Reaction ◽  
Metal Free ◽  
New Synthesis ◽  
Xanthene Derivatives ◽  
First Time

In this work, new derivatives (substituted 9-methyl-9-arylxanthenes) of xanthene compounds (5a–l) of possible biological significance were synthesized by developing a new synthesis method. In order to obtain xanthene derivatives, the original alkene compounds to be used as the starting materials were synthesized in four steps using appropriate reactions. A cyclization reaction by intramolecular Friedel–Crafts alkylation was carried out in order to synthesize the desired xanthene derivatives using the alkenes as starting compounds. The intramolecular Friedel–Crafts reaction was catalyzed by trifluoroacetic acid (TFA) and provided some novel substituted 9-methyl-9-arylxanthenes with good yields at room temperature within 6–24 hours. As a result, an alkene compound was used for activation with TFA in the synthesis of xanthene through intramolecular Friedel–Crafts alkylation for the first time.

Annulate lamellae in the Sertoli cells of guinea pig testis after unilateral torsion of the spermatic cord

1984 ◽  
Vol 42 ◽  
pp. 196-197
Author(s):  
J. Chakraborty ◽  
A. P. Sinha Hikim ◽  
J. S. Jhunjhunwala
Keyword(s):  
Sertoli Cells ◽  
Guinea Pigs ◽  
Spermatic Cord ◽  
Present Report ◽  
Cell Types ◽  
Annulate Lamellae ◽  
Spermatogenic Cells ◽  
Electron Microscopic ◽  
Structural Details ◽  
First Time

Although the presence of annulate lamellae was noted in many cell types, including the rat spermatogenic cells, this structure was never reported in the Sertoli cells of any rodent species. The present report is based on a part of our project on the effect of torsion of the spermatic cord to the contralateral testis. This paper describes for the first time, the fine structural details of the annulate lamellae in the Sertoli cells of damaged testis from guinea pigs.One side of the spermatic cord of each of six Hartly strain adult guinea pigs was surgically twisted (540°) under pentobarbital anesthesia (1). Four months after induction of torsion, animals were sacrificed, testes were excised and processed for the light and electron microscopic investigations. In the damaged testis, the majority of seminiferous tubule contained a layer of Sertoli cells with occasional spermatogonia (Fig. 1). Nuclei of these Sertoli cells were highly pleomorphic and contained small chromatinic clumps adjacent to the inner aspect of the nuclear envelope (Fig. 2).

Electron spectroscopic imaging and diffraction

1991 ◽  
Vol 49 ◽  
pp. 706-707
Author(s):  
M. Rühle ◽  
J. Mayer ◽  
J.C.H. Spence ◽  
J. Bihr ◽  
W. Probst ◽  
...  
Keyword(s):  
Materials Science ◽  
Electron Spectroscopic Imaging ◽  
Magnetic Filter ◽  
Magnetic Imaging ◽  
Illumination System ◽  
Probe Size ◽  
Diffraction Patterns ◽  
Fritz Haber ◽  
Koehler Illumination ◽  
First Time

A new Zeiss TEM with an imaging Omega filter is a fully digitized, side-entry, 120 kV TEM/STEM instrument for materials science. The machine possesses an Omega magnetic imaging energy filter (see Fig. 1) placed between the third and fourth projector lens. Lanio designed the filter and a prototype was built at the Fritz-Haber-Institut in Berlin, Germany. The imaging magnetic filter allows energy-filtered images or diffraction patterns to be recorded without scanning using efficient area detection. The energy dispersion at the exit slit (Fig. 1) results in ∼ 1.5 μm/eV which allows imaging with energy windows of ≤ 10 eV. The smallest probe size of the microscope is 1.6 nm and the Koehler illumination system is used for the first time in a TEM. Serial recording of EELS spectra with a resolution < 1 eV is possible. The digital control allows X,Y,Z coordinates and tilt settings to be stored and later recalled.

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