Search results for "Metathesis"

Electrodialysis Applications in Wastewater Treatment for Environmental Protection and Resources Recovery: A Systematic Review on Progress and Perspec…

2020

This paper presents a comprehensive review of studies on electrodialysis (ED) applications in wastewater treatment, outlining the current status and the future prospect. ED is a membrane process of separation under the action of an electric field, where ions are selectively transported across ion-exchange membranes. ED of both conventional or unconventional fashion has been tested to treat several waste or spent aqueous solutions, including effluents from various industrial processes, municipal wastewater or salt water treatment plants, and animal farms. Properties such as selectivity, high separation efficiency, and chemical-free treatment make ED methods adequate for desalination and othe…

Unique Reactivity of Fluorinated Molecules with Transition Metals

2014

Organofluorine and organometallic chemistry by themselves constitute two potent areas in organic synthesis. Thus, the combination of both offers many chemical possibilities and represents a powerful tool for the design and development of new synthetic methodologies leading to diverse molecular structures in an efficient manner. Given the importance of the selective introduction of fluorine atoms into organic molecules and the effectiveness of transition metals in C–C and C–heteroatom bond formation, this review represents an interesting read for this aim.

1972

The metathesis reaction of cyclooctene was investigated with respect to the solvent, the catalyst, and the ratio of its components. A necessary condition for an active metathesis catalyst appears to be the presence of two transition metal-carbon bonds in a complex of the transition metal compound with an aluminum halide. A structure for the active complex is proposed. Die Metathese-Reaktion von Cycloocten wurde unter dem Einflus verschiedener Losungsmittel, verschiedener Katalysatorsysteme und Verhaltnisse der Katalysatorkomponenten untersucht. Die Ergebnisse lassen darauf schliesen, das die aktiven Katalysatoren Komplexe besonderer Ubergangsmetallverbindungen mit Aluminiumhalogeniden darst…

Stepwise synthesis and selective dimerisation of bis- and trisloop tetra-urea calix[4]arenes.

2008

Tetra-urea calix[4]arenes substituted with four mono- or bisalkenyl residues have been converted into bis- or tetraloop compounds by intramolecular olefin metathesis, with use of a tetratosylurea calix[4]arene as template. The same strategy has now been used to synthesise trisloop compounds and bisloop compounds with adjacent loops, completing the series of the loop-containing tetra-urea derivatives. A tetra-urea calix[4]arene of the AABB type, where A stands for a bisalkenyl- and B for a monoalkenyl-substituted urea unit, was used as precursor for the three loops. It was easily synthesised from a tetraamino calix[4]arene in which two adjacent amino groups were Boc-protected. The ABCB-type …

Topologically Novel Multiple Rotaxanes and Catenanes Based on Tetraurea Calix[4]arenes

2006

Calix[4]arenes bearing at their wide rim four urea residues easily form hydrogen bonded dimeric capsules. This has been used to preorganise alkenyl functions attached to these urea groups for their controlled connection via metathesis reaction. Multimacrocyclic tetraurea derivatives are thus obtained in excellent yields via heterodimers which are formed exclusively with tetratosylurea derivatives. Heterodimerisation of such bis- and tetraloop tetraureas leads analogously to multicatenanes, or to rotaxanes by stoppering. Huge macrocycles are detached from tetraloop derivatives by cleavage of the urea function.

Template synthesis of multi-macrocycles by metathesis reaction.

2004

Selective heterodimerisation of tetraurea calix[4]arenes containing four or eight ω-alkenyl groups with a tetratosyl urea calix[4]arene has been effectively used to synthesize multi-macrocycles via metathesis reaction.

Diastereoselective Intramolecular Additions of Allyl- and Propargylsilanes to Iminium Ions: Synthesis of Cyclic and Bicyclic Quaternary Amino Acids

2010

Chiral imino lactones derived from (R)-phenylglycinol containing an allyl- or propargyltrimethylsilyl group in the side chain readily cyclized in the presence of acidic reagents to afford spirocyclic compounds with high diastereoselectivity. Removal of the chiral auxiliary produced 2-substituted 1-aminocycloalkanecarboxylic acids, whereas further cyclizations by means of metathesis or hydroamination reactions led to bicyclic derivatives of pipecolic acid and proline.

N-sulfinyl amines as a nitrogen source in the asymmetric intramolecular aza-Michael reaction: total synthesis of (-)-pinidinol.

2010

N-Sulfinyl amines have been successfully employed as nitrogen nucleophiles for the asymmetric intramolecular aza-Michael reaction. The synthetic strategy involves a cross-metathesis reaction followed by the Michael-type cyclization, either in a base-catalyzed two-step procedure or in a tandem fashion. The developed methodology allows access to chiral substituted pyrrolidines and piperidines bearing one or two stereocenters and it has been applied to the synthesis of the piperidine alkaloid (-)-pinidinol.

Stereoselective synthesis and determination of the cytotoxic properties of spicigerolide and three of its stereoisomers.

2003

Stereoselective syntheses of the naturally occurring, cytotoxic lactone spicigerolide and three nonnatural stereoisomers thereof are described. The commercially available sugar l-rhamnose was in all cases the chiral starting material. Key steps in each of these syntheses were asymmetric Brown allylations and ring-closing metatheses. The cytotoxic activities of the four lactones against a range of tumoral lines were then determined.

(2,2‐Dibromovinyl)ferrocene as a Building Block for the Assembly of Heterodinuclear Complexes – Preparation of an σ‐Alkenylpalladium Complex and Dime…

2007

The oxidative addition of (2,2-dibromovinyl)ferrocene [Br2C=C(H)–Fc] (1) to [Pd(PPh3)4] yields the heterodinuclear σ-alkenyl complex trans-[{Pd(Br)(PPh3)2}–C(Br)=C(H)–Fc] (2). Nucleophilic attack of sodium thiolates on 1 unexpectedly affords the vinyl thioether derivatives (Z)-[(RS)(H)C=C(H)–Fc] (4a: R = Ph; 4b: R = tBu; 4c: R = Et). Complexes 4a and 4c can also be prepared by addition of NaSR across the triple bond of Fc–C≡C–H (3). Addition of an excess of NaSR to 1 affords the dithioether derivatives (Z)-[(RS)(H)C=C(SR)–Fc] (5a: R = Ph; 5b: R = p-tolyl; 5c: R = Et). An addition/elimination sequence is suggested to account for this surprising result. The yield of 5c is very low due to a co…