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Stannatrane
A stannatrane (IUPAC: 1-aza-5-stannabicyclo .3.3ndecane) is a tin-based atrane belonging to the larger class of organostannanes. Though the term stannatrane is often used to refer to the more commonly employed carbastannatrane, azastannatranes have also been synthesized (prefix refers to the identity of the atom bound directly to tin center). Stannatrane reagents offer highly selective methods for the incorporation of "R" substituents in complex molecules for late-stage diversification. These reagents differ from their tetraalkyl organostannane analogues in that there is no participation of dummy ligands in the transmetalation step, offering selective alkyl transfer in Stille Coupling reactions. These transmetalating agents are known to be air- and moisture-stable, as well as generally less toxic than their tetraalkyl counterparts. History and structural properties The first carbastannatrane was reported in 1984 by Jurkschat and Tzschach. By reaction of an amino-tri Grignar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stannatrane Lithiation
A stannatrane (IUPAC: 1-aza-5-stannabicyclo[3.3.3]undecane) is a tin-based atrane belonging to the larger class of Organotin chemistry, organostannanes. Though the term stannatrane is often used to refer to the more commonly employed carbastannatrane, azastannatranes have also been synthesized (prefix refers to the identity of the atom bound directly to tin center). Stannatrane reagents offer highly selective methods for the incorporation of "R" substituents in complex molecules for late-stage diversification. These reagents differ from their tetraalkyl organostannane analogues in that there is no participation of dummy ligands in the transmetalation step, offering selective alkyl transfer in Stille coupling, Stille Coupling reactions. These transmetalating agents are known to be air- and moisture-stable, as well as generally less toxic than their tetraalkyl counterparts. History and structural properties The first carbastannatrane was reported in 1984 by Jurkschat and Tzschach. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atrane
Atranes are a class of tricyclic molecules with three five-membered rings. It is a heterocyclic structure similar to the propellanes. It has a transannular dative bond from a nitrogen at one bridgehead to a Lewis acidic atom such as silicon or boron at the other bridgehead.Voronkov, Mikhail G.; Baryshok, Viktor P. "Atranes - a new generation of biologically active substances" (in Russian) Vestnik Rossiiskoi Akademii Nauk 2010, volume 80, 985-992. The name "atrane" was first proposed by . Nomenclature Various atranes are named depending on the central element, e.g. "silatrane" (E = silicon); "boratrane" (E = boron); "phosphatrane" (E = phosphorus), etc. It is also proposed that when Y = nitrogen, the prefix "aza" be inserted before ''element'' + "atrane" (azasilatrane, for example) because atranes wherein E = silicon and Y = oxygen have been referred to as just "silatranes". Structure and properties Silatranes exhibit unusual properties as well as biological activity in w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stille Coupling
The Stille reaction is a chemical reaction widely used in organic synthesis. The reaction involves the coupling of two organic groups, one of which is carried as an organotin compound (also known as organostannanes). A variety of organic electrophiles provide the other coupling partner. The Stille reaction is one of many palladium-catalyzed coupling reactions.Hartwig, J. F. ''Organotransition Metal Chemistry, from Bonding to Catalysis''; University Science Books: New York, 2010. Stille, J. K. '' Angew. Chem. Int. Ed. Engl.'' 1986, ''25'', 508–524.ReviewFarina, V.; Krishnamurthy, V.; Scott, W. J. ''Org. React.'' 1998, ''50'', 1–652.Review : + \ \ce \ \overbrace^ + \!-\! :*\!,\ : Allyl, alkenyl, aryl, benzyl,acyl :*: halides (Cl, Br, I), pseudohalides (, OPO(OR)2), OAc The R1 group attached to the trialkyltin is normally sp2-hybridized, including vinyl, and aryl groups. These organostannanes are also stable to both air and moisture, and many of these reagents either are com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organotin Chemistry
Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin chemistry is part of the wider field of organometallic chemistry. The first organotin compound was diethyltin diiodide (), discovered by Edward Frankland in 1849. The area grew rapidly in the 1900s, especially after the discovery of the Grignard reagents, which are useful for producing Sn–C bonds. The area remains rich with many applications in industry and continuing activity in the research laboratory. Structure Organotin compounds are generally classified according to their oxidation states. Tin(IV) compounds are much more common and more useful. Organic derivatives of tin(IV) The tetraorgano derivatives are invariably tetrahedral. Compounds of the type SnRR'R''R have been resolved into individual enantiomers. Organotin halides Organotin chlorides have the formula for values of ''n'' up to 3. Bromides, iodides, and fluorides are also known but less important. These ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Palladium
Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired by her when she slew Pallas. Palladium, platinum, rhodium, ruthenium, iridium and osmium form a group of elements referred to as the platinum group metals (PGMs). They have similar chemical properties, but palladium has the lowest melting point and is the least dense of them. More than half the supply of palladium and its congener platinum is used in catalytic converters, which convert as much as 90% of the harmful gases in automobile exhaust (hydrocarbons, carbon monoxide, and nitrogen dioxide) into nontoxic substances (nitrogen, carbon dioxide and water vapor). Palladium is also used in electronics, dentistry, medicine, hydrogen purification, chemical applications, groundwate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrophile
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carries a partial positive charge, or have an atom that does not have an octet of electrons. Electrophiles mainly interact with nucleophiles through addition and substitution reactions. Frequently seen electrophiles in organic syntheses include cations such as H+ and NO+, polarized neutral molecules such as HCl, alkyl halides, acyl halides, and carbonyl compounds, polarizable neutral molecules such as Cl2 and Br2, oxidizing agents such as organic peracids, chemical species that do not satisfy the octet rule such as carbenes and radicals, and some Lewis acids such as BH3 and DIBAL. Organic chemistry Addition of halogens These occur between alkenes and electrophiles, often halogens as in halogen addition reactions. Common reactions i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lone Pair
In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC ''Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lone pairs are found in the outermost electron shell of atoms. They can be identified by using a Lewis structure. Electron pairs are therefore considered lone pairs if two electrons are paired but are not used in chemical bonding. Thus, the number of electrons in lone pairs plus the number of electrons in bonds equals the number of valence electrons around an atom. Lone pair is a concept used in valence shell electron pair repulsion theory (VSEPR theory) which explains the shapes of molecules. They are also referred to in the chemistry of Lewis acids and bases. However, not all non-bonding pairs of electrons are considered by chemists to be lone pairs. Examples are the transition metals where the non-bonding pairs do not influence molecular ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetramethyltin
Tetramethyltin is an organometallic compound with the formula (CH3)4Sn. This liquid, one of the simplest organotin compounds, is useful for transition-metal mediated conversion of acid chlorides to methyl ketones and aryl halides to aryl methyl ketones. It is volatile and toxic, so care should be taken when using it in the laboratory. Synthesis and structure Tetramethyltin is synthesized by reaction of the Grignard reagent methylmagnesium iodide, with tin tetrachloride, which is synthesized by reacting tin metal with chlorine gas. :4 CH3MgI + SnCl4 → (CH3)4Sn + 4 MgICl In tetramethyltin, the metal surrounded by four methyl groups in a tetrahedral structure is a heavy analogue of neopentane. Applications Precursor to methyltin compounds Tetramethyltin is a precursor to trimethyltin chloride (and related methyltin halides), which are precursors to other organotin compounds. These methyltin chlorides are prepared via the so-called Kocheshkov redistribution reaction. Thus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trigonal Bipyramidal
In chemistry, a trigonal bipyramid formation is a molecular geometry with one atom at the center and 5 more atoms at the corners of a triangular bipyramid. This is one geometry for which the bond angles surrounding the central atom are not identical (see also pentagonal bipyramid), because there is no geometrical arrangement with five terminal atoms in equivalent positions. Examples of this molecular geometry are phosphorus pentafluoride (), and phosphorus pentachloride () in the gas phase. Axial (or apical) and equatorial positions The five atoms bonded to the central atom are not all equivalent, and two different types of position are defined. For phosphorus pentachloride as an example, the phosphorus atom shares a plane with three chlorine atoms at 120° angles to each other in ''equatorial'' positions, and two more chlorine atoms above and below the plane (''axial'' or ''apical'' positions). According to the VSEPR theory of molecular geometry, an axial position is more crowd ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Enantiomeric Excess
In stereochemistry, enantiomeric excess (ee) is a measurement of purity used for chiral substances. It reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0%, while a single completely pure enantiomer has an ee of 100%. A sample with 70% of one enantiomer and 30% of the other has an ee of 40% (70% − 30%). Definition Enantiomeric excess is defined as the absolute difference between the mole fraction of each enantiomer: :\ ee = , F_R - F_S, where :\ F_R + F_S = 1 In practice, it is most often expressed as a percent enantiomeric excess. The enantiomeric excess can be determined in another way if we know the amount of each enantiomer produced. If one knows the moles of each enantiomer produced then: Enantiomeric excess is used as one of the indicators of the success of an asymmetric synthesis. For mixtures of diastereomers, there are analogous definitions and uses for diastereomeric excess an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
One-pot Method
In chemistry a one-pot synthesis is a strategy to improve the efficiency of a chemical reaction whereby a reactant is subjected to successive chemical reactions in just one reactor. This is much desired by chemists because avoiding a lengthy separation process and purification of the intermediate chemical compounds can save time and resources while increasing chemical yield. An example of a one-pot synthesis is the total synthesis of tropinone or the Gassman indole synthesis. Sequential one-pot syntheses can be used to generate even complex targets with multiple stereocentres, such as oseltamivir, which may significantly shorten the number of steps required overall and have important commercial implications. A sequential one-pot synthesis with reagents added to a reactor one at a time and without work-up is also called a telescoping synthesis. In one such procedure the reaction of 3-N-tosylaminophenol I with acrolein II affords a hydroxyl substituted quinoline III through 4 seq ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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