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Barton–Zard Reaction
The Barton–Zard reaction is a route to pyrrole derivatives via the reaction of a nitroalkene with an α-isocyanide under basic conditions. pp.43-4 It is named after Derek Barton and Samir Zard who first reported it in 1985. Mechanism The mechanism consists of five steps: * Base catalyzed carbonyl enolization of the α-isocyanide. * Michael-type addition between the α-isocyanide carbonyl enolate and the nitroalkene. * 5-endo-dig cyclization (see: Baldwin's rules). * Base catalyzed elimination of the nitro group. * Tautomerization leading to aromatisation. Scope The nitro compound may be aromatic rather than just an alkene. The reaction has been used for the synthesis of polypyrroles, including porphyrins, as well as dipyrromethenes such as BODIPY BODIPY is the technical common name of a chemical compound with formula , whose molecule consists of a boron difluoride group joined to a dipyrromethene group ; specifically, the compound 4,4-difluoro-4-bora-3a,4a-diaza-'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyrrole
Pyrrole is a heterocyclic, aromatic, organic compound, a five-membered ring with the formula . It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., ''N''-methylpyrrole, . Porphobilinogen, a trisubstituted pyrrole, is the biosynthetic precursor to many natural products such as heme. Pyrroles are components of more complex macrocycles, including the porphyrinogens and products derived therefrom, including porphyrins of heme, the chlorins, bacteriochlorins, and chlorophylls. Properties, structure, bonding Pyrrole is a colorless volatile liquid that darkens readily upon exposure to air, and is usually purified by distillation immediately before use. Pyrrole has a nutty odor. Pyrrole is a 5-membered aromatic heterocycle, like furan and thiophene. Unlike furan and thiophene, it has a dipole in which the positive end lies on the side of the heteroatom, with a dipole moment of 1.58 D. In CDCl3, it ha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Derek Barton
Sir Derek Harold Richard Barton (8 September 1918 – 16 March 1998) was an English organic chemist and Nobel Prize laureate for 1969. Education and early life Barton was born in Gravesend, Kent, to William Thomas and Maude Henrietta Barton (''née'' Lukes). He attended Gravesend Grammar School (1926–29), The King's School, Rochester (1929–32), Tonbridge School (1932–35) and Medway Technical College (1937–39). In 1938 he entered Imperial College London, where he graduated in 1940 and obtained his PhD degree in Organic Chemistry in 1942. Career and research From 1942 to 1944, Barton was a government research chemist, then from 1944 to 1945 he worked for Albright and Wilson in Birmingham. He then became Assistant Lecturer in the Department of Chemistry of Imperial College, and from 1946 to 1949 he was ICI Research Fellow. During 1949 and 1950, he was a visiting lecturer in natural products chemistry at Harvard University, and was then appointed reader in organic c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Samir Zard
Samir Zard (born 1955) is a Lebanese-French chemist and the president of the department of chemistry at the École polytechnique, Paris, where he also directs the department of organic chemistry and synthesis. Biography Samir Zard was born in Ife, Nigeria ; he grew up in the suburbs of Lebanon. Zard initially studied chemistry at the American University of Beirut, but in 1975 he was forced to emigrate due to the Lebanese civil war. He completed his undergraduate education at Imperial College London, receiving the highest mark among his graduating class, and followed Sir Derek Barton to Université Paris-Sud for doctoral study. He defended his thesis in 1983 and subsequently started his research career at the Institut de Chimie des Substances Naturelles at Gif-sur-Yvette, at the time also directed by Barton. In 1986, he rejoined the organic chemistry department of the École polytechnique, where he has since worked. Work Zard and his group have made significant advances in t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Keto–enol Tautomerism
In organic chemistry, enols are a type of functional group or chemical intermediate, intermediate in organic chemistry containing a group with the formula (R = many substituents). The term ''enol'' is an abbreviation of ''alkenol'', a portmanteau deriving from "-ene"/"alkene" and the "-ol". Many kinds of enols are known. Keto–enol tautomerism refers to a chemical equilibrium between a "keto" form (a carbonyl, named for the common ketone case) and an enol. The interconversion of the two forms involves the transfer of an alpha hydrogen atom and the reorganisation of bonding electrons. The keto and enol forms are tautomerism, tautomers of each other. Enolization organic compound, Organic esters, ketones, and aldehydes with an α-hydrogen ( bond adjacent to the carbonyl group) often form enols. The reaction involves migration of a proton () from carbon to oxygen: : In the case of ketones, the conversion is called a keto-enol tautomerism, although this name is often more generall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isocyanide
An isocyanide (also called isonitrile or carbylamine) is an organic compound with the functional group –. It is the isomer of the related nitrile (–C≡N), hence the prefix is ''isocyano''.IUPAC Goldboo''isocyanides''/ref> The organic fragment is connected to the isocyanide group through the nitrogen atom, not via the carbon. They are used as building blocks for the synthesis of other compounds. Properties Structure and bonding The C-N distance in isocyanides is 115.8 pm in methyl isocyanide. The C-N-C angles are near 180°. Akin to carbon monoxide, isocyanides are described by two Resonance (chemistry), resonance structures, one with a triple bond between the nitrogen and the carbon and one with a double bond between. The π lone pair of the nitrogen stabilizes the structure and is responsible of the linearity of isocyanides, although the reactivity of isocyanides reflects some carbene character, at least in a formal sense. Thus, both resonance structures are useful repres ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Michael Reaction
In organic chemistry, the Michael reaction or Michael 1,4 addition is a reaction between a Michael donor (an enolate or other nucleophile) and a Michael acceptor (usually an α,β-unsaturated carbonyl) to produce a Michael adduct by creating a carbon-carbon bond at the acceptor's β-carbon. It belongs to the larger class of conjugate additions and is widely used for the mild formation of carbon–carbon bonds. The Michael addition is an important atom-economical method for diastereoselective and enantioselective C–C bond formation, and many asymmetric variants exist : In this general Michael addition scheme, either or both of R and R' on the nucleophile (the Michael donor) represent electron-withdrawing substituents such as acyl, cyano, nitro, or sulfone groups, which make the adjacent methylene hydrogen acidic enough to form a carbanion when reacted with the base, ''B:''. For the alkene (the Michael acceptor), the R" substituent is usually a carbonyl, which makes the co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cyclization
A cyclic compound (or ring compound) is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where all the atoms are carbon (i.e., are carbocycles), none of the atoms are carbon (inorganic cyclic compounds), or where both carbon and non-carbon atoms are present (heterocyclic compounds with rings containing both carbon and non-carbon). Depending on the ring size, the bond order of the individual links between ring atoms, and their arrangements within the rings, carbocyclic and heterocyclic compounds may be aromatic or non-aromatic; in the latter case, they may vary from being fully saturated to having varying numbers of multiple bonds between the ring atoms. Because of the tremendous diversity allowed, in combination, by the valences of common atoms and their ability to form rings, the number of possible cyclic structures, even of smal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Baldwin's Rules
Baldwin's rules in organic chemistry are a series of guidelines outlining the relative favorabilities of ring closure reactions in alicyclic compounds. They were first proposed by Jack Baldwin (chemist), Jack Baldwin in 1976. Baldwin's rules discuss the relative rates of ring closures of these various types. These terms are not meant to describe the absolute probability that a reaction will or will not take place, rather they are used in a relative sense. A reaction that is disfavoured (slow) does not have a rate that is able to compete effectively with an alternative reaction that is favoured (fast). However, the disfavoured product may be observed, if no alternate reactions are more favoured. The rules classify ring closures in three ways: *the number of atoms in the newly formed ring *into ''exo'' and ''endo'' ring closures, depending whether the bond broken during the ring closure is inside (''endo'') or outside (''exo'') the ring that is being formed *into ''tet'', ''trig'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aromatic Compound
Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were understood. The current definition of aromatic compounds does not have any relation to their odor. Aromatic compounds are now defined as cyclic compounds satisfying Hückel's rule. Aromatic compounds have the following general properties: * Typically unreactive * Often non polar and hydrophobic * High carbon-hydrogen ratio * Burn with a strong sooty yellow flame, due to high C:H ratio * Undergo electrophilic substitution reactions and nucleophilic aromatic substitutions Arenes are typically split into two categories - benzoids, that contain a benzene derivative and follow the benzene ring model, and non-benzoids that contain other aromatic cyclic derivatives. Aromatic compounds are commonly used in organic synthesis and are involved in m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Porphyrins
Porphyrins ( ) are heterocyclic, macrocyclic, organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (). In vertebrates, an essential member of the porphyrin group is heme, which is a component of hemoproteins, whose functions include carrying oxygen in the bloodstream. In plants, an essential porphyrin derivative is chlorophyll, which is involved in light harvesting and electron transfer in photosynthesis. The parent of porphyrins is porphine, a rare chemical compound of exclusively theoretical interest. Substituted porphines are called porphyrins. With a total of 26 π-electrons the porphyrin ring structure is a coordinated aromatic system. One result of the large conjugated system is that porphyrins absorb strongly in the visible region of the electromagnetic spectrum, i.e. they are deeply colored. The name "porphyrin" derives . Structure Porphyrin complexes consist of a square planar MN4 core. The periph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
