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2,3-Wittig Rearrangement
The [2,3]-Wittig rearrangement is the transformation of an allylic ether into a homoallylic Alcohol (chemistry), alcohol via a concerted, pericyclic reaction, pericyclic process. Because the reaction is concerted, it exhibits a high degree of stereocontrol, and can be employed early in a synthetic route to establish stereochemistry. The Wittig rearrangement requires strongly basic conditions, however, as a carbanion intermediate is essential. 1,2-Wittig rearrangement, [1,2]-Wittig rearrangement is a competitive process. Introduction [2,3]-Sigmatropic rearrangements occur for a variety of groups X and Y (see below). When X is a carbanion and Y an alkoxide, the rearrangement is called the [2,3]-Wittig rearrangement and the products are pent-1-en-5-ols. The [1,2]-Wittig rearrangement, which produces isomeric pent-5-en-1-ols, is a competitive process that takes place at high temperatures. Because of the high atom economy and stereoselectivity of the [2,3]-rearrangement, it has gained c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Allylic
In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, . In 1844, Theodor Wertheim isolated an allyl derivative from garlic oil and named it "". The term allyl applies to many compounds related to , some of which are of practical or of everyday importance, for example, allyl chloride. Allylation is any chemical reaction that adds an allyl group to a substrate. Nomenclature A site adjacent to the unsaturated carbon atom is called the allylic position or allylic site. A group attached at this site is sometimes described as allylic. Thus, "has an allylic hydroxyl group". Allylic C−H bonds are about 15% weaker than the C−H bonds in ordinary sp3 carbon centers and are thus more reactive. Benzylic and allylic are related in terms of structure, bond strength, and reactivity. Other ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Smiles Rearrangement
The Smiles rearrangement is an organic reaction and a rearrangement reaction named after British chemist Samuel Smiles. It is an intramolecular nucleophilic aromatic substitution of the type: where X in the arene compound can be a sulfone, a sulfide, an ether or any substituent capable of dislodging from the arene carrying a negative charge. The terminal functional group in the chain end Y is able to act as a strong nucleophile for instance an alcohol, amine or thiol. As in other nucleophilic aromatic substitutions the arene requires activation by an electron-withdrawing group preferably in the aromatic ortho position. In one modification called the Truce–Smiles rearrangement the incoming nucleophile is sufficiently strong that the arene does not require this additional activation, for example when the nucleophile is an organolithium. This reaction is exemplified by the conversion of an aryl sulfone into a sulfinic acid by action of ''n''-butyllithium: This particul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deprotonation
Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju.edu/hjakubowski/classes/ch331/protstructure/PS_2A3_AA_Charges.html, accessed 12/2/2020 The species formed is the conjugate base of that acid. The complementary process, when a proton is added (transferred) to a Brønsted–Lowry base, is protonation (or hydronation). The species formed is the conjugate acid of that base. A species that can either accept or donate a proton is referred to as amphiprotic. An example is the H2O (water) molecule, which can gain a proton to form the hydronium ion, H3O+, or lose a proton, leaving the hydroxide ion, OH−. The relative ability of a molecule to give up a proton is measured by its p''K''a value. A low p''K''a value indicates that the compound is acidic and will easily give up its proton to a b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxy-Cope Rearrangement
In organic chemistry, the oxy-Cope rearrangement is a chemical reaction. It involves reorganization of the skeleton of certain unsaturated alcohols. It is a variation of the Cope rearrangement in which 1,5-dien-3-ols are converted to unsaturated carbonyl compounds by a mechanism typical for such a ,3sigmatropic rearrangement. The reaction is highly general: a wide variety of precursors undergo the reorganization predictably and with ease, rendering it a highly useful synthetic tool. Further, production of the required starting material is often straightforward. The modification was first proposed in 1964 by Berson and Jones, who coined the term. The driving force is the formation of a carbonyl via spontaneous keto-enol tautomerization. : Base accelerates the reaction by 1010-1017, the anionic oxy-Cope rearrangement. : The formation of an enolate renders the reaction irreversible in most cases. History Sigmatropic rearrangements are useful organic synthesis. In an effort to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phenyl
In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6 H5, and is often represented by the symbol Ph. Phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen, which may be replaced by some other element or compound to serve as a functional group. Phenyl group has six carbon atoms bonded together in a hexagonal planar ring, five of which are bonded to individual hydrogen atoms, with the remaining carbon bonded to a substituent. Phenyl groups are commonplace in organic chemistry. Although often depicted with alternating double and single bonds, phenyl group is chemically aromatic and has equal bond lengths between carbon atoms in the ring. Nomenclature Usually, a "phenyl group" is synonymous with C6H5− and is represented by the symbol Ph or, archaically, Φ. Benzene is sometimes denoted as PhH. Phenyl groups are generally attached to other atoms or groups. For example, triphenylmethane (Ph3 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
