3 edition of Reactions of quinone methides with varios nucleophiles found in the catalog.
Reactions of quinone methides with varios nucleophiles
Abbood Nasir Al-Khafaji
Thesis (Ph.D.) - University of Texas, 1966.
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Formation and Stability of Simple Quinone Methides. The parent p-quinone methide 1 and its relatives that contain the quinone methide functionality have long attracted the interest of discerning chemists. 1 can be thought of as a formally neutral benzylic carbocation at . Thieme E-Books & E-Journals. Abstract. This review summarizes recent advances in catalytic asymmetric reactions of o-quinone methides, an important family of species for organic the past decade, various catalytic systems have been developed for these reactions.
Second order rate constants for reactions of 4,4′-dimethylaminobenzhydrylium cations with amines and other nucleophiles in water define a scale of nucleophilicity (N+′′ = log k + ). The N+′′ scale can be extended by linking directly to an established N+ scale based on reactions of methyl vinyl pyridiniumCited by: 6. Silicon nucleophiles represent a class of important organometallic species for silicon–carbon, silicon–silicon, and silicon–boron bond formation reactions in synthetic chemistry . Conventionally, the generation of silicon nucleophiles is accomplished by reactions of chlorosilanes with alkali metal (K, Na, Li), reactions.
para ‐Quinone methides (p ‐QMs) are naturally occurring molecules with two electronically different exocyclic conjugate substituents in their structure, carbonyl and methylidene, which gives them a pronounced reactivity owing to the polarization of the molecule. By attack of nucleophiles in the terminal carbon exocyclic double bond, they. addition of a nucleophile. Reactivity of Quinone Methides Quinone methides can be thought of as charge separated carbocations  as depicted in Scheme 2. Effective charges have been calculated for each position of the most simple p-quinone methide structure according to the Hückle Molecular Orbital (HMO) model. The effective charge.
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Nucleophile addition to a quinone methide is formally a Michael addition reaction. However, an important difference between 1,6-addition of nucleophiles to p-quinone methides and conventional Michael addition reactions is the aromatization of the cyclohexadiene ring that accompanies this by: Reactions with nucleophiles 2 Use in diastereoselective synthesis 4 Intramolecular cyclization reactions 5 Radical cyclization reactions 5 Cycloaddition reactions 6 Biological activity of p-quinone methides 6 p-Quinone methide-based dyes 8 p-Quinone methides as organometallic ligands 9.
For the construction of these scales, rate consts. for the reactions of benzhydrylium ions (aryl2CH+) and structurally related quinone methides with nucleophiles have been measured and correlated by the equation lg k(20°) = sN(E + N), which yields abs.
rate consts. k (L mol-1 s-1) from one parameter for electrophiles (the electrophilicity E) and two for nucleophiles (the nucleophilicity parameter N and the Author: Andreas Eitzinger, Robert J.
Mayer, Nathalie Hampel, Peter Mayer, Mario Waser, Armin R. Ofial. quinone methide. However, pyrone quinone methide has not received practically any attention.
CYCLOADDITION REACTIONS OF COUMARIN QUINONE METHIDE One of the widely studied heterocyclic o-quinone methides is the 3-methylene-2,4-chromandione, 2. This quinone File Size: KB.
reactions with a variety of nucleophiles to generate substituted catechols. The reaction leads to 1,4-adduct of nucleophiles on the ring and ends up with the re-aromatization of the quinone nucleus.
Quinones can Reactions of quinone methides with varios nucleophiles book with water forming 1,4-addition by: the generation and reactions of quinone methides 69 increase in charge at the benzylic carbon leads to a large increase in the react ivity of this carbon with nucleophilic reagents that is consis.
The SmI 2 acts as a reducing agent, and the mechanism of the cyclization reaction is thought to involve the reduction of the quinone methide to afford a radical anion/dianion, which then undergoes ring closure.
96 Angle et al. have also used quinone methides generated by oxidation of phenols in conventional cyclization reactions, where the quinone carbon reacts as an electrophile with tethered nucleophiles. They react very rapidly with nucleophiles and undergo eﬃcient Diels–Alder reactions with electron-rich ole ns.
Expansive reactivity of the o-QM can be used in the linchpin reaction for the construction of various natural products.3 Compared to carbocations, carbanions, radicals, carbenes, nitrenes and so forth, ortho-quinone methides are relative. In continuation of our work on aromaticity driven 1,6-conjugate addition reaction on cyclohexadienone derivative 3 which serves as a versatile surrogate for p-quinone methide, we herein report: (i) bis-addition products of active methylene containing C-nucleophiles such as 1,3-diketones, diesters and ketoesters to 3 to obtain diarylpropanes and (ii) an interesting halophilic dimerization by: 1.
Question: O-Quinone Methides Are Very Reactive Electrophiles That Will React Instantly With Even Weak Nucleophiles Like Water. They Are Made In Situ In The Presence Of A Nucleophile And Undergo 1,4-addition And Inverse Diels-Alder Reactions (what's That?!). ConspectusAn ortho-quinone methide (o-QM) is a highly reactive chemical motif harnessed by nature for a variety of purposes.
Given its extraordinary reactivity and biological importance, it is surprising how few applications within organic synthesis exist. We speculate that their widespread use has been slowed by the complications that surround the preparation of their precursors, the harsh Cited by: A new family of CF 3 ‐containing para ‐quinone methides (CF 3 ‐QMs) was systematically investigated for its suitability in organic synthesis.
Addition of different nucleophiles gives access to target molecules with a benzylic CF 3 ‐containing stereogenic center straightforwardly. The electrophilicity parameter E of the prototypical CF 3 ‐QM 2,6‐di‐tert ‐butyl‐4‐(2,2,2.
The general reactivity of the p-quinone methides of interest to us was explored by subjecting these compounds to reaction with a range of nucleophiles (bases, Grignard reagents and alcohols).
A range of aryl Grignard reagents were reacted with the p-quinone methides, with the main product isolated in almost all cases being the aryl-coupled 1,2 Author: Jana Heloïse Taljaard. The quinonoid nucleus is very reactive and unstable.
Hence, it exhibits rapid Michael-1,4-addition reactions with a variety of nucleophiles to generate substituted catechols. The reaction leads to 1,4-adduct of nucleophiles on the ring and ends up with the re-aromatization of the quinone by: Since only p-quinone methides are typically associated with catecholamines, the rest of the article will deal with the reactions of these novel intermediates and no aspect of o-quinone methide chemistry will be discussed.
Quinone methides are extremely unstable and by: both nucleophiles and electrophiles. Its reactions, moreover, usually generate an aromatic phenol ring, and this provides a considerable driving force that adds to quinone methide reactivity.
Quinone methides have consequently become useful reaction intermediates with wide applications in organic. Intramolecular trapping of the quinone methides with an olefin led to the syntheses of several analogs of tetrahydrocannabinols.
ortho -Quinone methides, generated by treatment of the 2-phenyl-4 H -1,3,2-benzodioxaborins with a Lewis acid, react with various nucleophiles to give the corresponding 1,4-addition by: Quinone methides are cross-conjugated rather than aromatic. Nucleophilic addition at the exo-cyclic double bond will result in rearomatisation, making such reactions highly favourable.
As a result quinone methides are excellent Michael acceptors, react quickly with nucleophiles and can be easily reduced. Ortho‐quinone methides (o‐QMs) feature a particularly reactive 4π‐system and have increasingly been exploited as versatile synthetic intermediates for the construction of complex heterocycles.
11 In recent years, we and others have meticulously developed Brønsted acid catalyzed reactions of o‐QMs with a wide range of typically 2π Cited by: 1. This review summarizes recent advances in catalytic asymmetric reactions of o-quinone methides, an important family of species for organic synthesis.
In the past decade, various catalytic systems. One class of acceptor molecules that turned out to be highly versatile are p-quinone methides (p-QMs; 2). 14 These easily accessible and reasonably electrophilic 15 compounds have recently emerged as outstanding acceptors to access high levels of structural complexity upon reaction with different (pro)-nucleophi17 and we reasoned that.The reactions have proved to be successful on all of the amine salts.
Mechanistic understanding on the formation of high energy quinone methides and optimization of the reactions for their formation is currently still in progress.
Reaction testing with other nucleophiles will continue as well.In this sense, those are prone to undergo the attack of nucleophiles in the terminal carbon exocyclic double bond, behaving as vinylogous electrophiles and generating 1,6‐addition products.
In this context, in the last few years the development of catalytic approaches for 1,6‐nucleophilic addition reactions involving p ‐QMs has attracted Author: Carolina G. S. Lima, Fernanda P. Pauli, Dora C. S. Costa, Acácio S. de Souza, Luana S. M. Forezi, Vi.