Classes Of Electrophiles Research Articles

Functionalization of Bis‐Diazaphospholene P–P Bonds with Diverse Electrophiles

Phosphorus‐sp3 or ‐sp2 carbon bonds are readily formed by the reaction of bis‐diazaphospholenes with several classes of electrophiles. These reactions result in cleavage of the phosphorus–phosphorus bond and formation of functionalized diazaphospholenes. The reactions proceed rapidly, without catalysis. Experimental evidence with aryl and alkyl halides suggests the intermediacy of radicals in some cases, however other evidence suggests either radical or polar mechanisms may be operative for certain substrates, with a dependence on reaction conditions. In three cases, the product aryl diazaphospholenes have been shown to transfer the aryl substituent to electrophiles. These results reveal that diazaphospholene dimers are potent participants in radical chemistry with organic substrates at room temperature without requiring chemical initiators.

1,2-Amino Alcohols via Cr/Photoredox Dual-Catalyzed Addition of α-Amino Carbanion Equivalents to Carbonyls.

Herein, we report the synthesis of protected 1,2-amino alcohols starting from carbonyl compounds and α-silyl amines. The reaction is enabled by a Cr/photoredox dual catalytic system that allows the in situ generation of α-amino carbanion equivalents which act as nucleophiles. The unique nature of this reaction was demonstrated through the aminoalkylation of ketones and an acyl silane, classes of electrophiles that were previously unreactive toward addition of alkyl-Cr reagents. Overall, this reaction broadens the scope of Cr-mediated carbonyl alkylations and discloses an underexplored retrosynthetic strategy for the synthesis of 1,2-amino alcohols.

Applications of Bifunctional Organocatalysts on ortho‐Quinone Methides

Abstractortho‐Quinone methides are important structures, having a cyclohexadiene core bearing an exocyclic alkylidiene and carbonyl functionality at the ortho‐position, and are widely used as essential intermediates in organic synthesis. These reactive intermediates are also used as important building blocks for the construction of a variety of heterocycles by hetero Diels‐Alder, electrocyclization reactions. Moreover, ortho‐quinone methides are a class of electrophiles, serving as Michael acceptors leading to conjugate additions with various nucleophiles. In general, ortho‐Quinone methides have transient existence and are highly reactive in nature. ortho‐Quinone methides have been generated in situ from stable precursors using either Brønsted acids or Brønsted bases. In the last few years, ortho‐quinone methides have been explored as imperative class of substrates in various bifunctional organocatalysts mediated asymmetric conjugate additions, cycloannulation, acyl‐transfer reaction, thiolation and hydrophosphination reactions. This review illustrates recent advancements of asymmetric transformations of ortho‐quinone methides with bifunctional H‐bonding organocatalysts.

C-H carbonylation: In situ acyl triflates ace it.

A simple palladium catalyst has mediated the facile formation of aroyl triflates — an extremely reactive class of electrophiles. These intermediates, generated in situ, enable the Friedel–Crafts acylation of traditionally unreactive arenes, addressing a significant gap in C–H carbonylation methodology.

Selective Lithiation, Magnesiation, and Zincation of Unsymmetrical Azobenzenes Using Continuous Flow.

A mild and general set of metalation procedures for the functionalization of unsymmetrical azobenzenes using a commercially available continuous-flow setup is reported. The metalations proceed with TMPLi under convenient conditions (0 °C, 20 s), and various classes of electrophiles can be used. With sensitive substrates, an in situ trapping metalation in which TMPLi is added to a mixture of the azobenzene and ZnCl2 or MgCl2·LiCl was very effective for achieving high yields.

Lewis acid activated synthesis of highly substituted cyclopentanes by the N-heterocyclic carbene catalyzed addition of homoenolate equivalents to unsaturated ketoesters.

Lewis acid activated synthesis of highly substituted cyclopentanes by the N-heterocyclic carbene catalyzed addition of homoenolate equivalents to unsaturated ketoesters.

Pd-catalyzed Cross-Coupling of α-(Acyloxy)-tri-n-butylstannanes with Alkenyl, Aryl, and Heteroaryl Electrophiles

Racemic and scalemic α-(acyloxy)-tri-n-butylstannanes undergo Pd-catalyzed cross-couplings with alkenyl/aryl/heteroaryl iodides, bromides, and triflates in moderate to good yields in THF at 45 °C. Simple aryl iodides and unprotected aza-arenes, two classes of electrophiles that typically react sluggishly, are also good substrates. Cross-couplings proceed with retention of configuration at the alkenyl and stannyl-substituted stereocenters.

Scaleable Preparation of Sensitive Functionalized Aromatics and Heteroaromatics via Directed Metalation Using tmpZnCl·LiCl

A range of functional aryl and heteroaryl zinc reagents were prepared in THF via directed zincation using the previously reported amide base tmpZnCl·LiCl. These metalation reactions were carried out on 50 mmol scale. Diverse sensitive functional groups such as a nitro group, an aldehyde, an ester, and a nitrile are tolerated. Furthermore, the resulting zinc intermediates show excellent reactivity towards various classes of electrophiles, e.g. Pd-catalyzed cross-coupling reactions or Cu-catalyzed acylations and allylations. In all cases, the metalation rates have been compared with those of the corresponding small-scale reactions (1−2 mmol). Moreover, the recovery of the valuable tmp-H from the aqueous phase has been demonstrated.

ChemInform Abstract: Chemoselective Reaction of Bifunctional Aldehydo Allylsilanes.

Abstract Aldehydes, such as 1 , are only the second class of electrophiles found to undergo chemoselective intermolecular reaction with enolsilanes, as opposed to intramolecular attack by the allylsilane.

Highly Enantioselective Reactions of Configurationally Labile Epimeric Diamine Complexes of LithiatedS-Benzyl Thiocarbamates

Substitution reactions that employ primary-carbamoyl-protected arylmethanethiols are described. The enantiodetermining step was found to occur in the post-deprotonation step as a dynamic thermodynamic resolution with a chiral bis(oxazoline) ligand. The configurationally labile lithium complexes were trapped with various electrophiles to yield different substitution products in good to excellent yields and enantiomeric excesses. The absolute configurations of the substitution products were determined, and the stereochemical pathway of the substitution reaction was elucidated for different classes of electrophiles. The temperature-dependent epimerization process was monitored by 1H and 6Li NMR spectroscopy.

Stereospecific Cross‐Coupling of α‐(Thiocarbamoyl)organostannanes with Alkenyl, Aryl, and Heteroaryl Iodides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Stereospecific Cross-Coupling of α-(Thiocarbamoyl)organostannanes with Alkenyl, Aryl, and Heteroaryl Iodides

Racemic and scalemic PTC-protected alpha-hydroxystannanes cross-couple with alkenyl/aryl/heteroaryl iodides in moderate to good yields using copper(I) thiophene-2-carboxylate (CuTC) in THF at or below room temperature. Simple aryl iodides and 1-iodocyclohexene, two classes of electrophiles that typically react sluggishly, are also good substrates. Cross-couplings proceed with retention of configuration at the alkenyl- and stannyl-substituted stereocenters.

The Phospha‐Michael Addition in Organic Synthesis

AbstractPhosphorus is essential for many reagents in organic synthesis, for ligands of late‐transition metals and for phosphono‐ and phosphanylamino acids, the latter being important isosteres of amino acids. Similar to the Michaelis–Arbuzov and the Michaelis–Becker reaction the phospha‐Michael addition, i. e. the addition of a phosphorus nucleophile to an acceptor‐substituted alkene or alkyne, certainly represents one of the most versatile and powerful tools for the formation of P–C bonds since many different electrophiles and P nucleophiles can be combined with each other. This offers the possibility to access many diversely functionalised products. With this article, we try to give an instructive overview of this reaction. The outline of this review is supposed to be rather general and it is its goal to make the reader familiar with reactivity principles which are common to the different classes of electrophiles and/or P nucleophiles. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Antimutagens and anticarcinogens: A survey of putative interceptor molecules

In this review recent publications are cited for a number of antimutagens. The molecules surveyed are potential or proven "desmutagens" or "interceptors." These are biologically prevalent or synthetic molecules that are most often small metabolites proficient in binding to, or reacting with, mutagenic chemicals and free radicals. Many of this class of "blocking agents" are "soft" and "hard" nucleophiles with consequently varying abilities to react with particular classes of electrophiles, the major classes of direct-acting mutagens. Although they serve as a first line of defense against mutagens and carcinogens, many interceptor molecules are under-investigated with regard to their spectra of activity and their possible relevance to prophylaxis or treatment of human disease states.

Reduction electrochimique des derives carbonyles insatures : IX. Indanones et tetralones : electrolyses mixtes en presence d'electrophiles

It is shown that activated cyclic carbonyl compounds, such as tetralones and indanones, can behave in a particular manner when they are reduced in presence of electrophiles. Two classes of electrophiles were chosen : alkyl halides and carbon dioxide. The reactivity (alkylation and carboxylation) often depends on the nature of the activated ketone used as a substrate.

ChemInform Abstract: ORGANOBORANES AND ORGANOBORATE ANIONS, NEW CLASSES OF ELECTROPHILES AND NUCLEOPHILES IN ORGANIC SYNTHESIS

Chemischer InformationsdienstVolume 6, Issue 32 Organoelement Compounds ChemInform Abstract: ORGANOBORANES AND ORGANOBORATE ANIONS, NEW CLASSES OF ELECTROPHILES AND NUCLEOPHILES IN ORGANIC SYNTHESIS E. NEGISHI, E. NEGISHISearch for more papers by this author E. NEGISHI, E. NEGISHISearch for more papers by this author First published: August 12, 1975 https://doi.org/10.1002/chin.197532296AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume6, Issue32August 12, 1975 RelatedInformation

Organoboranes and organoborate anions. New classes of electrophiles and nucleophiles in organic synthesis

Presents some of the key features common to various reactions of organoboranes and interprets them in terms of a few common mechanistic schemes.