Chemical behavior of o-bis(phenylethynyl)benzene toward some electrophilic and nucleophilic reagents

Whitlock, H. W.; Sandvick, P. E.; Overman, Larry E.; Reichardt, Paul B.

doi:10.1021/jo01256a023

Cited by 55 publications

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“…The cyclization of enediynes can also be induced by the action of chemical reagents: lithium metal [16,17], radicals [18][19][20][21], electrophiles [16,22,23], transition metal complexes [24], organolithium compounds [16], and other anionic nucleophiles [25][26][27][28][29]. Most of the listed initiators promote 5-exo-dig carbocyclization of the enediynes with the formation of fulvenes (Scheme 3a [16]). On the other hand, nucleophilic attack on the enediyne substrate leads to 6-endo-dig carbocyclization (cycloaromatization) (Scheme 3b [28]).…”

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“…On the other hand, nucleophilic attack on the enediyne substrate leads to 6-endo-dig carbocyclization (cycloaromatization) (Scheme 3b [28]). The only exception is butyllithium, whose reaction with 1,2-bis(phenylethynyl)benzene produces benzofulvene derivatives (Scheme 3c [16] Examples of the heterocyclization of enediynes are not numerous and were found in the last decade. As a rule, such cyclizations are of the cascade type and are initiated by attack of an external anionic nucleophile or a nucleophilic group present in the molecule at one of the C≡C bonds of the enediyne.…”

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Nucleophilic cyclizations of enediynes as a method for polynuclear heterocycle synthesis

Gulevskaya

Tyaglivy

2012

Chem Heterocycl Comp

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In this review, data on the heterocyclization of enediynes, initiated by attack of an external anionic nucleophile or a nucleophilic group present in the molecule at the C≡C bond of the enediyne, are summarized.Today, the chemistry of acetylenes is experiencing its new birth. Effective methods for the synthesis of acetylenes based on the transition metal catalyzed cross-coupling of organic halides and triflates with 1-alkynes [1], alkynylboronic acids [2], alkynylstannanes [3] have been developed. The acetylenes that became accessible are used successfully for the synthesis of various carbo-and heterocyclic compounds [4][5][6][7][8][9]. In the general case addition of a nucleophilic group to a carbon-carbon triple bond leads to a hetero-ring closure according to Scheme 1, and here the formation both of endo-dig cyclization products and of heterocycles with an exocyclic C=C bond (exo-dig cyclization) is possible: exo-digR Nu X R Nu = NH, O, S, etc.; X = H or other leaving groupThe interest of researchers in the chemistry of acetylenes is also due to the discovery of a whole family of antibiotics containing a cis-3-hexene-1,5-diyne fragment in their structures and therefore called enediyne antibiotics [10][11][12][13][14]. When heated or irradiated the enediynes undergo a Bergman cyclization; they close to 1,4-arynes, which are converted in the presence of suitable donors of hydrogen atoms or other free radicals into the corresponding arenes (Scheme 2) [15]. It is supposed that the mechanism of biological action of enediyne antibiotics is based on this rather exotic transformation. At the biological level the role of hydrogen atom donor is played by a DNA molecule that leads to its destruction. This determines not only the antibacterial, but also the antiviral and anticancer activity of the enediyne antibiotics.

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Nucleophilic cyclizations of enediynes as a method for polynuclear heterocycle synthesis

Gulevskaya

Tyaglivy

2012

Chem Heterocycl Comp

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“…[4] Während die thermische Cyclisierung zu 3 aufgrund ihrer hohen Aktivierungsbarriere (ca. 40 kcal mol À1 mit UBS-B3LYP6-31G*) ungünstig ist, erhält man Pentafulvenderivate bei Reaktionen von Verbindungen wie 1 mit Elektrophilen (mit Brom entsteht 4 und nicht 5, Schema 1), [5][6][7] Carbanionen [6] oder Radikalen. [8] Somit sind die thermischen und reagenskontrollierten Reaktionen von 1 komplementär, und basierend auf bekannter Acetylenchemie gelingt die Synthese neuer kohlenstoffreicher Verbindungen.…”

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“…[11] Die vorliegende Arbeit beschäftigt sich daher mit dieser und ähnlichen Reaktionen, die Benzopentafulvene durch regioselektive, elektrophile Cyclisierungen liefern. [6,7,12] Überraschenderweise liegen keine vollständigen spektroskopischen Daten zu Dibromstilben (7) vor. Eine Quelle gibt ein 1 H-NMR-Spektrum für (E)-7 an, dessen Konfiguration durch eine Kristallstrukturanalyse bestätigt wurde, [13] und an anderer Stelle wird über die Verschiebungen von 13 C-NMR-Signalen für (E)-7 [14] berichtet, die wir hingegen (Z)-7 zuordnen.…”

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“…Die geringe Selektivität der Bromaddition deutet auf einen offenen kationischen Übergangszustand hin. [14] Die elektrophile Cyclisierung von 1 zu 4 (Schema 3) wird durch die Bildung des konjugierten Kations 10 erklärt; [6] die Cyclisierung zum Sechsring ergäbe dagegen ein höchst instabiles Naphthylkation. Beide Isomere von 4 können durch fraktionierende Kristallisation getrennt werden: Die Konfiguration des Hauptprodukts (E)-4 (> 80 %) wurde durch eine Kristallstrukturanalyse bestätigt.…”

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Fulvene aus Endiinen: Regioselektive elektrophile Domino‐ und Tandemcyclisierungen von Eninen und Oligoinen

2003

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Synthetic Applications of Phosphoryl‐Stabilized Anions

1977

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The successful synthesis of a wide variety of unsaturated compounds by treatment of phosphoranes with carbonyl compounds (the Wittig reaction) has stimulated the search for other synthetic methods that employ organophosphorus reagents. One of the most fruitful results has been the discovery that phosphoryl‐stabilized carbanions have wide applicability in the preparation of unsaturated compounds and offer significant advantages over conventional procedures. This review discusses the chemistry of carbanions stabilized by delocalization of their negative charge by means of a P(O) group. Carbanions obtained by treating phosphine oxides, phosphinates, and phosphonates, with a base have been explored in depth. In particular, the phosphonates have found great popularity because of their availability and ease of application. The use of Wittig‐type reagents in synthesis has been reviewed and is not mentioned except by way of comparison. Carbanions prepared from phosphinates have no known advantage over those prepared from phosphonates or phosphine oxides. Those carbanions obtained from phosphine oxides will be considered here only in the way of comparison. Anions that have their negative charge located on an atom adjacent to a P(O) group gain stability owing to delocalization of the charge through the phosphoryl group. Although the exact nature of the delocalization is not well defined, the ability of phosphorus to become pentacovalent by use of its d orbitals is undoubtedly a contributing factor. It should be noted that the P(O) group is generally not so effective as the carbonyl group in stabilizing a negative charge. If other stabilizing groups are not present, formation of P(O)‐stabilized carbanions generally requires more basic conditions than does the removal of a proton from a carbon atom alpha to a carbonyl group. Horner and co‐workers were the first to investigate the synthetic utility of P(O)‐stabilized carbanions. The utility of phosphonate carbanions as synthetic intermediates was expanded by the discovery that, as olefin‐forming reagents, phosphonates have certain advantages over both phosphoranes and phosphine oxides. As a result, the method has found favor because of the availability of reagents, ease of workup, and convenient reaction conditions. In particular, the reactivity of phosphonate carbanions has been taken advantage of in numerous ways. As indicated by a number of reviews, these carbanions have become one of the most frequently employed organophosphorus reagents. The utility of phosphoryl‐stabilized anions is apparent from the variety of materials that can be prepared by suitable structural modifications. Besides simple monoolefins and polyenes, a partial list would include allenes, unsaturated amides, aldehydes, esters, sulfides, sulfones, and nitrogen compounds such as imines, isocyanates, and ketenimines. In addition to their convenience for introducing unsaturation, these stabilized anions offer routes to cyclopropanes and heterocyclic systems. In this chapter, reactions that are of unusual interest are discussed separately; more routine reactions are included only in the tabular survey. Olefin formation by means of phosphonate carbanions has been referred to as the Horner‐Emmons or Wadsworth‐Emmons modification of the Wittig reaction, whereas the use of phosphine oxide or phosphinate carbanions is generally referred to as the Horner modification. In order to prevent confusion and to avoid misdirecting credit, proper names are omitted and the synthesis of an olefin by phosphonate carbanions is termed phosphonate‐olefin formation. Likewise, the term phosphine oxide‐olefin formation is employed where appropriate.

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Chemical behavior of o-bis(phenylethynyl)benzene toward some electrophilic and nucleophilic reagents

Cited by 55 publications

References 1 publication

Nucleophilic cyclizations of enediynes as a method for polynuclear heterocycle synthesis

Nucleophilic cyclizations of enediynes as a method for polynuclear heterocycle synthesis

Fulvene aus Endiinen: Regioselektive elektrophile Domino‐ und Tandemcyclisierungen von Eninen und Oligoinen

Synthetic Applications of Phosphoryl‐Stabilized Anions

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