Benzannulation

Kotha, Sambasivarao; Misra, Shilpi; Halder, Somnath

doi:10.1016/j.tet.2008.09.004

Cited by 141 publications

(32 citation statements)

References 68 publications

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“…Convergent benzannulation strategies 10 provide an exceptionally attractive approach for the regiocontrolled construction of multiply substituted benzenoid aromatic systems. Our laboratory has developed two complementary benzannulation strategies 5,11,12 based on the reaction of alkynes and vinylketenes, 13 and recently we have extended this chemistry to include ynamides as benzannulation partners in tandem benzannulation/cyclization strategies leading to several classes of polycyclic carbocyclic and heterocyclic compounds.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Highly Substituted Quinolines via a Tandem Ynamide Benzannulation/Iodocyclization Strategy

2015

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A two-stage "tandem strategy" for the regiocontrolled synthesis of very highly substituted quinolines is described. Benzannulation based on the reaction of cyclobutenones or diazo ketones with Npropargyl-substituted ynamides proceeds via a cascade of several pericyclic reactions to generate multiply substituted aniline derivatives. In the second stage of the tandem strategy, triflate derivatives of the phenolic benzannulation products undergo Larock cyclization upon exposure to iodine to form products that are further elaborated by methods such as palladium-catalyzed coupling to generate quinolines that can be substituted at every position of the bicyclic system.

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Section: Resultsmentioning

confidence: 99%

Synthesis of Highly Substituted Quinolines via a Tandem Ynamide Benzannulation/Iodocyclization Strategy

2015

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“…The extension of aromatic systems by annulation reactions is an effective way of extending smaller PAHs into larger graphene-like structures [83]. In this context multiple approaches have been devised.…”

Section: Annulation Reactionsmentioning

confidence: 99%

Strategies in Organic Synthesis for Condensed Arenes, Coronene, and Graphene

Tran‐Van

Wegner

2013

Polyarenes I

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Graphene-type structures are without doubt one of the most exciting carbon-based materials known. Although graphene is mostly prepared by physical methods (CVD, exfoliation), organic synthesis represents a powerful alternative to access graphene-type structures in a selective and reproducible manner. Although graphene has been hyped as a "new" material, the resemblance to polycyclic aromatic hydrocarbons (PAHs) offers a long history in organic chemistry on which all new endeavors are built. In this review we demonstrate the state-of-the-art of organic synthetic strategies for the preparation of graphene-type structures on selected examples.

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“…While there are many examples of transition-metal-promoted benzannulation reactions, there are relatively few examples that are catalyzed by Lewis acids. 11 Moreover, benzannulations involving acid-catalyzed cyclopropene…”

Section: Scheme 4 Ptsa-promoted Isomerization Of Cyclopropene 15mentioning

confidence: 99%

Acid-Catalyzed Ring-Opening Isomerizations of Cyclopropenes

Phun

Aponte-Guzman

2012

Synlett

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Acid-catalyzed cyclopropene cycloisomerizations are discussed as a means to generate ring systems. Herein, the recent results obtained in our group are contrasted with previous examples in the literature. Particular emphasis is placed on the mode of activation which, for our case, results in a different ring-opening mechanism than previously observed. The potential of the method as a tool for organic chemists is demonstrated by the synthesis of a host of benzo-fused heteroaromatic and heterobiaryl products.Cyclopropenes are highly strained carbocycles that have a range of reactivity beyond that of olefins, allenes, and alkynes. 1 While the presence of the double bond allows cyclopropenes to engage in addition reactions, liberation of the inherent ring strain enables cyclopropenes to undergo interesting ring-opening transformations. Cyclopropene cycloisomerizations represent one major class of these transformations that has garnered a tremendous amount of attention from synthetic chemists. 2 These reactions have been used as powerful synthetic tools due to their ability to construct carbo-and heterocyclic scaffolds with a high degree of molecular complexity and atom-economy. They have historically been promoted under thermal or photochemical conditions, however, over the past 50 years, cycloisomerizations promoted by transition metals have dominated the literature. 3 This is due to the fact that cyclopropenes have greater π-density than standard olefins, making them particularly attractive to π-philic transition metals. 4 For example, furans and pyrroles can be accessed from cycloisomerizations of 3-acyl-and 3-alkoxycarbonylcyclopropenes and cyclopropenyl imines using either Rh(II) or Cu(I) catalysts to generate metallocarbene species. 5 In contrast, few examples of protic or Lewis acid catalyzed cycloisomerizations have been documented in the literature. Herein, we discuss our contributions to this area within the greater and historical context of Brønsted and Lewis acid promoted cyclopropene ring-opening isomerizations. Historical examples are presented with particular emphasis on mechanistic details and insight.The earliest example of acid-mediated cyclopropene isomerization was reported in 1961 during the polymerization of sterculic acid (1, Scheme 1). 6 Heating sterculic acid in glacial acetic acid resulted in a complex mixture of four unsaturated allylic acetates. The purported mechanism involves protonation of the cyclopropene at either end of the π-system to generate the regioisomeric cyclopropyl cations 2 and 3. Ring-opening rearrangement then provides the pair of allylic cations 4 and 5, respectively. Acetic acid trapping at either end of both systems affords the four observed allylic acetates 6a-d.As part of their interest in the rearrangements of cyclopropyl cations, Breslow and co-workers demonstrated two examples of acid-promoted cyclopropene isomerizations. 7 In the first instance, diphenylcrotonolactone (8) was obtained when diphenylcyclopropene carboxylic acid 7 was treated with a protic acid (Sch...

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Benzannulation

Cited by 141 publications

References 68 publications

Synthesis of Highly Substituted Quinolines via a Tandem Ynamide Benzannulation/Iodocyclization Strategy

Synthesis of Highly Substituted Quinolines via a Tandem Ynamide Benzannulation/Iodocyclization Strategy

Strategies in Organic Synthesis for Condensed Arenes, Coronene, and Graphene

Acid-Catalyzed Ring-Opening Isomerizations of Cyclopropenes

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