One‐Pot Sequential Propargylation/Cycloisomerization: A Facile [4+2]‐Benzannulation Approach to Carbazoles

Reddy, Chada Raji; Valleti, Reddi Rani; Dilipkumar, Uredi

doi:10.1002/chem.201503496

Cited by 57 publications

(7 citation statements)

References 106 publications

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“…On the contrary, propargylic alcohols have extensively served as suitable substrates with a wide range of electrophiles and nucleophiles in the synthesis of numerous heterocyclic and carbocyclic compounds in recent years . In a continuation of our work using 1-arylpropargylic alcohols, herein we wish to report a novel one-pot [3 + 3] annulation of indole-2-carbonyls with 1-aryl propargylic alcohols for the synthesis of corresponding 3-hydroxycarbazoles via uninterrupted sequence involving propargylation and hydroxylative benzannulation reactions (Scheme b). To the best of our knowledge, a strategy that installs the hydroxyl group externally at the third position on the carbazole during the annulation (hydroxylative benzannulation) has not been reported to date.…”

supporting

confidence: 67%

One-Pot Assembly of 3-Hydroxycarbazoles via Uninterrupted Propargylation/Hydroxylative Benzannulation Reactions

et al. 2020

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A novel strategy for the synthesis of 3-hydroxycarbazoles involving the consecutive propargylation/palladium-catalyzed hydroxylative benzannulation of indole-2-carbonyls with propargylic alcohols has been exploited. This one-pot procedure leads to a wide range of substituted 3-hydroxycarbazoles in high yield with a broad substrate scope. The method was further extended to access furano-carbazole derivatives from dialkynols via tandem annulations.

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confidence: 67%

One-Pot Assembly of 3-Hydroxycarbazoles via Uninterrupted Propargylation/Hydroxylative Benzannulation Reactions

et al. 2020

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“…An efficient the BF 3 ⋅Et 2 O and DBU‐promoted synthesis of indole‐based [4]helicenes 103 – 105 through the [4+2]‐cycloaddition of 2‐aryl/heteroaryl indoles 100 with 1,3‐diphenylprop‐2‐yn‐1‐ol 101 has been elaborated (Scheme 28). [82] A plausible reaction pathway (Scheme 29) includes Lewis acid‐catalyzed C(3)‐propargylation of the starting indole 100 affording intermediate B via carbenium ion A . DBU‐induced isomerization of alkyne B provides allene C .…”

Section: Metal‐free Synthesesmentioning

confidence: 99%

Alkyne‐Based Syntheses of Carbo‐ and Heterohelicenes

Gulevskaya

Tonkoglazova

2022

Adv Synth Catal

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[n]Helicenes are polycyclic aromatic molecules in which n ortho‐condensed benzene or other aromatic rings give rise to helical chiral and highly conjugated structures. The unique screw shape, helically extended π‐system and intriguing electronic and chirooptical properties of these molecules have attracted scientific interest for decades. The applications of helicenes have now expanded into several fields including material science, nanoscience, biochemistry, supramolecular and polymer chemistry. Despite the great theoretical and practical interest in helicenes, their synthesis remains a challenge. Among synthetic approaches to helicenes, alkyne cyclizations have great potential, since carbon‐rich high‐energy alkynes can form aromatic rings via cycloisomerizations. These processes are atom‐economic. In addition, alkyne reactions are highly favorable thermodynamically. This review focuses on alkyne‐based syntheses of carbo‐ and heterohelicenes (2000–2022). These syntheses are obviously multistage. In the review, they are systematized in terms of the key step leading to the formation of a helical shape. The methods are grouped into two categories: (a) metal‐free syntheses and (b) transition‐metal‐catalyzed syntheses. This division is very arbitrary, since catalytic Sonogashira and Suzuki‐Miyaura reactions and others are often used to prepare starting materials in the syntheses of the first group. Most of the publications on the topic are related to transition‐metal‐catalyzed syntheses of helicenes.

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“…Reddy and co‐workers demonstrated a new route to highly substituted carbazoles 217 / 220 that involved the tandem reaction of 2‐alkenyl/aryl indoles 215 with 1‐aryl/heteroaryl propargylic alcohols 216 or aldehydes 218 through BF 3 ⋅ Et 2 O‐catalyzed C3‐propargylation, followed by DBU‐induced cycloisomerization and 1,3,5‐triene electrocyclization (Scheme ) . This transformation tolerated a wide range of 2‐alkenyl/aryl indoles and 1‐aryl propargylic alcohols and gave the products in moderate‐to‐good yields.…”

Section: Dbu‐mediated Benzannulation Reactionsmentioning

confidence: 99%

Recent Progress in Transition‐Metal‐Free, Base‐Mediated Benzannulation Reactions for the Synthesis of a Diverse Range of Aromatic and Heteroaromatic Compounds

et al. 2018

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Benzene and itsderivativesare the most abundant substructures of several interesting classes of compound, such as bioactive molecules. Owing to their importance, the development of methods for their constructionh as attracted considerable attention.H owever,t he regioselectives ynthesis of polysubstituted aromatic and heteroaromatic compounds by using aromatic substitution is challenging, because it provides derivatives with restricted substitution patterns. Therefore, the benzannulation reaction-the assembly of benzene derivatives from acyclicp recursors-constitutes as uperior and highly versatile approach to polysubstituted aromatic and heteroaromatic compounds,a nd variouse fficient benzannulation reactions have been reported.R epresentative examples include Cs 2 CO 3 , t-BuOK,a nd DBU-catalyzed reactions for the construction of valuableb enzene derivatives. The central objective of this Focus Review is to highlight base-mediated benzannulation reactions under transitionmetal-free conditions for the construction of aromatic and heteroaromatic compounds.[a] Dr.Recently,P an and co-workers investigated the K 2 CO 3 -catalyzed cascade benzannulation reaction of b-keto sulfones 1 with acetylene ketones 2 by using 30 %m ol K 2 CO 3 without other additives,w hich afforded new sulfonylbenzene derivatives 3 in good yields through ab enzannulation reaction (Scheme 1a). [18] Av ariety of electron-donating ande lectron-withdrawing groups were well-tolerated under the optimized reaction conditions. The proposed reactionpathway proceeded through se-quentialM ichael addition, intramolecular cyclization, hydrogen abstraction, and dehydration reactions (Scheme 1b).Scheme55. Synthesis of unsymmetrical biaryls from the annulation/aromatizationr eactionsof1 ,4-pentanedienes with nitroalkanes.Scheme56. DBU-promoted [5+ +1] annulation reaction of a-alkenoyl ketene-S,S-acetalswith nitroalkanes.

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One‐Pot Sequential Propargylation/Cycloisomerization: A Facile [4+2]‐Benzannulation Approach to Carbazoles

Cited by 57 publications

References 106 publications

One-Pot Assembly of 3-Hydroxycarbazoles via Uninterrupted Propargylation/Hydroxylative Benzannulation Reactions

One-Pot Assembly of 3-Hydroxycarbazoles via Uninterrupted Propargylation/Hydroxylative Benzannulation Reactions

Alkyne‐Based Syntheses of Carbo‐ and Heterohelicenes

Recent Progress in Transition‐Metal‐Free, Base‐Mediated Benzannulation Reactions for the Synthesis of a Diverse Range of Aromatic and Heteroaromatic Compounds

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