Benzannulation of arynes with dimethylacetonedicarboxylates via an insertion-fragmentation-Dieckman-aromatization cascade: Expeditious entry to naphthoresorcinols and binaphthoresorcinols

A simple route to 2,3-benzodiazepines from substituted indenes

Herein, we present a two-step approach for synthesizing 2,3-benzodiazepines from substituted indenes. This process involves oxidation of indenes to 1,5-diketones followed by their cyclocondensation with hydrazine hydrate. The optimized conditions for a wide range of substituted 2,3-benzodiazepines, including the well-known anxiolytic tofisopam, were investigated. A detailed mechanism for the cyclization of 1,5-diketones with hydrazine hydrate was established using 1H NMR kinetic experiments.

One-Flask, Telescoped Synthesis of Pyrano[3,2-b]indol-2-ones from O-Nitroynones and β-Ketoesters: Further Advancement to Functionalized Carbazoles

A new general strategy for accessing pyrano[3,2-b]indol-2-ones, a promising fused hybrid heterocyclic system, has been devised from o-nitroynones and β-ketoesters through a one-flask cascade process involving tandem Michael addition, intramolecular cyclization, and Cadogan-Sundberg reductive cyclization. The utility of this approach has been further amplified by leveraging the cycloaddition proclivity of the α-pyrone moiety in pyrano[3,2-b]indol-2-ones toward a concise entry to carbazoles. Illustrative synthesis of the carbazole natural products hyellazole and chlorohyellazole is also disclosed.

Practical Access to Fused Carbazoles via Oxidative Benzannulation and their Photophysical Properties

An aryne annulation strategy for the synthesis of fused carbazoles is developed using indolyl β-ketonitrile in a cascade manner. The reaction sequence involves aryne-mediated [2 + 2] cycloaddition cleavage and intramolecular Michael addition, followed by oxidation under transition-metal-free reaction conditions. Subsequently, conversion of benzo[b]carbazole-6-carbonitrile to carbazole quinone is observed upon prolongation of the reaction time. Furthermore, these materials exhibit high quantum efficiency, which promotes the light-emitting diode applications.

Arynes as synthetic linchpins towards the construction of diversely functionalized natural product skeletons

Arynes are a privileged class of reactive intermediates in synthetic organic chemistry, and their unusual reactivities have been the subject of engrossing research interest. Recently, there are many reports on novel aryne-based synthetic innovations as a linchpin approach to accomplish the total synthesis of structurally diverse natural products or their derivatives in a racemic and enantiopure fashion. This review provides an overview of the literature on synthetic strategies, employing arynes as crucial intermediates to construct architecturally intriguing bioactive natural products/derivatives in a period of 2019 to 2022. This study highlights the need to investigate the effective synthesis and search for new biological uses of highly functionalized natural product skeletons.

Cascade aryne insertion/vinylogous aldol reaction of vinyl-substituted β-keto/enol carbonyls

Cyclic and acyclic vinyl substituted β-keto/enol carbonyl substrates, on reaction with arynes, result in differentially substituted naphthyl carbocycles, hitherto difficult to synthesize with existing protocols. While the substitutions on the arynes have no role, the ring size of the cyclic β-keto/enol esters has a profound influence on the product formation.