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The extended π-conjugated compounds 1 – 8 were synthesized by the benzannulation of the corresponding alkyne derivatives followed by Pd-catalyzed intramolecular cyclization. For the Pd-catalyzed intramolecular cyclization, microwave irradiation reduced the amount of the Pd catalyst and the reaction time. Moreover, this protocol can be achieved to prepare the extended and twisted π-conjugated molecule 19 , having anthracene, helicene, and picene skeletons. [Display omitted] • Synthesis of extended PHAs in a short step by benzannulation and intramolecular cyclization. • Improvement of reaction conditions of Pd-catalyzed C–H arylation by microwave irradiation. • Reaction mechanism of Pd-catalyzed C–H arylation depending on the substrate. • Applicable to extended and twisted π-conjugated molecule. [ABSTRACT FROM AUTHOR]

We report herein an original protocol to the indole nucleus, which could contribute to significantly expand the synthetic access to a heterocyclic moiety of undeniable paramount importance. The protocol consists in the construction of the benzene ring onto a pyrrole (benzannulation) starting from 2,3-dinitro-1,3-butadienes. This appealing, metal-free process characterized by high atom economy and mild reaction conditions allows to synthesize indoles possessing nitro group(s) on the benzene ring: a result which cannot be likewise easily obtained by exploiting most common pathways such as functionalization of a preformed indole or heteroannulation of a suitable benzene derivative. From a mechanistic point of view, a stepwise, ionic process is suggested by the identification of a pivot dihydroindole intermediate whose interception facilitates some selectivity in the preparation of different nitroindoles. Image 1 [ABSTRACT FROM AUTHOR]

The facile synthetic approach of coumarin derivatives has been described through Michael addition/cyclization/oxidative benzannulation using carbon-based solid sulfonic acid as the sustainable catalyst. The reaction proceeds in good to excellent yields in one-step from hydroxy-substituted chalcone, ethyl acetoacetate and amine. The utility of this transformation has been highlighted by its use for the construction of alkylaminobenzocoumarin, which was a new coumarin fluorescent molecular. [Display omitted] [ABSTRACT FROM AUTHOR]

We have achieved a simple, facile and three-component synthesis of C8 and C9 alkyl/aryl C7-hydroxydibenzopyrans-6-ones involving C3-acyl coumarins, selective active methylene compounds and some methyl ketones (reagent/solvent) under basic (K 2 CO 3) conditions. Overall, our method worked by benzannulation of the existing coumarins. In this work, we used the 2-NB group (2-NB = 2-nitrobenzyl) as a surrogate for C7–OH to engineer the construction of the ring C of the 3-hydroxydibenzopyran-6-ones. Subsequently, the photolabile 2-NB was removed under neutral conditions to reveal the C3–OH. [Display omitted] [ABSTRACT FROM AUTHOR]

A new route has been reported for the synthesis of densely oxygenated polycyclic aromatic compounds via cycloaddition approach. This strategy involves the Dötz benzannulation and Diels-Alder reaction as key steps. Naphthalene synthons required here were generated by Dötz benzannulation between aryl chromium carbene complexes and symmetrical internal alkyne. [ABSTRACT FROM AUTHOR]

BF 3 ·OEt 2 -mediated a one-pot tandem benzannulation of 4-alkynols 5 with oxygenated benzenes 4 affords 1-arylnaphthalenes 6 in good yields. The key synthetic route combines a facile double Friedel–Crafts electrophilic cyclization of 4-alkenols 5 followed by a sequential desulfonative aromatization. A plausible mechanism has been studied and proposed. [ABSTRACT FROM AUTHOR]

Sc(OTf) 3 -mediated one-pot benzannulation of oxygenated phenylacetic acids 3 with oxygenated benzenes 2 in the presence of Tf 2 O in MeCN at rt for 3 h afforded a series of polyoxygenated benzo[ g ]chrysenes 1 and naphthalenes 5 with moderate to good yields under the photolytic irradiation condition. The facile transformation proceeds by a cascade sequence starting with a double Friedel–Crafts acylation of skeleton 2 with 3 , followed by a double Scholl ring-closure and then, an O-acylation. [ABSTRACT FROM AUTHOR]

Abstract: An efficient and mild route to a series of benzo[b]thiophenes, benzo[b]furans, and dibenzofurans through gold-catalyzed benzannulation of 1-heteroarylalka-2,3-dienyl acetates was developed. Two possible pathways of this reaction involving gold carbene and aryl gold intermediates have been proposed on the basis of mechanistic studies. [Copyright &y& Elsevier]

Abstract: A novel, efficient, and powerful methyl mercaptoacetate triggered benzannulation reaction is described. The precursors are heterocyclic, aromatic or acyclic compounds bearing a carbonyl group at ortho position to an internal alkyne. The methodology does not require transition-metal catalysts and moreover it is general for the preparation of wide range of benzo-annelated heterocycles, naphthalenes and benzenes. [ABSTRACT FROM AUTHOR]

Abstract: A two-step strategy for the synthesis of benzo-fused indanes is outlined herein. The strategy draws on two independent methodologies: the tandem addition/fragmentation of vinylogous acyl triflates (VATs) and the intramolecular benzannulation of o-alkynylphenyl ketones. Reduction of this strategy to practice involves the use of aryltriazenes as masked aryl iodides; a synthetic equivalent of 2-iodophenyllithium is featured. Benzo-fused indanes are prepared efficiently and in high yield. [Copyright &y& Elsevier]

Abstract: The development of a formal synthesis of aflatoxin B2 is described, which utilizes a Dötz benzannulation reaction as a key step. [Copyright &y& Elsevier]

Abstract: (Trialkylsilyl)vinylketenes react with lithium ynolates to generate 3-(oxido)dienylketenes, which undergo rapid 6π-electrocyclization. The ultimate products of this benzannulation are highly substituted resorcinol monosilyl ethers, which are formed via a [1,3] carbon to oxygen silyl group shift. Further transformations of the benzannulation products are described providing efficient access to ortho-benzoquinones and benzofuran, benzoxepine, and benzoxocine ring systems. [Copyright &y& Elsevier]

Abstract: The AuCl-catalyzed benzannulation of ortho-alkynylphenyl ketones with benzenediazonium 2-carboxylate proceeded efficiently at 40°C in (CH2Cl)2 and a variety of anthracene derivatives, having a ketone group at 9-position, were produced in good to high yields. On the other hand, the reaction of ortho-alkynylbenzaldehydes with benzenediazonium 2-carboxylate afforded triptycyl ketones. The reactions most probably proceed through the formation of a zwitterionic intermediate by the gold-induced electrophilic cyclization of ortho-alkynyl(oxo)benzenes, followed by the cycloaddition of benzyne. In contrast, when the above reaction was carried out at rt in 1,4-dioxane, phthalazine derivative was produced without the generation of benzyne. [Copyright &y& Elsevier]

Abstract: An isomeric series of homologous crownophanes (i.e., macrocycles possessing structural features of crown ethers and cyclophanes) has been prepared via a concise and modular synthetic route. Macrocyclization is achieved in reasonable yield during the course of an enaminone-triggered benzannulation with bis(aryl ethynyl ketone) reaction partners. The crownophanes examined were active alkali cation binding agents in the gas phase, but failed to exhibit ionophoric properties in solution. On the basis of X-ray crystallographic analysis, it is concluded that the cyclophane framework of these macrocycles is too large and rigid to allow efficient interaction with the cations examined. [Copyright &y& Elsevier]

Efficient enantioselective syntheses of the functionalized phenol and diethynylcyclopentene moiety of the maduropeptin chromophore were achieved. Their CsF-mediated coupling yielded a sterically congested aryl propargyl ether. The subsequent intramolecular Sonogashira coupling reaction between the vinyl iodide and diethynyl groups occurred at the appropriate position to yield a macrolactam, which was accompanied by Pd-mediated enyne-yne benzannulation. [Copyright &y& Elsevier]

The formation of 1-acyl-2,2-diphenylcyclopropanes is performed under mild electrochemical conditions. These cyclopropane derivatives, through acid-catalyzed ring-opening, lead to γ,γ-diphenyl-β,γ-unsaturated carbonyl compounds which evolve into either substituted naphthalenes, or β-benzhydryl-α,β-cycloalkenones depending on the acyclic or cyclic nature of the intermediate allyl ketone. [Copyright &y& Elsevier]

An interesting and facile triflic acid catalysed annulation of α-aryl carbonyls with arylalkynes is presented for the regioselective synthesis of substituted naphthalenes. The annulation reaction involves a sequence of electrophilic attack of carbonyl on arylalkyne and benzannulation catalysed by triflic acid. The present catalyst effects this transformation at room temperature itself. Intramolecular version of the present Brønsted acid catalysis furnished compounds containing 1-arylnaphthalene core fused with ring systems in excellent yields. [Display omitted] [ABSTRACT FROM AUTHOR]