Synthesis and Acid‐Catalyzed Cyclization of 2‐Alkenylstilbenes: a New Approach to the Substituted Indenes

A base‐catalyzed ring‐opening of 1‐benzylisochromans 1 firstly produced 2‐alkenylstilbenes 2 , which then underwent a mild acid‐catalyzed intramolecular cyclization to furnish 1,2‐disubstituted indenes 3 in high yields. Subsequently, a base‐catalyzed isomerization of the 1,2‐disubstituted indenes 3 afforded the more stable 2,3‐disubstituted indenes 4 in almost quantitative yields.     

A general and efficient synthesis of substituted fluorenes and heterocycle-fused indenes containing thiophene or indole rings utilizing a Suzuki-Miyaura coupling and acid-catalyzed Friedel-Crafts reactions as key steps

A general and efficient synthesis of fluorenes or heterocycle-fused indenes including 3-thia-cyclopenta[a]indenes, 9-thia-indeno[1,2-a]indenes, 5,6-dihydroindeno[2,1-b]indoles has been developed. This methodology is realized by a multistep protocol involving first preparation of ortho-formylbiaryls through Suzuki-Miyaura coupling of o-bromobenzaldehydes with arylboronic acids or the coupling of aryl halides with 2-formylbenzene boronic acid, this is followed by Grignard addition and Friedel-Crafts cyclization reactions catalyzed by Brønsted or Lewis acid to form the desired fluorene or indene rings. The method offers several advantages such as high yields, high selectivities, mild reaction conditions, easily accessible starting materials, and so on.     

One-pot synthetic routes to multiply substituted indene derivatives by hydrolysis of zirconocene-mediated intermolecular coupling reactions of aromatic ketones and alkynes

Two one-pot multicomponent synthetic methods for highly substituted indenes are described. The intermolecular coupling of aromatic ketones with alkynes on low-valent zirconocene species generates oxazirconacyclopentenes, which upon hydrolysis with 20% HCl for 3 h afforded indene derivatives in good to excellent yields. Similarly, the pair-selective coupling of two identical or different alkynes bearing at least one aromatic substituent formed zirconacyclopentadienes. Quenching of the reaction mixture with concentrated H(2)SO(4) also results in the formation of highly substituted indenes in high yields.     

Synthesis of Substituted Indenes from Isovanillin via Claisen Rearrangement and Ring‐Closing Metathesis

A new synthesis of substituted indenes was studied. Based on Claisen rearrangement, Wittig reaction and ring‐closing metathesis (RCM), a series of substituted indenes was synthesized from isovanillin in good yields.     

Reactions of arylacetylenic compounds with arenes in the presence of aluminum halides

Conjugated arylacetylenic ketones and aldehydes, propargyl-type alcohols, and arylacetylenes reacted with arenes in the presence of AlBr₃ or AlCl₃ as catalyst to give substituted indenes. 3-Arylpropynoic acids under analogous conditions gave rise to 3,3-diarylindan-1-ones, while the corresponding methyl esters were converted into methyl 3,3-diarylprop-2-enoates. The key intermediates in the transformations of acetylenic ketones and aldehydes and propargyl-type alcohols into indene derivatives are resonance-stabilized propargyl—allenyl cations -C≡ C-C⁺ ? -C⁺=C=C which reacted with one of the resonance structures to give isomeric indenes, depending on the substituent nature.     

Intramolecular Substitution Reaction of Alkylidene‐Lithium Carbenoids: Regioselective Synthesis of Indenes

Intramolecular substitution reaction of geminal dibromo alkenes proceeds to afford indenes, dihydronaphthalenes, dihydrofurans, and dihydropyran via in situ generated lithium alkylidene carbenoids, which have a carbon or oxygen nucleophilic moiety. This reaction provides a regioselective method for the preparation of polysubstituted indenes.     

Palladium-catalyzed cycloisomerizations of diarylacetylenes: synthesis, structures, and physical properties of highly substituted naphthalenes and 8,8 a-dihydrocyclopenta[a]indenes

Depending on the electronic properties of their substituents, the major products generated by palladium‐catalyzed cycloisomerizations of diarylalkynes are either highly substituted 8,8a‐dihydrocyclopenta[a]indenes 3 or naphthalenes 4 . The structures of these compounds were verified by X‐ray crystallographic analysis. Many functional groups tolerated the reaction conditions evaluated in this study. The isotope‐labeled experiments indicated that added water has a critical role in forming both classes of compounds. The photophysical and electrochemical properties of cycloadducts 3 and their analogues were systematically studied and compared with computational predictions based on density functional theory. Dihydrocyclopenta[a]indenes 3 in either solid or liquid form display strong luminescence, whereas cyclopenta[a]indene 11 j is practically nonfluorescent. The functional groups directly attached to the backbone of compound 3 significantly influenced physical properties. The steric effect arising from the aryl substituents caused different luminescence phenomena, including aggregation‐induced and ‐enhanced emission.     

Asymmetric [3 + 2] annulations catalyzed by a planar-chiral derivative of DMAP

A planar-chiral DMAP derivative catalyzes an intriguing [3 + 2] annulation reaction of silylated indenes to produce diquinanes that bear three contiguous stereocenters (one quaternary and two tertiary).     

Tandem reaction of 3-hydroxyhexa-4,5-allenic esters: a novel access to diversely substituted 2H-pyran-2-ones and indenes

A highly efficient synthesis of diversely substituted 2H-pyran-2-ones and indenes through Br?nsted acid promoted tandem reaction of the readily obtainable 3-hydroxyhexa-4,5-allenic esters under extremely mild conditions has been developed.     

Regioselective 5‐endo‐dig Electrophilic Iodocyclization of Enediynes: A Convenient Route to Iodo‐substituted Indenes and Cyclopenta‐Fused Arenes

An efficient iodine‐mediated regioselective tandem approach for the synthesis of symmetric and asymmetric iodo‐substituted indenes and stereoselective cyclopenta [b]pyridine/thiophenes from easily accessible enediynes that proceeds by in situ formation of an iodonium intermediate followed by a regioselective 5‐endo‐dig cyclization has been described. The intramolecular electrophilic iodocyclization was selectively triggered by a distribution of electronic density along the alkyne bond. Subsequently, the iodo‐substituted indenes were diversified by employing palladium‐catalyzed cross‐coupling reactions and the coupled products were further confirmed by X‐ray crystallographic studies.     

Synthesis of 2-bromo-1-aryl-1H-indenes via a Ag(I) promoted domino 2π-electrocyclic ring-opening/4π-electrocyclization reaction of 1,2-diaryl substituted gem-dibromocyclopropanes

2-Bromo-1-aryl substituted indenes can be synthesized from 1,2-diaryl substituted gem-dibromocyclopropanes via a domino reaction sequence. The cascade reaction involves silver(I) promoted ionization and 2π-disrotatory electrocyclic ring-opening, followed by a 4π-conrotatory electrocyclic ring closing reaction of the allylic carbocation intermediate. Reaction conditions utilize silver tetrafluoroborate (AgBF₄) in dichloroethane at 65 °C. Selectivity effects for the electrocyclization were also studied. The 2-bromoindenes can be further functionalized using cross-coupling reactions, such as the Suzuki–Miyaura protocol. The alkene π-bond of the indenes can also be isomerized to give the thermodynamically more stable 2-bromo-3-aryl-1H-indene isomers using triethylamine in dichloromethane at room temperature.     

Fe(Ⅲ)催化的烯丙醇的Friedel-Crafts环化反应合成多取代茚

在FeCl3·6H2O催化下,多取代的烯丙醇可以顺利进行分子内Friedel-Crafts环化反应,以中等到优良的产率得到一系列多取代茚化合物,该反应操作简单、反应条件温和.产物结构经IR,1H NMR,13C NMR,HR MS及X射线单晶衍射分析确证.     

Efficient synthesis of 3-iodoindenes via Lewis-acid catalyzed Friedel-Crafts cyclization of iodinated allylic alcohols

A convenient BF(3).Et(2)O-catalyzed Friedel-Crafts cyclization of iodinated allylic alcohols is reported. The present reaction provides an efficient protocol to 3-iodo-1(H)-indene derivatives in good to high yields under mild conditions. Further, the iodoindene derivatives are valuable synthetic building blocks for elaboration of molecular complexity, such as in the construction of multiaryl substituted indenes by Suzuki coupling reaction.     

New method for the synthesis of indenes

A new two-step method was developed for the synthesis of 2-sulfonyl-substituted indenes from aromatic aldehydes. The reactions of 1-phenylsulfonyl-1-(trimethylsilyl)ethylene with ortho-lithiated derivatives of aromatic and heteroaromatic aldehydes afford conjugate addition products whose subsequent cyclization gives substituted 2-sulfonylindenes in preparative yields. The reactions of 2-(phenylsulfonyl)indenes with Grignard reagents were studied. It was shown that the sulfonyl group can be replaced in the presence of iron(iii) acetylacetonate.     

Photocatalytic Sulfonylcarbocyclization of Alkynes Using SEt as a Traceless Directing Group: Access to Cyclopentenes and Indenes

Cyclopentenes and indenes are important structural scaffolds in synthetic, medical, and material chemistry. Cyclization of alkynes via remote C?H functionalization is an appealing approach to construct these motifs due to its high efficiency and step-economy. Herein, a traceless directing group strategy was designed to reverse the regioselectivity of radical addition which enabled an unprecedented photocatalytic sulfonylcarbocyclization of terminal alkynes by forming C?C bond on inert C(sp³)?H bond. It offers a facile access to decorated cyclopentenes and indenes under mild conditions. The resultant products could be converted into a set of valuable molecular scaffolds, including a key intermediate of AM-6226. Mechanistic experiments suggest a radical cascade pathway comprising a Markovnikov-type sulfonylation, 1,5-hydrogen atom transfer, 5-endo-trig cyclization, and β-elimination. This study lays further groundwork for the use of anti-Baldwin 5-endo-trig radical cyclization in rapidly assembling five-membered carbocycles.     

Gold(I)‐Catalyzed Synthesis of Indenes and Cyclopentadienes: Access to (±)‐Laurokamurene B and the Skeletons of the Cycloaurenones and Dysiherbols

The formal (3+2) cycloaddition between terminal allenes and aryl or styryl gold(I) carbenes generated by a retro‐Buchner reaction of 7‐substituted 1,3,5‐cycloheptatrienes led to indenes and cyclopentadienes, respectively. These cycloaddition processes have been applied to the construction of the carbon skeleton of the cycloaurenones and the dysiherbols as well as to the total synthesis of (±)‐laurokamurene B.     

CuI-catalyzed tandem carbomagnesiation/carbonyl addition of Grignard reagents with acetylenic ketones: Convenient access to tetrasubstituted allylic alcohols

Highly functionalized tetrasubstituted allylic alcohols were prepared conveniently by CuI-catalyzed tandem carbomagnesiation/carbonyl addition of Grignard reagents with acetylenic ketones. The obtained allylic alcohols can be further transformed to polysubstituted indenes by intramolecular cyclization.     

Recent Advances in the Synthesis of Indanes and Indenes

Indanes and indenes are among the most important carbocycles. Many indane and indene derivatives have shown important pharmacological activities, and the indane and indene nuclei are structural motifs present in several natural products of biological relevance. In spite of their importance, only a few reviews on their preparation methods have appeared so far in the literature, the most recent ones being published about ten years ago. The present Review is aimed at filling this gap, presenting some of the most important and innovative approaches to indanes and indenes that have been published in the course of the last ten years (coverage: from 2005 to May, 2015).     

Ga(III)-catalyzed cycloisomerization strategy for the synthesis of icetexane diterpenoids: total synthesis of (+/-)-salviasperanol

[reaction: see text] A general approach to the tricyclic core of the icetexane natural products via the cycloisomerization of alkynyl indenes using GaCl(3) is presented. This strategy provides an efficient synthesis of the natural product salviasperanol and sets the stage for access to other members of this family of diterpenoids.     

Palladium-catalyzed synthesis of substituted cyclopentadienes and indenes from allylic esters

Various mono- and di-substituted cyclopentadienes have been prepared by palladium-catalyzed alkylation of allylic esters with cyclopentadienide and t-butyl-cyclopentadienide anions. The same procedure has been applied to the preparation of substituted indenes.