A New Method of Constructing Methyleneindene and Quinoline Frameworks from Methylenecyclopropanes

In this paper, we have established an operationally convenient protocol for the rapid construction of polysubstituted methyleneindene and quinoline derivatives under mild conditions. This new synthetic method is achieved through the conversion of acetyl-substituted methylenecyclopropanes with TsOH ⋅ H2O and ortho-amino-substituted methylenecyclopropanes with aromatic aldehyde and TsOH ⋅ H2O, respectively. A variety of transformations of the obtained products was demonstrated. The plausible reaction mechanisms were also proposed.

Metal-Free Construction of Multisubstituted Indolizines via Intramolecular Amination of Allylic Alcohols

An intramolecular amination of allylic alcohols is developed as an efficient and general access to biologically important multisubstituted indolizines and their variants. Two metal-free synthetic platforms including using aqueous hydrochloric acid solution as the solvent and p-toluenesulfonic acid as the catalyst have been established, enabling the divergent synthesis of these valuable compounds in high yields.

Ni-catalyzed arylation of alkynes with organoboronic acids and aldehydes to access stereodefined allylic alcohols

A new, efficient and practical method for the three-component arylative coupling of aldehydes, alkynes and arylboronic acids has been developed through nickel catalysis. This transformation provides diverse Z-selective tetrasubstituted allylic alcohols without the use of any aggressive oragnometallic nucleophiles or reductants. Moreover, benzylalcohols are viable coupling partners via oxidation state manipulation and arylative coupling in one single catalytic cycle. This reaction features a direct and flexible approach for the preparation of stereodefined arylated allylic alcohols with broad substrate scope under mild conditions. The utility of this protocol is demonstrated through the synthesis of diverse biologically active molecular derivatives.

TfOH-Promoted Reactions of TMS-Ethers of CF3-Pentenynoles with Arenes. Synthesis of CF3-Substituted Pentenynes, Indenes, and Other Carbocyclic Structures

Trimethylsilyl ethers of 1,5-diaryl-3-(trifluoromethyl)-pent-1-en-4-yn-3-oles [Ar-C≡C-C(CF₃)(OSiMe₃)-CH═CH-Ar'] in the superacid TfOH give rise to reactive conjugated CF₃-allylic-propargylic cations [Ar-C≡C-C⁺(CF₃)-CH═CH-Ar']. These species react with arenes in the presence of 1.5 equiv of TfOH forming regio- and stereoselectively E-1,1,5-triaryl-3-(trifluoromethyl)-pent-2-en-4-ynes [Ar-C≡C-C(CF₃)═CH-CHAr'(Ar″)] in good yields. In the excess of TfOH, these CF₃-pentenynes are further intramolecularly cyclized into CF₃-bicyclic dihydroanthracene derivatives ("helicopter"-like molecules). The CF₃-pentenynes may also react with arenes, as external nucleophiles, leading to CF₃-indenes. These two main reaction pathways depend on internal nucleophilicity of aryl substituents in CF₃-pentenynes and external nucleophilicity of aromatic molecules. Plausible cationic reaction mechanisms have been discussed. CF₃-bicyclic dihydroanthracene derivatives have been studied regarding their cytotoxicity and virus-inhibiting activity against influenza virus A/Puerto Rico/8/34 (H1N1) in MDCK cell line.

Regioselective trans-Carboboration of Propargyl Alcohols

Proper choice of the base allowed trans-diboration of propargyl alcohols with B₂(pin)₂ to evolve into an exquisitely regioselective procedure for net trans-carboboration. The method is modular as to the newly introduced carbon substituent (aryl, methyl, allyl, benzyl, alkynyl), which is invariably placed distal to the −OH group.

TfOH-promoted transformation of TMS-ethers of diarylsubstituted CF3-allyl alcohols with arenes into CF3-indanes

Novel synthesis of 1,3-diaryl-1-trifluoromethyl indanes, having predominantly a trans-configuration of aryl groups, was developed on the basis of the reaction of TMS-ethers of 2,4-diaryl-1,1,1-trifluorobut-3-en-2-ols with arenes in superacid TfOH.

Indium triflate catalyzed microwave-assisted alkenylation of methoxyphenols: synthesis of indenes and chromenes

In(OTf)3 catalyzed microwave-assisted alkenylation of methoxyphenols was investigated. Exclusive formation of either indenes or chromenes was observed depending on the position of the methoxy group on phenol. The structures of 1H-inden-4-ol derivatives (4a-e) and 4H-chromene derivatives (5a-j) were established by NMR ((1)H & (13)C) and high-resolution mass spectra, which were further supported by single crystal X-ray analysis of 4c and 5a.

A Tin(IV) Chloride Promoted Tandem C-O Bond Cleavage/Nazarov Cyclization/Nucleophilic Addition Reaction of 1,1-Disubstituted Allylic Ethers toward the Synthesis of Multisubstituted Indenes

A novel SnCl4-promoted tandem reaction toward multisubstituted indenes via a sequential C-O bond cleavage/Nazarov cyclization/nucleophilic addition reaction has been developed to afford a series of multisubstituted indenes with an all-carbon quaternary center in moderate to good yields.

Central-axial-central chirality transfer: asymmetric synthesis of highly substituted indenes bearing a stereogenic quaternary carbon center from optically active propargyl alcohols

An asymmetric synthesis of highly substituted indenes 3, bearing a quaternary stereogenic carbon center, has been developed via the central-axial-central chirality transfer from optically active propargyl alcohols 1. This transformation involves the addition/rearrangement of 1 and ynamides 2 to give tetra-substituted allenes 4 and further cyclization of 4.

Synthetic approaches to multifunctional indenes

The synthesis of multifunctional indenes with at least two different functional groups has not yet been extensively explored. Among the plausible synthetic routes to 3,5-disubstituted indenes bearing two different functional groups, such as the [3-(aminoethyl)inden-5-yl)]amines, a reasonable pathway involves the (5-nitro-3-indenyl)acetamides as key intermediates. Although several multistep synthetic approaches can be applied to obtain these advanced intermediates, we describe herein their preparation by an aldol-type reaction between 5-nitroindan-1-ones and the lithium salt of N,N-disubstituted acetamides, followed immediately by dehydration with acid. This classical condensation process, which is neither simple nor trivial despite its apparent directness, permits an efficient entry to a variety of indene-based molecular modules, which could be adapted to a range of functionalized indanones.

Zirconocene and Si-tethered diynes: a happy match directed toward organometallic chemistry and organic synthesis

Characterizing reactive organometallic intermediates is critical for understanding the mechanistic aspects of metal-mediated organic reactions. Moreover, the isolation of reactive organometallic intermediates can often result in the ability to design new synthetic methods. In this Account, we outline synthetic methods that we developed for a variety of diverse Zr/Si organo-bimetallic compounds and Si/N heteroatom-organic compounds through the detailed study of zirconacyclobutene-silacyclobutene fused compounds. Two basic components are involved in this chemistry. The first is the Si-tethered diyne, which owes its rich reactive palette to the combination of the Si-C bond and the C≡C triple bond. The second is the low-valent zirconocene species Cp(2)Zr(II), which has proven very useful in organic synthesis. The reaction of these two components affords the zirconacyclobutene-silacyclobutene fused compound, which is the key reactive Zr/Si organo-bimetallic intermediate discussed here. We discuss the three types of reactions that have been developed for the zirconacyclobutene-silacyclobutene fused intermediate. The reaction with nitriles (the C≡N triple bond) is introduced in the first section. In this one-pot reaction, up to four different components can be combined: the Si-tethered diyne can be reacted with three identical nitriles, with differing nitriles, or with a nitrile and other unsaturated organic substrates such as formamides, isocyanides, acid chlorides, aldehydes, carbodiimides, and azides. Several unexpected multiring, fused Zr/Si organo-bimetallic intermediates were isolated and characterized. A wide variety of N-heterocycles, such as 5-azaindole, pyrrole, and pyrroloazepine derivatives, were obtained. We then discuss the reaction with alkynes (the C≡C triple bond). A consecutive skeletal rearrangement, differing from that observed in the reactions with nitriles, takes place in this reaction. Finally, we discuss the reaction with the C═X substrates (where X is O or N), including ketones, aldehydes, and isocyanides. Oxa- and azazirconacycles are formed via a new skeletal rearrangement. Our results show that the zirconocene and the Si-tethered diyne cooperate as a "chemical transformer" after treatment with various substrates, leading to a diverse range of cyclic Zr/Si organo-bimetallic compounds. This mechanism-derived synthesis of organometallic and organic compounds demonstrates that the investigation of metal-mediated reactions and the isolation of reactive organometallic intermediates not only contribute to the understanding of complex reactions but can also lead to the discovery of synthetically useful methods.

Cleavage and reorganization of Zr-C/Si-C bonds leading to Zr/Si-N organometallic and heterocyclic compounds

The t-BuCN-stabilized zirconacyclopropene-azasilacyclopentadiene complexes 2 are generated in situ in high yields from the Si-tethered diynes, Cp(2)Zr(II) species, and 2 equiv of t-BuCN via a coordination-induced Zr-C/Si-C bond cleavage and reorganization. Complexes 2 have been demonstrated to be synthetically very useful. A variety of novel Zr/Si organo-bimetallic compounds and Si/N heterocyclic compounds, such as azasilacyclopentadienes, azasilacyclohexadienes, and allenylazazirconacycles, are obtained in high yields when complexes 2 are treated with ketones, carbodiimides, alkynes, elemental sulfur (S(8)), acid chlorides, or nitriles. In this chemistry, t-BuCN behaves as both an initiator and a brake/release handle to initiate and control the reaction process.