Hg(OTf)2-catalyzed vinylogous semi-pinacol rearrangement leading to 1,4-dihydroquinolines

An efficient method for the construction of dihydroquinoline derivatives possessing a quaternary carbon center is developed by an application of Hg(OTf)(2)-catalyzed vinylogous semi-pinacol-type rearrangement. The reaction was found to be specifically catalyzed by mercury salt and to proceed via a bicyclic aminal.     

Hg(OTf)(2)-catalyzed direct vinylation of tryptamines and versatile applications for tandem reactions

We have developed a unique catalytic protocol for direct gem-vinylation of tryptamine derivatives employing Hg(OTf)(2) as the optimum catalyst. The intermolecular vinylations with a series of aromatic acetylenes proceeded under ambient temperature at the C2 positions of indoles with high functional group tolerance. Based on the mechanistic insights, we further developed the tandem reactions successfully constructing a quaternary center.     

Hg(OAc)(2).0.1Sc(OTf)(3)-catalyzed cycloisomerization of 2-(4-pentynyl)furan

[structure: see text]. Although the Hg(OTf)2.3TMU-catalyzed Friedel-Crafts-type reaction of 3-(4-pentynyl)furan afforded the exo cyclization product, the reaction of 2-(4-pentynyl)furan furnished a very low yield. We found a 10:1 mixed reagent of Hg(OAc)2 and Sc(OTf)3 showed remarkable catalytic activity for the latter transformation. The actual reacting species is presumed to be Hg(OAc)(OTf), which is efficiently generated in situ by mixing the two reagents.     

Virtually complete E-selective alpha,beta-unsaturated ester synthesis by Hg(OTf)2-catalyzed hydration of sec-ethoxyalkynyl acetate

The reaction of alkyl-substituted sec-ethoxyalkynyl acetates with water catalyzed by Hg(OTf)2 afforded alpha,beta-unsaturated esters in excellent yield with high catalytic turnover up to 1000 times under very mild reaction conditions with virtually complete E-selectivity, superior even to that of the HWE reaction.     

Hg(OTf)2-Catalyzed cyclization of alkynyl tert-butylcarbonate leading to cyclic enol carbonate

Mercuric triflate was shown to be a powerful catalyst for the cyclization of alkynyl tert-butylcarbonates giving rise to cyclic enol carbonates under mild conditions. Internal alkynyl carbonate affords endo cyclization product selectively, while terminal alkynyl carbonate provides only exo cyclization product.     

Bi(OTf)3-catalyzed cycloisomerization of aryl-allenes

Intramolecular hydroarylation of allenes was achieved under very mild conditions using bismuth(III) triflate as the catalyst. Efficient functionalization of activated and nonactivated aromatic nuclei led to C-C bond formation through a formal Ar-H activation. A tandem bis-hydroarylation of the allene moiety was also developed giving access to various interesting polycyclic structures.     

Nd(OTf)3-catalyzed intramolecular-intermolecular cascade cyclization reaction: An access to phenanthro[9,10-b]furan derivatives

An intramolecular-intermolecular cascade cyclization reaction via multi metal-carbene intermediates has been developed. This reaction uses catalytic amount of Nd(OTf)₃, which actives both alkyne and aldehyde moieties. This protocol provides a novel strategy for the synthesis of phenanthro[9,10-b]furans.     

Zn(OTf)2-catalyzed,microwave-promoted synthesis of 2-substituted 5-methyloxazoles from propargylic amides

The versatile conversion of propargylic amides to the respective 2-substituted 5-methyloxazoles was efficiently catalyzed by Zn(OTf)₂ (5?mol%) under microwave irradiation in toluene. The method was applicable to a wide range of aliphatic, aromatic and heteroaromatic propargylic amides and thus represents a useful method which is complementary to the existing metal-catalyzed protocols, considering the ready availability of Zn(OTf)₂.     

Efficient synthesis of isochromanones and isoquinolines via Yb(OTf)3-catalyzed tandem oxirane/aziridine ring opening/Friedel-Crafts cyclization

The first example of Yb(OTf)(3)-catalyzed tandem ring opening/Friedel-Crafts cyclization of oxiranyl and aziridinyl ketones via selective C-C bond cleavage under mild conditions was developed. Isochromanones and isoquinolines are formed in reasonable yields, which often serve as building blocks for complex chemical synthesis.     

Iron(III)-catalyzed Conia-ene cyclization of 2-alkynic 1,3-dicarbonyl compounds

A cheap, simple, and effective FeCl(3)-catalyzed Conia-ene cyclization of 2-alkynic 1,3-dicarbonyl compounds was stereospecific to afford alkylidenecyclopentanes in (E)-isomers via the 5-exo-dig pathway. The 5-endo-dig and 6-exo-dig cyclizations were also possible, depending on the structure of the substrates.     

Yb(OTf)3-catalyzed synthesis of pyrroles under solvent-tree conditions

Ayb(Otf)3-catalyzed approach for the synthesis of pyrroles under solvent-free conditions was achieved,which could afford the desired products with yields ranged from moderate to excellent.     

Palladium(0)-catalyzed cyclization of 2-butenylene dicarbamates forming 4-vinyl-2-oxazolidones

2-Butenylene dicarbamates prepared from but-2-en-1,4-diol and isocyanates readily undergo the cyclization in the presence of a phosphine-palladium(0) catalyst to produce 4-vinyl-2-oxazolidones in high yields.     

Ruthenium(II)-catalyzed cyclization of azabenzonorbornadienes with alkynes

The ruthenium-catalyzed cyclization of azabenzonorbornadienes with alkynes leads to an unanticipated dihydrobenzoindole framework. Depending on the structure of the alkyne and the Ru catalyst, either a dihydrobenzoindole and/or a [2+2] cycloaddition product could be formed. Cp*Ru(COD)Cl was found to be an active catalyst for the cyclization of an azabenzonorbornadiene with a propargylic alcohol to produce the dihydrobenz[g]indole as a single regio and stereoisomer in good yield. For other alkynes, selective formation of the dihydrobenz[g]indole is possible by using a cationic Ru catalyst, [Cp*Ru(CH3CN)3]PF6.     

Hg(OTf)2-Catalyzed cycloisomerization of 2-ethynylaniline derivatives leading to indoles

Cycloisomerization of 2-ethynylaniline derivatives catalyzed by mercuric triflate afforded indole derivatives in excellent yield under mild reaction conditions with high catalytic turnover up to 100 times.     

Ga(OTf)3-catalyzed direct substitution of alcohols with sulfur nucleophiles

It is reported that Ga(OTf)(3) catalyzes the direct displacement of alcohols with sulfur nucleophiles. The products are versatile intermediates that can be utilized in carbon-carbon, carbon-sulfur bond formation or used in modified Julia olefination reactions. The only byproduct generated is water.     

Yb（OTf）3-catalyzed synthesis of pyrroles under solvent-free conditions

A Yb(OTf)_3-catalyzed approach for the synthesis of pyrroles under solvent-free conditions was achieved,which could afford the desired products with yields ranged from moderate to excellent.     

Sc(OTf)3-catalyzed or t-BuOK promoted tandem reaction of 2-(2-(alkynyl)benzylidene)malonate with indole

Tandem reaction of 2-(2-(alkynyl)benzylidene)malonate with indole was investigated. (Z)-1-Benzylidene-3-(1 H-indol-1-yl)-1 H-indene-2,2(3 H)-dicarboxylate was generated in the presence of t-BuOK at room temperature; whereas 3-((1 H-indol-3-yl)(2-(alkynyl)aryl)methyl)-1 H-indole was obtained when Sc(OTf)3 was utilized as catalyst at 50 degrees C.     

Hg(OTf)2-catalyzed glycosylation using alkynoate as the leaving group

A novel Hg(OTf)₂-catalyzed glycosylation procedure has developed using alkynoic acid residues as the leaving group under mild reaction conditions and efficient catalytic turnover. The process is particularly useful for the glycosylation of hindered alcohols.