Hg(OTf)2-catalyzed arylene cyclization

Novel Hg(OTf) 2-catalyzed arylene cyclization was achieved with highly efficient catalytic turnover (up to 200 times). The reaction takes place via protonation of allylic hydroxyl group by in situ formed TfOH of an organomercuric intermediate to generate a cationic species. Subsequent smooth demercuration regenerates the catalyst.     

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.     

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.     

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.     

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.     

Dimethyl sulfoxide-aided copper(0)-catalyzed intramolecular decarbonylative rearrangement of N-aryl isatins leading to acridones

Described here is the first example of Cu(0)-catalyzed intramolecular decarbonylative rearrangements of readily available N-aryl isatins assisted by solvent dimethyl sulfoxide(DMSO) under air atmosphere and additive-free conditions leading to various biologically important acridones in good to excellent yields.This novel transformation is proposed to go through a sequential DMSO-aided Cu insertion into the amide C-N bond,CO extrusion,Cu migration,reductive elimination and DMSO-aided proton migration processes,involving multiple types of bond cleavage and formation in a single chemical step.     

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.     

Bi(OTf)3 and SiO2-Bi(OTf)3 as effective catalysts for the Ferrier rearrangement

Bi(OTf)3 and SiO2-Bi(OTf)3 are found to effectively catalyze the Ferrier rearrangement of tri-O-acetyl glycals with different alcohols providing an effective route to 2,3-unsaturated O-glycosides with good anomeric selectivity and good to excellent yields after short reaction times.     

Rh(II)-catalyzed Sommelet-Hauser rearrangement

Catalytic Sommelet-Hauser rearrangement is reported. The Rh(II)-catalyzed reaction of aryldiazoacetates with ethyl benzylthioacetate affords Sommelet-Hauser rearrangement products in good to excellent yields. This reaction provides a reliable and efficient way to introduce a substituent to the ortho position of arylacetates.     

The first synthesis of 2-amino-1,4-dihydroquinolines

A versatile strategy is described for the synthesis of new 2-amino-1,4-dihydroquinolines. It involved a Knoevenagel condensation of N-protected-2-amino-5-bromobenzaldehyde with ethylcyanoacetate, followed by a cyclization and protection of the NH group to afford the key intermediates 7 or 19. Then various 1,4 addition reactions have been performed to introduce substituents on the upper part of the 2-amino-1,4-dihydroquinolines.     

Gold(I)-catalyzed propargyl Claisen rearrangement

Homoallenic alcohols are prepared from propargyl vinyl ethers using a trinuclear gold(I)-oxo complex, [(Ph3PAu)3O]BF4, as a catalyst for propargyl Claisen rearrangement at room temperature. The gold(I)-catalyzed reaction is effective for a diverse collection of propargyl vinyl ethers, including substrates containing aryl and alkyl groups at the propargylic position, and hydrogen, aryl, and alkyl substituents at the alkyne terminus. Tertiary propargyl vinyl ethers can be employed in the reaction, at slightly elevated temperatures, to afford tetrasubstituted allenes. Importantly, the rearrangement of 1,2-disubstituted vinyl ethers proceeds with excellent diastereoselectivity, and the rearrangement of chiral nonracemic propargyl vinyl ethers proceeds with excellent chirality transfer to furnish enantioenriched allenes.     

Palladium(II)-catalyzed isomerization-Claisen rearrangement of 2-alkoxy diallyl ethers

Diallyl ethers bearing an enol ether react in the presence of PdCl₂ as catalyst to give α-allyl α-alkoxy ketones by selective isomerization via formal 1,2-H migration at the more substituted allyl group, followed by Claisen rearrangement. This rearrangement is also promoted by AuCl₃ and IrCl₃, although the yields are lower with these catalysts.     

Synthesis of 2-cyclopentenones by gold(I)-catalyzed Rautenstrauch rearrangement

The rearrangement of 1-ethynyl-2-propenyl pivaloates to cyclopentenones catalyzed by cationic triphenylphosphinegold(I) complexes is described. The reaction tolerates both alkyl and aryl substitution at the acetylenic and olefinic positions. Importantly, the gold(I)-catalyzed rearrangement of enantioenriched propargyl pivaloates proceeds with excellent chirality transfer, thus providing a practical method for the enantioselective synthesis of cyclopentenones.     

o-Phthalic Anhydride/Zn(OTf)2 co-catalyzed Beckmann rearrangement under mild conditions

o-Phthalic anhydride/Zn(OTf)₂ co-catalyzed Beckmann rearrangement was developed, producing the corresponding amide in up to 99% yield with acid-sensitive functionalities tolerated well, and the scale of the reaction could be enlarged to 77 mmol and the excellent yield was maintained. A successive procedure was developed. Moreover, the reaction was carried out at rt under nearly neutral conditions, and the workup was concise. These features illustrated the potential of the protocol in amide synthesis.     

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.     

PtCl2-catalyzed rearrangement of methylenecyclopropanes

Alkylidenecyclopropanes readily convert into cyclobutene derivatives on treatment with catalytic amounts of PtCl2. The reaction is strongly accelerated when performed under an atmosphere of CO (1 atm). The resulting cyclobutenes are isolated in good to excellent yields for substrates bearing aliphatic as well as aromatic substituents R on their olefinic site. If the substituent R, however, is a very electron-rich arene, the cyclobutenes initially formed react further to give dimeric products with a previously unknown 1,2,2a,7a-tetrahydrospiro[cyclobuta[a]indene-7,1'-cyclobutane skeleton. A mechanism accounting for these experimental observations as well as for a deuterium-labeling experiment is proposed which implies reactive intermediates at the nonclassical cation/carbene interface. Furthermore it is shown that the PtCl2-catalyzed cyclobutene formation can be geared with subsequent ring-opening/ring-closing metathesis (ROM/RCM) events. Finally, a convenient "one pot" method for the preparation of the alkylidenecyclopropane substrates used in this study is presented, which is based on a modified Julia-Kocienski olefination of aldehydes with readily available 1-tert-butyl-1H-tetrazol-5-yl-cyclopropyl sulfone under Barbier conditions.     

A novel multicomponent reaction: easy access to ferrocenyl (alkylimino)-1,4-dihydroquinolines

A facile and rapid synthetic approach of ferrocenyl (alkylimino)-1,4-dihydroquinolines through a novel multicomponent reaction is described. This strategy is high yielding (60-90%). The easy removal of the ferrocenyl entity led to formation of substituted quinolines by microwave method.     

Gold(I)-catalyzed intramolecular rearrangement of vinylidenecyclopropanes

Vinylidenecyclopropanes 1 can undergo intramolecular rearrangement to give the corresponding functionalized 1,2-dihydronaphthalenes in the presence of gold catalyst under mild conditions. A plausible rearrangement mechanism has been proposed on the basis of control experiments.