Novel and convenient synthesis of substituted quinolines by copper- or palladium-catalyzed cyclodehydration of 1-(2-aminoaryl)-2-yn-1-ols

A general and convenient synthesis of substituted quinolines by regioselective copper- or palladium-catalyzed 6-endo-dig cyclization-dehydration of 1-(2-aminoaryl)-2-yn-1-ols is reported. The crude substrates were easily obtained by the Grignard reaction between the appropriate alkynylmagnesium bromide and 2-aminoaryl ketones and could be used without further purification for the subsequent cyclization step. Heteroannulation reactions were carried out in MeOH or DME as the solvent at 60 or 100 degrees C in the presence of CuCl(2) or PdX(2) (in conjunction with 10 equiv of KX, X = Cl, I) as the catalyst to afford the quinoline derivatives in good to excellent isolated yields based on starting 1-(2-aminoaryl)-2-yn-1-ols (66-90%).     

Efficient synthesis of functionalized furans and benzofurans based on a ‘[3+2] cyclization/oxidation’ strategy

Functionalized furans and benzofurans were prepared by DDQ oxidation of 2-alkylidenetetrahydrofurans, which are readily available by one-pot cyclizations of 1,3-dicarbonyl dianions or 1,3-bis-silyl enol ethers.     

Formation of substituted 2-iminooxazolidines via intermolecular 1,2-addition/intramolecular N-vinylation using 3-substituted-2-bromo-2-propen-1-ols as substrates

The Cu₂O-catalyzed reaction between equimolar amounts of easily available 3-substituted-2-bromo-2-propen-1-ols and dicyclohexyl carbodiimide in DMSO at 100?°C using K₃PO₄ as the base and in the absence of any additive exclusively delivers substituted 2-iminooxazolidines with yields up to 80%. The highly selective transformation is assumed to start with an intermolecular 1,2-addition, which is followed by an intramolecular N-vinylation. The products can also be obtained in the absence of Cu₂O, albeit in lower yields.     

PtCl4-catalyzed cyclization of N-acetyl-2-alkynylanilines: A mild and efficient synthesis of N-acetyl-2-substituted indoles

An efficient synthesis of N-acetyl-2-substituted indole derivatives via direct intramolecular hydroamination of N-acetyl-2-alkynylaniline derivatives was developed. The reaction could be applied to a wide range of substrates employing only 1–2?mol% of PtCl₄ as the catalyst to furnish the desired indole products in moderate to excellent yields. The current protocol is efficient, reliable and scalable, and could serve as an important tool for convenient and rapid access to this important class of N-heterocyclic skeleton from readily available substrates.     

A mild and efficient AgSbF6-catalyzed synthesis of fully substituted pyrroles through a sequential propargylation/amination/cycloisomerization reaction

Development of an efficient synthesis of fully substituted pyrroles via a sequential propargylation/amination/cycloisomerization was accomplished using AgSbF₆ as a catalyst. The one-pot three-component reaction of propargylic alcohols, 1,3-dicarbonyl compounds, and primary amines proceeds at a mild temperature, which prevents the formation of furan by-product. The reaction was also successfully applied to the more basic aliphatic amines with the addition of 1.1 equiv of acetic acid.     

The efficient one-pot synthesis of tetraalkyl substituted furans from symmetrical acetylenes,EtAlCl2, and carboxylic esters catalyzed by Cp2TiCl2

A new one-pot method for the synthesis of tetraalkyl substituted furans in 74–80% yields has been implemented via the reaction between symmetrical acetylenes, ethylaluminum dichloride, and carboxylic esters in the presence of metallic Mg as an acceptor of halide ions, catalyzed by bis(cyclopentadienyl)titanium dichloride. A mechanism for the reaction is proposed and discussed.     

A general synthesis of diversely substituted indazoles and hetero-aromatic derivatives from o-halo-(het)arylaldehydes or -phenones

A set of variously substituted indazoles and hetero-aromatic derivatives were synthesized from o-halo-(het)arylaldehydes using a palladium catalyzed amination followed by cyclization. Starting from phenones, this process was extended to give 3-substituted indazoles. Moreover, N-1-substituted-indazoles can be reached by this strategy using an optional selective N-1-alkylation step during the process. This methodology offers a general and easy route for the synthesis of regioselectively substituted indazoles.     

Synthesis of functionalized pyrroles and 6,7-dihydro-1H-indol-4(5H)-ones by reaction of 1,3-dicarbonyl compounds with 2-azido-1,1-diethoxyethane

The condensation of 1,3-dicarbonyl compounds with 2-azido-1,1-diethoxyethane and subsequent cyclization allowed an efficient synthesis of a variety of pyrroles and 6,7-dihydro-1H-indol-4(5H)-ones.     

A general and efficient synthesis of substituted furans and dihydrofurans via gold-catalyzed cyclization of (Z)-2-en-4-yn-1-ols

A highly efficient Au-catalyzed cyclization of (Z)-enynols that proceeds under mild reaction conditions has been developed. This methodology provides rapid access to substituted furans and stereodefined (Z)-5-ylidene-2,5-dihydrofurans in a regioselective manner from suitably substituted (Z)-2-en-4-yn-1-ols.     

Electrophilic cyclization of 4-thio-but-2-yn-1-ols via 1,2-migration of the thio group: efficient synthesis of 2,4-dihalo-3-thio-substituted furans

A facile and efficient method for the synthesis of 2,4-dihalo-3-thio-furans via the electrophilic cyclization and 1,2-migration of the thio group of 4-thio-but-2-yn-1-ols was developed. As a result of the ready availability of starting materials and the simple and convenient operation, this synthetic route would have potential utility in organic synthesis.     

Cycloaddition of hydrazones and 1, 2-diarylalkynes promoted by t-BuOK/DMF: A convenient synthesis of tetraarylpyrazoles

A facile synthesis of tetraarylpyrazoles has been developed via t-BuOK/DMF promoted intermolecular cycloaddition of hydrazones and 1,2-diarylalkynes.     

Regioselective synthesis of benzo[c]chromen-6-ones by one-pot cyclocondensation of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with 4-chloro-2-oxo-2H-chromene-3-carbaldehyde

The cyclocondensation of 4-chloro-2-oxo-2H-chromene-3-carbaldehyde with 1,3-bis(silyloxy)-1,3-butadienes provides a convenient synthesis of benzo[c]chromen-6-ones.     

A simple and convenient synthesis of 2-(perfluoroalkyl)-4H-chromenes from salicyl N-tosylimines or salicylaldehydes and methyl 2-perfluoroalkynoates

Et₃N-catalyzed reactions of salicyl N-tosylimines or salicylaldehydes with methyl 2-perfluoroalkynoates proceed smoothly at room temperature in dichloromethane (DCM) or dimethyl sulfoxide (DMSO) to give the corresponding fluorinated chromenes in good to excellent yields with high regioselectivity.     

Pd(OAc)2-catalyzed domino reactions of 1,2-dihaloarenes and 2-haloaryl arenesulfonates with Grignard reagents: efficient synthesis of substituted fluorenes

Pd(OAc)₂-catalyzed domino reactions of 1,2-dihalobenzenes and 2-haloaryl arenesulfonates with hindered Grignard reagents to form substituted fluorenes, which are believed to occur through palladium associated aryne intermediates, are described. Such palladium associated aryne reaction pathway was found to be favored by omitting the use of phosphine and N-heterocyclic carbene ligands for palladium catalysts and with better leaving groups. Our study suggested that Pd(leaving group)X associated arynes should be formed first and the sp³ C-H activation preferentially occurred at benzylic C-(1°)H bonds. The work described here provides a high yield, one-step access to substituted fluorenes from readily available 1,2-dihalobenzenes and 2-haloaryl arenesulfonates and hindered Grignard reagents, and this substituted fluorene-making method may find applications in the preparation of substituted fluorene-containing molecules including polymers.     

A flexible synthesis of C-6 and N-1 analogues of a 4-amino-1,3-dihydroimidazo[4,5-c]pyridin-2-one core

A flexible route which enables access to derivatives of 4-amino-1,3-dihydroimidazo[4,5-c]pyridin-2-ones is described. Issues of selectivity, reaction safety, and low yields in original routes are overcome with the key improvements to the route, including a Negishi cross-coupling and use of a carbamate as a protecting group and intrinsic carbonyl source. The new route enables variation of C-6 and N-1 substituents.     

Facile and convenient synthesis of functionalized propargylic alcohols and amines: an InBr3-Et3N reagent system promotes the alkynylation of aldehydes and N,O- or N,S-acetals

The use of a novel InBr₃-Et₃N reagent system to promote the alkynylation of not only a variety of aromatic/heterocyclic or bulky aliphatic aldehydes but also N,O- or N,S-acetals is described. The use of N-silyl-N,O-acetals and 1-alkynes could lead to the direct production of primary propargylic amines in good yields.     

A simple and convenient synthesis of 4-methyl-3-nitro-2-trihalomethyl-2H-chromenes from N-unsubstituted imines of 2-hydroxyacetophenones and trichloro(trifluoro)ethylidene nitromethanes

The reaction of N-unsubstituted imines of 2-hydroxyacetophenones with trichloro(trifluoro)ethylidene nitromethanes in the presence of DABCO proceeds via tandem oxa-Michael/aza-Henry additions (in dichloromethane) or aza-Michael addition (in benzene) to give 4-methyl-3-nitro-2-trichloro(trifluoro)methyl-2H-chromenes or 1,1,1-trichloro(trifluoro)-3-nitro-N-[1-(2-hydroxyaryl)ethylidene]propan-2-amines, respectively.