Coupling of enamides with alkynes or arynes for synthesis of substituted pyridines and isoquinolines via amide activation

A novel and general procedure for Cu-catalyzed coupling of enamides with alkynes to synthesize substituted pyridines was developed. The chemistry was allowed to extend to the synthesis of substituted isoquinolines by coupling of enamides with arynes under transition-metal-free conditions.     

Gold-catalyzed efficient tandem assembly of terminal alkynes and arynes: synthesis of alkynylated biphenyl derivatives

Gold catalysts have been found to catalyze the tandem assembly of arynes and terminal alkynes efficiently in the presence of CuI under mild reaction conditions to provide useful alkynylated biphenyl derivatives.     

DPTA-catalyzed one-pot regioselective synthesis of polysubstituted pyridines and 1,4-dihydropyridines

With diphenylammonium triflate (DPAT) as a catalyst, the highly substituted pyridines and dihydropyridines were prepared under solvent-free conditions from aldehydes, ketones, and amines via a one-pot multi-component reaction. The advantages of this protocol include excellent yields, environmentally benign source of nitrogen, mild reaction conditions, and simple manipulation. Different source of nitrogen like urea, thiourea, inorganic ammonium salts, and organic amines were studied. In addition, a novel way was developed for the conversion of primary aliphatic amines into alcohols.     

Copper-catalyzed three-component coupling of arynes, terminal alkynes and activated alkenes

The three-component coupling of benzynes with terminal alkynes and activated alkenes in the presence of CuI, PCy(3) and CsF in a 1:1 mixture of CH(3)CN and THF at 50 degrees C for 5 h gave 1-alkyl-2-alkynylbenzenes in good to moderate yields.     

Phosphine-catalyzed regioselective heteroaromatization between activated alkynes and isocyanides leading to pyrroles

The organophosphine catalyzed reaction of activated alkynes with isocyanides produces the corresponding heteroaromatization products, pyrroles, regioselectively in good yields. The reaction proceeds most probably through the 1,4-addition of the nucleophilic phosphine catalyst to the alkynes, followed by a [3+2] cycloaddition between the resulting alkenyl phosphine intermediates and a carbanion derived from the isocyanides.     

Rare-earth silylamide-catalyzed monocoupling reaction of isocyanides with terminal alkynes

[reaction: see text] Rare-earth silylamides, Ln[N(SiMe3)2]3 (Ln = Y, La, Sm, Yb), serve as good catalysts for monoinsertion of isocyanides into terminal alkynes in the presence of amine additives, leading to 1-aza-1,3-enyens in excellent yields. The reaction is applicable to a diverse set of terminal alkynes with various functionalities such as ethers, acetals, and amino groups. Larger metals (La and Sm) give a better performance than smaller ones (Y and Yb). Using less hindered primary amines and, in contrast, bulky isocyanides is crucial for the coupling reaction; otherwise, competitive oligomerization of the isocyanides occurs predominantly. In the mechanistic study, the rate-determining step of the reaction seems to be the first insertion of the isocyanides into rare-earth alkynides, which is followed by spontaneous protonation with the amine additives.     

Synthesis of pyridines from ketoximes and terminal alkynes via C-H bond functionalization

An expedient one-pot rhodium catalyzed C-H bond functionalization/electrocyclization/dehydration procedure has been developed for the synthesis of highly substituted pyridine derivatives from terminal alkynes and α,β-unsaturated ketoximes. The use of electron-deficient phosphite ligands is important to suppress dimerization of the terminal alkynes to enynes.     

Synthesis of isoquinolines and pyridines by the palladium-catalyzed iminoannulation of internal alkynes.

A wide variety of substituted isoquinoline, tetrahydroisoquinoline, 5,6-dihydrobenz[f]isoquinoline, pyrindine, and pyridine heterocycles have been prepared in good to excellent yields via annulation of internal acetylenes with the tert-butylimines of o-iodobenzaldehydes and 3-halo-2-alkenals in the presence of a palladium catalyst. The best results are obtained by employing 5 mol % of Pd(OAc)(2), an excess of the alkyne, 1 equiv of Na(2)CO(3) as a base, and 10 mol % of PPh(3) in DMF as the solvent. This annulation methodology is particularly effective for aryl- or alkenyl-substituted alkynes. When electron-rich imines are employed, this chemistry can be extended to alkyl-substituted alkynes. Trimethylsilyl-substituted alkynes also undergo this annulation process to afford monosubstituted heterocyclic products absent the silyl group.     

Iron catalyzed highly regioselective dimerization of terminal aryl alkynes

Iron can catalyze head-to-head dimerization of terminal aryl alkynes to give the corresponding (E) selective conjugated enynes in high yields. A variety of substituted aryl acetylenes underwent smooth dimerization using catalytic FeCl(3) and DMEDA in the presence of KO(t)Bu.     

Direct mono-insertion of isocyanides into terminal alkynes catalyzed by rare-earth silylamides

Rare-earth silylamide complexes, Ln[N(SiMe3)2]3 (Ln = Y, La, Sm, Yb), effectively catalyzed the coupling reaction of isocyanides with both aliphatic and aromatic terminal alkynes under mild conditions.     

Synthesis of isoquinolines and heterocycle-fused pyridines via three-component cascade reaction of aryl ketones, hydroxylamine, and alkynes

An efficient one-pot synthesis of isoquinolines and heterocycle-fused pyridines by three-component reaction of aryl ketones, hydroxylamine, and alkynes is developed. The reaction involves condensation of aryl ketones and hydroxylamine, rhodium(III)-catalyzed C-H bond activation of the in situ generated aryl ketone oximes, and cyclization with internal alkynes. This protocol enables rapid assembly of multisubstituted isoquinolines as well as γ-carbolines, furo[2,3-c]pyridines, thieno[2,3-c]pyridines, and benzofuro[2,3-c]pyridines from readily available substrates.     

Chemo- and regioselective cyclohydrocarbonylation of alpha-keto alkynes catalyzed by a zwitterionic rhodium complex and triphenyl phosphite

alpha-Keto alkynes react with CO and H(2) in the presence of catalytic quantities of the zwitterionic rhodium complex (eta(6)-C(6)H(5)BPh(3))(-)Rh(+)(1,5-COD) and triphenyl phosphite affording either the 2-, 2(3H)-, or 2(5H)-furanones in 61-93% yields. The cyclohydrocarbonylation is readily accomplished using substrates containing alkyl, aryl, vinyl, and alkoxy groups at the acetylenic terminal, as well as a variety of primary, secondary, and tertiary alkyl, aryl, and heteroaryl groups connected to the ketone functionality. Structural and electronic properties present in the starting materials mediate the chemo- and regioselectivity of the reaction.     

A catalytic synthesis of dihydrofuran-3(2H)-imine skeletons from isocyanides,terminal alkynes,and oxiranes

In this catalytic multicomponent reaction, the nucleophilicity of terminal alkynes and isocyanides towards oxiranes has been explored. The reaction outcome depends highly on solvent, bases, and catalysts sources. An array of terminal alkynes, isocyanides, and oxiranes has been examined to explore the of this transformation. The reactions proceeded through S_N2 path and in regioselective manner.     

Atom-economical chemoselective synthesis of 1,4-diynes and polysubstituted furans/pyrroles from propargyl alcohols and terminal alkynes

Under different conditions, the reaction of propargyl alcohols and terminal alkynes leads to the selective formation of 1,4-diynes and polysubstituted furans/pyrroles. Water is the only byproduct in the selective synthesis of 1,4-diynes and pyrroles, and the strategy for the furan synthesis is of 100% atom economy.     

Chemo- and regioselective intermolecular cyclotrimerization of terminal alkynes catalyzed by cationic rhodium(I)/modified BINAP complexes: application to one-step synthesis of paracyclophanes

A highly regioselective intermolecular cyclotrimerization of terminal alkynes has been developed based on the use of the cationic rhodium(I)/DTBM-Segphos complex. This method can be applied to a variety of terminal alkynes to provide 1,2,4-trisubstituted benzenes in high yield and with high regioselectivity. A chemo- and regioselective intermolecular crossed-cyclotrimerization of dialkyl acetylenedicarboxylates with a variety of terminal alkynes has also been developed based on the use of the cationic rhodium(I)/H8-BINAP complex, furnishing 3,6-disubstituted phthalates in high yields. It constitutes a highly efficient new method for intermolecular crossed-cyclotrimerization of two different monoynes in terms of catalytic activity, chemo- and regioselectivity, scope of substrates, and ease of operation. The versatility of this new crossed-alkyne cyclotrimerization procedure is demonstrated through its application to one-step synthesis of a [6]metacyclophane and [7]-[12]paracyclophanes from the corresponding terminal alpha,omega-diynes. Mechanistic studies have revealed that the chemo- and regioselectivity of this crossed-alkyne cyclotrimerization are determined by the preferential formation of a specific rhodium metallacycle derived from a terminal alkyne and a dialkyl acetylenedicarboxylate.     

Highly regioselective palladium/copper-catalysed cross-coupling reactions of terminal alkynes and allenes

The Pd/Cu-catalysed cross-coupling reaction of heterocyclic terminal alkynes and allene/allenyl heterocycles affords novel trisubstituted en-ynes in good yield.     

Nickel-catalyzed regioselective hydrocyanation of terminal alkynes by assistance of a tosyl group

Nickel-catalyzed regioselective hydrocyanation of terminal alkynes is described. A tosylamide functionality at the propargyl position was the most suitable group for controlling the regiochemistry for CCN bond formation as well as rate enhancement. A gram-scale synthesis was achieved by minimizing the catalyst loading to 2?mol%. The major HCN adduct could be transformed to the corresponding indoline through construction of a benzylic quaternary carbon under iron catalysis.     

Palladium-catalyzed three-component coupling of arynes with allylic acetates or halides and terminal alkynes promoted by cuprous iodide

Benzynes react with allylic acetates or halides and terminal alkynes in the presence of Pd(PPh3)4, CuI and CsF in CH3CN at 50 degrees C for 5 h to give 1-allyl-2-alkynylbenzene derivatives in good to excellent yields.     

Chemo- and regioselective reductive opening of azetidinium ions

Enantiomerically pure azetidinium trifluoromethanesulfonates were opened by various hydride reagents. LiAlH₄ and NaBH₃CN reacted with a complete regioselectivity and the latter reagent also reacted in a chemoselective way, leaving unaffected an ester or a cyano moiety present in the substrate. This reaction provides 1,2-diamines, 1,2- and 1,4-amino alcohols or α-amino esters by combining proper choice of substrate and hydride reagent.