Titanocene-catalyzed regioselective carbomagnesation of alkenes and dienes

A new method for regioselective carbomagnesation of alkenes and dienes has been developed by the use of a titanocene catalyst. This reaction proceeds efficiently at 0 degrees C in THF in the presence of Cp(2)TiCl(2) by the combined use of organic halides (R-X; R = alkyl, aryl and vinyl) and n-BuMgCl to afford benzyl, alpha-silylalkyl, or allyl Grignard reagents, which were trapped with various electrophiles. The present reaction involves (i) addition of carbon radicals toward alkenes or dienes in the carbon-carbon bond-forming step and (ii) transmetalation on Ti of benzyl-, alpha-silylalkyl-, or allyltitanocene with n-BuMgCl in the carbon-magnesium bond-forming step. The scope and limitations of this reaction have also been examined.     

Microwave-assisted palladium-catalyzed regioselective cyanothiolation of alkynes with thiocyanates

Applying microwave irradiation to palladium-catalyzed cyanothiolation of alkynes dramatically shortened the reaction time with good to excellent isolated yields.     

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.     

Stereo- and regioselective gold-catalyzed hydroamination of internal alkynes with dialkylamines

We report the use of a P,N-ligand to support a gold complex as a state-of-the-art precatalyst for the stereoselective hydroamination of internal aryl alkynes with dialkylamines to afford E-enamine products. Substrates featuring a diverse range of functional groups on both the amine (ether, sulfide, N-Boc amine, fluoro, nitrile, nitro, alcohol, N-heterocycles, amide, ester, and carboxylic acid) and alkyne (ether, N-heterocycles, N-phthalimide amines, and silyl ethers) are accommodated with synthetically useful regioselectivity.     

Remote ether groups-directed regioselective and chemoselective cycloaddition of azides and alkynes

Remote ether groups could be used as directing groups to prepare fully substituted 5-ether-1,2,3-triazoles with exclusive 1,5-regioselectivities and excellent chemoselectivities. Ether group could coordinate with iridium catalyst by lone-pair electron at a distance (up to four σ bonds) away from alkyne to control the regioselectivity by weak coordination effect. The cycloaddition reaction chemoselectively occurred at the propargyl ether moiety of diyne to give unique fully substituted 4-alkynyl-triazole.     

Silver-catalyzed regioselective carbomagnesiation of alkynes with alkyl halides and Grignard reagents

A silver-catalyzed carbomagnesiation of alkynes with alkyl halides and Grignard reagents afforded alkenyl Grignard reagents regioselectively, where the alkyl group of the alkyl halide, but not that of the Grignard reagent, was introduced into the alkyne. Application to δ-haloalkylacetylenes yielded cyclopentanes or a tetrahydrofuran containing an exo-methylene substituent via 5-exo-dig cyclization.     

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.     

A highly regioselective palladium-catalyzed hydrophosphination of alkynes using a diphosphine-hydrosilane binary system

A novel transition-metal-catalyzed hydrophosphination of terminal alkynes using a diphosphine-hydrosilane binary system takes place regioselectively to provide vinylic phosphines, which undergo air oxidation during workup, affording the corresponding vinylphosphine oxides in good yields. In this hydrophosphination, hydrosilanes act as a useful hydrogen source, and furthermore, small amounts of oxygen is required to accomplish the reaction efficiently.     

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.     

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.     

A simple cobalt catalyst system for the efficient and regioselective cyclotrimerisation of alkynes

The intermolecular cyclotrimerisation of terminal and internal alkynes can be catalysed by simple cobalt complexes such as a CoBr2(diimine) under mild reaction conditions when treated with zinc and zinc iodide with high regioselectivity in excellent yields.     

Hydroarylation of alkynes and alkenes through alumina-sulfuric acid catalyzed regioselective CC bond formation

A highly atom-efficient synthetic protocol for hydroarylation of terminal-aryl alkynes and styrene through the regioselective CC bond formation via the electrophilic addition of naphthols and substituted phenols has been developed using alumina-sulfuric acid as a heterogeneous supported solid acid catalyst. This methodology shows excellent regioselectivity and affords the desired product in good to excellent yield. The heterogeneous catalyst can also be recycled efficiently without much loss of activity.     

Stereoretentive and regioselective selenium-catalyzed intermolecular propargylic C–H amination of alkynes

Herein we report an intermolecular propargylic C–H amination of alkynes. This reaction is operationally convenient and requires no transition metal catalysts or additives. Terminal, silyl, and internal alkynes bearing a wide range of functional groups can be aminated in high yields. The regioselectivity of amination for unsymmetrical internal alkynes is strongly influenced by substitution pattern (tertiary > secondary > primary) and by relatively remote heteroatomic substituents. We demonstrate that amination of alkynes bearing α-stereocenters occurs with retention of configuration at the newly-formed C–N bond. Competition experiments between alkynes, kinetic isotope effects, and DFT calculations are performed to confirm the mechanistic hypothesis that initial ene reaction of a selenium bis(imide) species is the rate- and product-determining step. This ene reaction has a transition state that results in substantial partial positive charge development at the carbon atom closer to the amination position. Inductive and/or hyperconjugative stabilization or destabilization of this positive charge explains the observed regioselectivities.

Selenium catalysis enables a general intermolecular propargylic C–H amination of alkynes. The concerted mechanism gives rise to high regioselectivity for the more electron-rich end of the alkyne and retention of the C–H propargylic stereocenter.     

A highly regioselective Cu-exchanged tungstophosphoric acid catalyst for hydroarylation and hydroamination of alkynes

An efficient and reusable Cu-exchanged tungstophosphoric acid catalyst is demonstrated for the solvent free hydroarylation and hydroamination reactions of alkynes with numerous arene and amine derivatives, respectively. The catalyst exhibited exceptionally high activity and regioselectivity in both the reactions.     

Copper catalyzed regioselective coupling of allylic halides and alkynes promoted by weak inorganic bases

Allylic halides and terminal alkynes couple under CuI catalysis in DMSO or DMF solution. In most cases, sodium carbonate or bicarbonate is sufficient to promote the reaction; less reactive alkynes require catalytic amounts of DBU. Bifunctional alkynes and halides can be reacted selectively according to the stoichiometry used. Trimethylsilyl, hydroxyl, ester and halide groups are tolerated in the alkyne. Most halides react without allylic rearrangement. The method is suitable for the synthesis of functionalized enynes.     

Totally chemo- and regioselective cobalt(I)-mediated formal intermolecular cyclotrimerization of alkynes

[reaction: see text] The first examples of totally chemo- and regioselective formal intermolecular cobalt(I)-catalyzed [2 + 2 + 2] cyclizations of three different alkynes are reported. The use of disposable silylated tethers in the sequence cyclization followed by the displacement of the silicon group led to polysubstituted arenes as a unique cycloadduct in high yields.     

Nickel-mediated regioselective [2 + 2 + 2] cycloaddition of carboryne with alkynes

Transition metal-benzyne complexes have found many applications in organic synthesis, mechanistic studies, and the synthesis of functional materials. In sharp contrast, the chemistry of transition metal-carboryne complexes, especially late transition metal complexes, is virtually unknown. This communication reports a novel nickel-mediated regioselective [2 + 2 + 2] cycloaddition reaction of carboryne with alkynes via the Ni-carboryne intermediate (eta2-C2B10H10)Ni(PPh3)2. Because of the bulkiness of the carborane moiety, a high regioselectivity was achieved in the reactions involving unsymmetrical alkynes. This work furnishes a novel method for the preparation of highly substituted benzocarboranes which are difficult to obtain by other methods.     

Highly dispersed nano-copper catalyst on porous polyvinyl chloride for highly regioselective borylation of alkynes

We developed a highly regioselective synthesis of multi-substituted alkenylboronates via a heterogeneous ligand-free nano-copper catalyst that was highly dispersed and supported on the porous polyvinyl chloride. In this catalytic system, substituents on the terminal alkynes could affect the configuration of products. Terminal alkynes and general internal alkynes gave β-selective borylation products, whereas heteroatom-substituted alkynes like alkynamides, thioacetylenes, and ynol ethers gave α-selective borylation products in good chemical yields with exclusive regioselectivity.