Regio- and stereoselective synthesis of 1-aryl-1-thio-2-thiophosphinylethene derivatives via a radical process

Radical additions of S-thiophosphinyl dithiocarbonate to terminal aromatic alkynes afford (E)-1-aryl-1-thio-2-thiophosphinylethene derivatives regio- and stereoselectively in high yields. The transformations of the products are also described.     

Hydrothiolation of terminal alkynes with diaryl disulfides and diphenyl diselenide: selective synthesis of (Z)-1-alkenyl sulfides and selenides

A simple, stereoselective and efficient method for the hydrothiolation of terminal alkynes with diaryl disulfides and diphenyl diselenide has been developed. In the presence of CuI, rongalite, and Cs₂CO₃, a variety of disulfides underwent the reaction of terminal alkynes stereoselectively to afford the corresponding (Z)-1-alkenyl sulfides in moderate to excellent yields. It is noteworthy that hydroselenations of 1,2-diphenyldiselane with alkynes are also conducted smoothly to afford (Z)-1-alkenyl selenides in good yields under the standard conditions.     

Stable nitroxyl radicals with triple bonds: 4-acetylenyl-3-imidazoline-3-oxide-1-oxyls

Cross-coupling reaction of 1-hydroxy-2,2,5,5-tetramethyl-4-[2-(p-iodophenyl)vinyl]-3-imidazoline-3-oxide with copper(I) salts of 1-aryl(hetaryl)alkynes leads to the corresponding 2,2,5,5-tetramethyl-4-[2-(p-aryl(hetaryl)ethynylphenyl)vinyl]-3-imidazoline-3-oxide-1-oxyls in high yields.     

Rhodium-catalyzed carbothiolation reaction of 1-alkylthio-1-alkynes

A rhodium complex derived from RhH(PPh₃)₄ and Me₂PhP catalyzed the carbothiolation reaction of 1-alkylthio-1-alkynes and 1,4-diaryl-1,3-butadiynes giving (Z)-4-alkylthio-4-aryl-3-arylethynyl-3-buten-1-ynes. Terminal alkynes such as 1-decyne and (t-butylthio)acetylene underwent the carbothiolation reaction using a RhH(PPh₃)₄-dppb catalyst. The reactions proceeded via cis-addition with C-C bond formation at the less hindered acetylene carbon.     

Ni(II)-catalyzed C(sp2) H alkynylation/annulation cascades: Regioselective access to 3-methyleneisoindoline-1-one using N,S-bidentate auxiliary

A nickel(II)-catalyzed alkynylation/annulation of aryl carboxamides assisted by an N, S-bidentate directing group with terminal alkynes is described. This protocol provides an effective method to selectively furnish a series of biologically 3-methyleneisoindolin-1-one derivatives bearing methylthio group. Various carboxamides and terminal alkynes with a number of functional groups were compatible in this reaction to afford the corresponding products in moderate to good yields.     

Synthesis of (Z)-1-bromo-1-alkenes and terminal alkynes from anti-2,3-dibromoalkanoic acids by microwave-induced reaction

(Z)-1-Bromo-1-alkenes were stereoselectively prepared in high yields in a short reaction time by microwave irradiation of the corresponding anti-2,3-dibromoalkanoic acids in a Et₃N/DMF system. A one-pot synthesis of terminal alkynes and enynes from 2,3-dibromoalkanoic acids were also developed by microwave-induced reaction.     

Synthesis and equilibrium binding studies of cationic, two-coordinate gold(I) π-alkyne complexes

Reaction of a 1:1 mixture of (L)AuCl [L = P(t-Bu)₂o-biphenyl or IPr] and AgSbF₆ with internal alkynes led to isolation of the corresponding cationic, two-coordinate gold π-alkyne complexes in ≥ 90% yield. Equilibrium binding studies show that the binding affinities of alkynes to gold(I) are strongly affected by the electron density of the alkyne and to a lesser extent on the steric bulk of the alkyne. These substituent effects on alkyne binding affinity are greater than are the differences between the inherent binding affinities of alkynes and alkenes to gold(I).     

Synthesis and characterization of some ω-dimethylamino-1-alkynylzing compounds

Ethyl (ω-dimethylamino-1 -alkynyl)zinc compounds and bis (ω-dimethylamino-l-alkynyl)zinc compounds were prepared by metalation of the dimethyl amino alkynes HCC(CH₂)_n,NMe₂ (n = 1–4) with diethylzinc and diphenylzinc. All compounds show oligomeric or polymeric association in benzene, the degree of association being dependent on the value of n. The presence of coordinating dimethylamino groups and/or bridging alkynyl groups was established by IR and NMR spectroscopy. Plausible structures for all compounds, based on spectroscopic and molecular weight data, are presented.     

Hyperbaric laser chemical vapor deposition of carbon fibers from the 1-alkenes, 1-alkynes, and benzene

The growth of long carbon fibers was investigated using hyperbaric-pressure laser chemical vapor deposition (HP-LCVD). Precursors included the unbranched alkenes with linear structure 1-C(x)H(2x) (where x = 2,4,5,6,7,8), the unbranched alkynes, i.e., 1-C(x)H(2)(x-2) (where x = 3,4,5,6,8), and benzene. Rate constants, reaction orders, and apparent activation energies were derived for each precursor over a range of experimental conditions. Axial growth rates from the alkenes were 1-2 orders of magnitude greater than for the alkynes, while growth rates for benzene exceeded 10 mm s(-1). Generalized expressions for the growth rate vs molecular weight were determined. For the alkenes, the growth rate was directly proportional to the square root of the precursor molecular weight, while the alkynes exhibited an inverse relationship. Two regions of differing reaction order were identified for the alkynes; at pressures less than 2.0-2.5 bar, the average reaction order was 3.07, while above 2.0-2.5 bar, reaction orders diverged. Expressions were derived for the fraction of carbon atoms deposited per alkyne molecule transported; the deposition efficiency decreased with molecular weight for the alkynes, due in part to the Soret effect. In contrast, the reaction order for the alkenes was 1.65, and for benzene was 2.25. A phase change in the deposit was observed for both the alkenes and alkynes, with the exceptions of pentene and pentyne. Complete axial rate equations for the alkenes and alkynes were derived, as well as volumetric growth equations for the alkynes. It was shown that the volumetric rate increases nonlinearly with laser power at sufficiently high pressures.     

Palladium-catalyzed carbonylative annulation of terminal alkynes: synthesis of coumarins and 2-quinolones

o-Iodophenols and o-iodoaniline derivatives react with terminal alkynes under 1 atm of CO in the presence of pyridine and catalytic amounts of Pd(OAc)₂ to generate coumarins and 2-quinolones, respectively, as the only products. Terminal alkynes bearing alkyl, aryl, silyl, hydroxyl, ester and cyano substituents are effective in these processes affording the desired products in moderate yields. The formation of coumarins and 2-quinolones in this process is in stark contrast with all previously described palladium-catalyzed reactions of o-iodophenols or o-iodoanilines with terminal alkynes and CO, which have afforded chromones and 4-quinolones. Moreover, under our reaction conditions terminal alkynes insert into the carbonpalladium bond instead of undergoing a Sonogashira-type coupling as confirmed by an isotope labeling experiment.     

Photoactivated hydrosilylation reaction of alkynes

The photoactivated (350 nm) hydrosilylation of alkynes by silanes catalyzed by platinum(II) bis(acetylacetonato) has been studied. Platinum(II) bis(acetylacetonato) is an efficient catalyst. High yields of adducts (>98% for terminal alkynes) can be obtained in 2–3 h after a short induction period with a catalyst–reactant molar ratio of 10⁻³/1. The reaction rate depends on the choice of silane, irradiation time and the concentration of catalyst. The major product is the β-trans adduct. Minor products are the α isomer with a trace of β-cis isomer. Comparisons of hydrosilylation reactions of alkynes with hydrosilylation reactions of alkenes are reported.     

Facile synthesis of novel CF3-substituted ring-fused furo[2,3-c]pyrazoles through Rh2(OAc)4 catalyzed [3+2] cycloaddition of 4-diazo-1-phenyl-3-(trifluoromethyl)-1H-pyrazol-5(4H)-one with aromatic alkynes

The Rh₂(OAc)₄ catalyzed [3+2] cycloaddition of 4-diazo-1-phenyl-3-(trifluoromethyl)-1H-pyrazol-5(4H)-one with aromatic alkynes was studied, and this protocol can be efficiently applied to the synthesis of the novel CF₃-substituted ring-fused furo[2,3-c]pyrazoles.     

Sonogashira cross-coupling reactions of aryl chlorides with alkynes catalysed by a tetraphosphine-palladium catalyst

A range of aryl chlorides undergoes cross-couplings with alkynes in good yields in the presence of [PdCl(C₃H₅)]₂/cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane as catalyst. A variety of aryl chlorides such as chloroacetophenone, chlorobenzonitrile, chloronitrobenzene, chloroanisole or chlorotoluene have been used successfully. The reaction also tolerates several alkynes such as phenylacetylene, dec-1-yne, ethynylcyclohexene or alk-1-ynols. Furthermore, this catalyst can be used at low loading with some substrates.     

Retracted: A Facile Synthetic Route to New Fluorinated Building‐Blocks of 1‐Fluoroalkynes and 1‐Fluorodiynes

A facile and direct fluorination process of alkynes and diynes was developed. In the presence of n‐butyllithium, the reaction of a series of terminal alkynes and diynes with the electrophilic fluorinating reagent (NFSI) proceeded to afford various 1‐fluoroalkynes and 1‐fluoro‐1,3‐diynes in moderate to high yields.     

Synthesis of glyco-1-ynitols via 1,1-dibromo-1-alkenes from partially and unprotected aldoses

We report the synthesis of 1,1-dibromo-1-alkenes from partially and unprotected aldoses and the synthesis of glyco-1-ynitols from these dibromocompounds. The 1,1-dibromo-1-alkenes were obtained by the reaction of dibromomethyl-triphenylphosphonium bromide in the presence of zinc in refluxing 1,4-dioxane. As an example, when the reaction is performed on 2-deoxy-5-O-trityl-d-ribofuranose (1) the corresponding 1,1-dibromo-1-olefin, (2R,3S)-6,6-dibromo-1-O-trityl-hex-5-ene-1,2,3-triol (12), is obtained in 89% yield. These smooth reaction conditions led also to the achievement of the other olefins from other sugars with good yields (44-90%). The reaction of these olefins with n-butyllithium in THF at low temperature afforded the corresponding alkynes. So the reaction of (2R,3S)-6,6-dibromo-1-O-trityl-hex-5-ene-1,2,3-triol (12) with this alkyllithium reagent led to (2R,3S)-1-O-trityl-hex-5-yne-1,2,3-triol (23) in 87% yield. Other glyco-1-ynitols were obtained with satisfying yields (64-87%).     

Palladium-catalyzed [3+2+1] cyclocarbonylative coupling of 1,3-cyclohexanediones, alkynes, and carbon monoxide: an atom-economic route to chromene-2,5-dione derivatives

3,4,7,8-Tetrahydro-2H-chromene-2,5(6H)-dione derivatives were efficiently synthesized with excellent selectivity via a [3+2+1] cyclocarbonylative coupling of 1,3-cyclohexanediones, terminal alkynes, and CO catalyzed by Pd(PPh₃)₄.     

Metal free synthesis of quinoxalines from alkynes via a cascade process using TsNBr2

A metal free protocol for the synthesis of quinoxalines from alkynes has been developed. The reaction was carried out by treating alkynes with TsNBr₂ in presence of O-phenylenediamines in a mixture of acetonitrile and water (9:1). This one-pot reaction proceeds via an oxidative transformation of alkynes to α,α-dibromoketones in presence of TsNBr₂ and eventually to quinoxalines in presence of 1,2-diamines in a cascade process.     

Zr-Mediated hydroboration: stereoselective synthesis of vinyl boronic esters

An improved process for the preparation of (E)-vinylboronic esters via a Zr-mediated hydroboration of alkynes, especially oxygen-containing alkynes, is described.     

Regio- and stereoselective synthesis of (E)-1-bromo-2-iodoalkenes through iodobromination of internal alkynes

One-step synthesis of (E)-1-bromo-2-iodoalkenes from internal alkynes through IBr addition is described. The IBr was generated in situ from commercially available TMSBr and NIS. This simple protocol enables highly efficient regio- and stereoselective iodobromination of the triple bond on a gram scale in anti-mode, and provides a potentially diverse scaffold for preparation of differentially all-carbon tetrasubstituted olefins.     

A novel application of terminal alkynes as the homogeneous catalysts for acetalization and esterification

The theoretical study focused on the possible use of low-molecular-weight mono-as well as multifunctional terminal alkynes as catalysts for two reactions, which are known to be typically acid catalyzed - acetalization and esterification, is presented in this study. Multifunctional terminal alkynes [(diethynylbenzenes, triethynylbenzene, and tetrakis(4-ethynylphenyl)methane] were significantly more active than the monofunctional ones (cyclopropylacetylene, phenylacetylene, 3-cyclohexylprop-1-yne, 1-ethynyl-2-fluorobenzene, 1-ethynyl-4-fluorobenzene, 4-ethynyltoluene, 4-tert-butylphenylacetylene, and 2-ethynyl-α,α,α-trifluorotoluene), this fact can be partly explained by the higher amount of ethynyl groups per alkyne molecule. We confirmed that terminal ethynyl groups in low-molecular-weight alkynes can successfully act as acid catalytic centers for acetalization as well as for esterification.