Internal Alkynes Research Articles

Photoinitiated by Red Light (λ 625 nm) Iodosulfonylation of Internal Alkynes to Synthesize β-Iodovinyl Sulfones

A number of β-iodovinyl sulfones were synthesized by direct difunctionalization of internal alkynes with arenesulfonyl iodides under irradiation with red light (λmax 625 nm) generated by an economical LED source. The products were obtained in high yields (68–99%) from equimolar amounts of the reactants. The reaction of sulfonyl iodides with internal alkynes follows a radical mechanism and provides a regioselective method of synthesis of β-iodovinyl sulfones.

Methods for the Synthesis of 1-Indanones Containing a β-Quaternary Carbon Center

AbstractThis article traces the development of synthetic routes toward 1-indanones containing a β-quaternary carbon center. The recent advancement in the regio- and chemoselective formal (4+1) carbocyclization of chalcones with internal alkynes via rhodium(III) catalysis for the synthesis of 1-indanones is highlighted.

Photocatalytic Thiol-Yne Reactions of Alkynyl Sulfides.

Thiol-yne reactions typically employ thiols and terminal alkynes as the reaction partners. The thiol-yne reaction of alkynyl sulfides and thiols is possible when employing a nonmetal photocatalyst eosin Y, green LED irradiation, under an air atmosphere. Alkynyl sulfides were transformed in good overall yields (58-90% total yields, 11 examples) favoring the cis isomer. No addition to the α-position of the alkynyl sulfide is observed, and regioselectivity is believed to be controlled through the stabilization of radical intermediates by the adjacent sulfur atom. Furthermore, control experiments with "all-carbon" internal alkynes demonstrate that alkynyl sulfides possess improved reactivity and regioselectivity profiles during thiol-yne processes.

Experimental and Computational Studies on Uranium Diazomethanediide Complexes.

Uranium diazomethanediide complexes can be prepared and their synthesis, structure and reactivity were explored. Reaction of the uranium imido compound [η5 -1,2,4-(Me3 Si)3 C5 H2 ]2 U=N(p-tolyl)(dmap) (1) or [η5 -1,3-(Me3 C)2 C5 H3 ]2 U=N(p-tolyl)(dmap) (4) with Me3 SiCHN2 cleanly yields the first isocyanoimido metal complexes [η5 -1,2,4-(Me3 Si)3 C5 H2 ]2 U(=NNC)(μ-CNN=)U(dmap)[η5 -1,2,4-(Me3 Si)3 C5 H2 ]2 (2) and {[η5 -1,3-(Me3 C)2 C5 H3 ]2 U[μ-(=NNC)]}6 (5), respectively. Both compounds exhibit remarkable thermal stability and were fully characterized. According to density functional theory (DFT) studies the bonding between the Cp2 U2+ and [NNC]2- moieties is strongly polarized with a significant 5 f orbital contribution, which is also reflected in the reactivity of these complexes. For example, complex 5 acts as a nucleophile toward alkylsilyl halides and engages in a [2+2] cycloaddition with CS2 , but no reaction occurs in the presence of internal alkynes.

Experimental and Computational Studies on Uranium Diazomethanediide Complexes

AbstractUranium diazomethanediide complexes can be prepared and their synthesis, structure and reactivity were explored. Reaction of the uranium imido compound [η5‐1,2,4‐(Me3Si)3C5H2]2U=N(p‐tolyl)(dmap) (1) or [η5‐1,3‐(Me3C)2C5H3]2U=N(p‐tolyl)(dmap) (4) with Me3SiCHN2 cleanly yields the first isocyanoimido metal complexes [η5‐1,2,4‐(Me3Si)3C5H2]2U(=NNC)(μ‐CNN=)U(dmap)[η5‐1,2,4‐(Me3Si)3C5H2]2 (2) and {[η5‐1,3‐(Me3C)2C5H3]2U[μ‐(=NNC)]}6 (5), respectively. Both compounds exhibit remarkable thermal stability and were fully characterized. According to density functional theory (DFT) studies the bonding between the Cp2U2+ and [NNC]2− moieties is strongly polarized with a significant 5 f orbital contribution, which is also reflected in the reactivity of these complexes. For example, complex 5 acts as a nucleophile toward alkylsilyl halides and engages in a [2+2] cycloaddition with CS2, but no reaction occurs in the presence of internal alkynes.

Iterative Dual-Metal and Energy Transfer Catalysis Enables Stereodivergence in Alkyne Difunctionalization: Carboboration as Case Study.

Stereochemically defined tetrasubstituted olefins are widespread structural elements of organic molecules and key intermediates in organic synthesis. However, flexible methods enabling stereodivergent access to E and Z isomers of fully substituted alkenes from a common precursor represent a significant challenge and are actively sought after in catalysis, especially those amenable to complex multifunctional molecules. Herein, we demonstrate that iterative dual-metal and energy transfer catalysis constitutes a unique platform for achieving stereodivergence in the difunctionalization of internal alkynes. The utility of this approach is showcased by the stereodivergent synthesis of both stereoisomers of tetrasubstituted β-boryl acrylates from internal alkynoates with excellent stereocontrol via sequential carboboration and photoisomerization. The reluctance of electron-deficient internal alkynes to undergo catalytic carboboration has been overcome through cooperative Cu/Pd-catalysis, whereas an Ir complex was identified as a versatile sensitizer that is able to photoisomerize the resulting sterically crowded alkenes. Mechanistic studies by means of quantum-chemical calculations, quenching experiments, and transient absorption spectroscopy have been applied to unveil the mechanism of both steps.

Regioselective [3 + 2] cycloaddition of diazo reagents and internal alkynes: Accessing regiosomers of highly substituted trifluoromethylpyrazoles

We herein descript a metal-free and highly regioselective [3 + 2] cycloaddition reaction between diazo compounds and internal alkynes, accessing to a series of trifluoromethylated pyrazoles. Using different combination of starting materails, both regioisomers can be obtained under this protocal. The developed cycloaddition reaction provides a valuable tool for future medicinal chemistry research on highly substituted trifluoromethyl pyrazoles.

Diastereoselective Pd-catalyzed Decarboxylative (4 + 2) Cycloaddition Reactions of 4-Vinylbenzoxazinanones and 2-Nitro-1,3-enynes.

A formal palladium-catalyzed decarboxylative (4 + 2) cycloaddition reaction between 4-vinylbenzoxazinanones and 2-nitro-1,3-enynes has been developed to produce highly valuable, densely functionalized tetrahydroquinolines in moderate to excellent yields with high diastereoselectivity under mild reaction conditions. The optimised protocol tolerates a range of substituted 2-nitro-1,3-enynes, which represent an under-utilized class of dipolarophile for transition-metal catalyzed cycloadditions. The employed reaction methodology facilitates efficient cycloaddition with both N-H- and N-Ts-4-vinylbenzoxazinanone dipole precursors. The stereochemistry of the major and minor diastereomeric (4 + 2) cycloadducts was determined by single crystal X-ray analyses. A mechanistic rationale for the high intrinsic diastereoselectivity and preliminary enantioselective experiments are also presented. The tetrahydroquinoline cycloadduct products feature numerous pendant functionalities, including a vinyl handle, an internal alkyne motif and a nitro functionality (which functions as a latent C-3 nitrogen substituent) for further synthetic manipulations.

Copper-Catalyzed Regio- and Stereoselective Formal Hydro(borylmethylsilyl)ation of Internal Alkynes via Alkenyl-to-Alkyl 1,4-Copper Migration.

Catalytic reactions involving 1,n-metal migration from carbon to carbon enable a nonclassical way of constructing organic molecular skeletons, rapidly providing complex molecules from relatively simple precursors. By utilization of this attractive feature, a new and efficient synthesis of alkenylsilylmethylboronates has been developed by formal hydro(borylmethylsilyl)ation of unsymmetric internal alkynes with silylboronates under copper catalysis. The reaction proceeds regioselectively and involves an unprecedented alkenyl-to-alkyl 1,4-copper migration. The reaction mechanism has been investigated by a series of kinetic, NMR, and deuterium-labeling experiments.

Tunable Supramolecular Ag+-Host Interactions in Pillar[n]arene[m]quinones and Ensuing Specific Binding to 1-Alkynes.

We developed an improved, robust synthesis of a series of pillar[6]arenes with a varying number (0-3) of quinone moieties in the ring. This easy-to-control variation yielded a gradually less electron-rich cavity in going from zero to three quinone units, as shown from the strength of host-guest interactions with silver ions. Such macrocycle-Ag2 complexes themselves were shown to display an unprecedented, sharp distinction between terminal alkynes, which strongly bound to such complexes, and internal alkynes, internal alkenes and terminal alkenes, which do hardly bind.

Regioselective electrochemical radical cascade cyclization of internal alkynes to selenated and trifluoromethylated dihydropyran

Regioselective electrochemical radical cascade cyclization of internal alkynes to selenated and trifluoromethylated dihydropyran

Atroposelective Synthesis of C-N Vinylindole Atropisomers by Palladium-Catalyzed Asymmetric Hydroarylation of 1-Alkynylindoles.

Transition-metal-catalyzed hydroarylation of unsymmetrical internal alkynes remains challenging because of the difficulty in controlling regioselectivity and stereoselectivity. Moreover, the enantioselective hydroarylation of alkynes using organoboron reagents has not been reported. Herein, we report for the first time that palladium compounds can catalyze the hydroarylation of 1-alkynylindoles with organoborons for the synthesis of chiral C-N atropisomers. A series of rarely reported vinylindole atropisomers was synthesized with excellent regio-, stereo- (Z-selectivity), and enantioselectivity under mild reaction conditions. The ready availability of organoborons and alkynes and the simplicity, high stereoselectivity, and good functional group tolerance of this catalytic system make it highly attractive.

Atroposelective Synthesis of C−N Vinylindole Atropisomers by Palladium‐Catalyzed Asymmetric Hydroarylation of 1‐Alkynylindoles

AbstractTransition‐metal‐catalyzed hydroarylation of unsymmetrical internal alkynes remains challenging because of the difficulty in controlling regioselectivity and stereoselectivity. Moreover, the enantioselective hydroarylation of alkynes using organoboron reagents has not been reported. Herein, we report for the first time that palladium compounds can catalyze the hydroarylation of 1‐alkynylindoles with organoborons for the synthesis of chiral C−N atropisomers. A series of rarely reported vinylindole atropisomers was synthesized with excellent regio‐, stereo‐ (Z‐selectivity), and enantioselectivity under mild reaction conditions. The ready availability of organoborons and alkynes and the simplicity, high stereoselectivity, and good functional group tolerance of this catalytic system make it highly attractive.

Preparation of Multifunctional Regio‐ and Stereo‐Regular hb‐Polyamines via C(sp3)─H Activation‐Based Polyamination of Internal Alkynes

AbstractHyperbranched polymers have been widely applied in various fields because of their good solubility, high reactive end groups, and low viscosity, etc. Therefore, it is of great importance to develop new strategies to build multifunctional hyperbranched polymers with novel architectures. In this work, a C(sp3)─H activation‐based polymerization of internal alkynes and bifunctional secondary amines is successfully established, and multifunctional hyperbranched polyamines (hb‐PAs) with 100% E‐isomers and high molecular weights (Mw up to 76 500) are prepared in good yields (up to 82%). The hb‐PAs containing tetraphenylethylene moiety show unique aggregation‐enhanced emission properties and can be used for explosive detection with a low limit of detection (9.14 × 10−8 m). Notably, the hb‐PAs display high refractive indices (up to 1.7607) that can be further modulated to 1.7825 by the coordination of its peripheral ethynyl group with metallic cobalt. Moreover, the hyperbranched structure endows the hb‐PAs with much better properties than their linear counterparts, such as higher photoluminescence quantum yields and refractive indices. In addition, the hb‐PAs can be modified by a C(sp3)─H activation reaction of internal alkynes and alcohols. This work not only prepares a series of functional nitrogen‐containing hyperbranched polymers but also promotes the application of C(sp3)─H activation in polymer chemistry.

Iron‐Catalyzed Alkenylzincation of Internal Alkynes†

Comprehensive SummaryThe alkenylzincation of internal alkynes is an effective method for the synthesis of multi‐substituted conjugated dienes; however, the current catalytic systems for this reaction are limited in terms of substrate scope and selectivity control, which restricts its practical applications. Herein, we report the first iron‐catalyzed alkenylzincation of internal alkynes, which features mild conditions, simple operation, broad substrate scope (including aryl/alkyl, diaryl, and dialkyl acetylenes), excellent functional group tolerance (tolerating highly active functional groups such as ester, methylthio, amide, sulfonyl, cyano, etc.), and high activity (with a turnover number of up to 11500, the highest record for carbometallation reactions). Notably, the catalytic system described in this article also realized the highly selective vinylzincation of unfunctionalized internal alkynes as well as the alkenylzincation of unsymmetrical diarylacetylenes and dialkyl acetylenes, which have not been achieved with other catalytic systems reported in the literatures. The current study provides a highly selective access to synthetically important multi‐substituted conjugated dienes.

Photoinduced NiH Catalysis with Trialkylamines for the Stereodivergent Transfer Semi-Hydrogenation of Alkynes.

We report a selectivity-switchable nickel hydride-catalyzed methodology that enables the stereocontrolled semi-reduction of internal alkynes to E- or Z-alkenes under very mild conditions. The proposed transfer semi-hydrogenation process involves the use of a dual nickel/photoredox catalytic system and triethylamine, not only as a sacrificial reductant, but also as a source of hydrogen atoms. Mechanistic studies revealed a pathway involving photo-induced generation of nickel hydride, syn-hydronickelation of alkyne, and alkenylnickel isomerization as key steps. Remarkably, mechanistic experiments indicate that the control of the stereoselectivity is not ensuing from a post-reduction alkene photoisomerization under our conditions. Instead, we demonstrate that the stereoselectivity of the reaction is dependent on the rate of a final protonolysis step which can be tuned by adjusting the pKa of an alcohol additive.

Isostructural Series of Ni(II), Pd(II), Pt(II), and Au(III) Azido Complexes with a N^C^N Pincer Ligand to Elucidate Trends in the iClick Reaction Kinetics and Structural Parameters of the Triazolato Products.

An isoelectronic and isostructural series of cyclometalated azido complexes [M(N3)(dpb)] with M = Ni(II), Pd(II), Pt(II), and Au(III) based on the N^C^N pincer ligand 1,3-di(2-pyridyl)phenide (dpb) was characterized by X-ray diffraction analysis and investigated for reactivity in the iClick reaction with a wide range of internal and terminal alkynes by using 1H and 19F NMR spectroscopy. Reaction rate constants were found to increase with greater charge density in the order Ni(II) > Pd(II) > Pt(II) > Au(III). Terminal alkynes R-C≡C-R' with strongly electron-withdrawing groups R and R' exhibited faster kinetics than those with electron-donating substituents in the order CF3 > ketone > ester > H > phenyl ≫ amide, while R = CH3 resulted in complete loss of reactivity. Four symmetrical triazolato complexes [M(triazolatoCOOCH3,COOCH3)(dpb)] with M = Ni(II), Pd(II), Pt(II), and Au(III) as well as four nonsymmetrically substituted triazolato complexes [Pt(triazolatoR,R')(dpb)] originating from terminal and internal alkynes were shown by X-ray crystal structure analysis to exclusively feature N2-coordination of the five-membered ring ligand. However, the Pt(II) triazolato complexes exist as a mixture of N1- and N2-coordinated species in solution. Torsion angles between the mean planes of the N^C^N pincer and the triazolato ligand increase from a nearly coplanar to a perpendicular arrangement when going from Au(III)/Pt(II)/Pd(II) to Ni(II), while different substituents R and R' on the alkyne have no influence on the torsion angle and were rationalized by DFT calculations. Finally, a carbohydrate derivative obtained by glucuronic acid conjugation to methyl propiolate demonstrates the facile biofunctionalization of metal complexes via the iClick reaction.

Gold-Zinc Cooperative Catalysis for Seven-exo-dig Hydrocarboxylation of Internal Alkynes.

Seven-exo-dig hydrocarboxylation of nonactivated internal alkynes with conformationally flexible linker chains was achieved with cooperative gold-zinc catalysts composed of an imidazo[1,5-a]pyridinylidene ligand including a bipyridine coordination site at the C5 position. A proximity effect of the gold and zinc sites was essential for their high catalytic activity, in which the internal alkyne activated by the cationic gold species was attacked by the carboxylic acid deprotonated by the basic zinc site. Using a gold(I)-complex with a bulky aromatic N-substituent, 2,6-dibenzhydryl-4-methylphenyl group, for the NHC ligand facilitated seven-membered ring formation while minimizing intermolecular hydrocarboxylation as an undesired side reaction. The reaction mechanism was investigated by quantum chemical calculations.

Organocatalytic [3+2] Cycloaddition Reaction: Synthesis of Fully Decorated Sulfonyl 1,2,3‐Triazoles as Potent EGFR Targeting Anticancer Agents**

AbstractA general strategy was developed for the synthesis of new fully decorated sulfonyl1,2,3‐triazolyl imidazoles from β‐ketosulfones and several aryl sulfonyl azides using the ramachary organocatalytic cycloaddition method. Organocatalytic [3+2] cycloaddition reaction of β‐ketosulfone acts as an internal alkyne, as reported for the synthesis of sulfonyl‐1,2,3‐triazolyl imidazoles at 80 °C in good to excellent yields of products in the presence of catalytic amounts of pyrrolidine (10 mol %). In vitro anticancer activity of all these derivatives revealed that four compounds like 4‐((5‐(4‐methoxyphenyl)‐4‐((1‐methyl‐1H‐imidazol‐2‐yl) sulfonyl)‐1H‐1,2,3‐triazol‐1‐yl)sulfonyl) benzonitrile, 5‐(4‐methoxyphenyl)‐4‐((1‐methyl‐1H‐imidazol‐2‐yl)sulfonyl)‐1‐((4‐nitro phenyl) sulfonyl)‐1H‐1,2,3‐triazole,4‐((4‐((1‐methyl‐1H‐imidazol‐2‐yl) sulfonyl)‐5‐(4‐nitrophenyl)‐1H‐1,2,3‐triazol‐1‐yl)sulfonyl)benzonitrile, and 1‐((4‐chlorophenyl)sulfonyl)‐4‐((1‐methyl‐1H‐imidazol‐2‐yl) sulfonyl)‐5‐(4‐nitrophenyl)‐1H‐1,2,3‐triazole was active against three human cancer cell lines: MCF‐7, MDA‐MB‐231, and A‐549. Later, the results of the inhibitory assay of potent compounds against the tyrosine kinase epidermal growth factor receptor revealed that compounds 1‐((4‐chlorophenyl)sulfonyl)‐5‐(4‐methoxyphenyl)‐4‐((1‐methyl‐1H‐imidazol‐2‐yl)sulfonyl)‐1H‐1,2,3‐triazole and 1‐((4‐chlorophenyl) sulfonyl)‐4‐((1‐methyl‐1H‐imidazol‐2‐yl) sulfonyl)‐5‐(4‐nitrophenyl)‐1H‐1,2,3‐triazole showed more potency than the reference drug erlotinib.

Construction of Rings via Metal‐Catalyzed C−H Annulation with Unsymmetrical Internal Alkynes: Selectivity and Applications

AbstractSelective and concise construction of ring systems that are ubiquitous skeletons across chemistry, drugs and materials, is indispensable for human life. Of note, directed C−H annulation with alkynes for the expedient delivery of ring systems holds great importance, featuring step‐ and atom‐economy, mild conditions, and broad substrate scope. However, regioselectivity issues remained when using unsymmetrical alkynes for the directed C−H annulation. Herein, we summarized recent achievements towards solving this problem by developing directing groups, metal catalysts, and alkynes with versatile and traceless functionality that ensure the overall regioselectivity, enantioselectivity, efficiency, and synthetic application. We hope this concept will promote the further development of the precise construction of functional molecules using C−H annulation with unsymmetrical alkynes.