Fluoride-mediated phosphination of alkenes and alkynes by silylphosphines

Regioselective phosphination of carbon-carbon unsaturated bonds by a fluoride-mediated reaction of silylphosphines is described. Alkenes and alkynes having a directing group, such as an aromatic or a carbonyl group, reacted to form a carbon-phosphorus bond under mild conditions. When an anhydrous fluoride source was applied in the presence of an electrophile, the corresponding three-component coupling product was obtained.     

Highly Stereoselective and Efficient Hydrosilylation of Terminal Alkynes Catalyzed by

With [RuCl(2)(p-cymene)](2) as a catalyst, extremely high regio- and stereoselectivity was observed in the hydrosilylation reaction of various terminal alkynes under mild conditions to afford beta-(Z)-vinylsilanes in excellent yields. A dramatic directing effect was also observed when alkynes having a hydroxyl group at the beta position to the triple bond were employed as a substrate, and in these cases regioisomeric alpha-vinylsilanes were generated with excellent selectivity.     

New ligand platforms for developing the chemistry of the Ti=N-NR2 functional group and the insertion of alkynes into the N-N bond of a Ti=N-NPh2 ligand

Two broadly applicable strategies for extending the available ligand platforms of the virtually unexplored terminal Ti=N-NR2 functional group are described, along with the highly selective room temperature insertion of alkynes into the N-N bond of Ti{MeN(CH2CH2NSiMe3)2}(NNPh2)(py) and the catalytic cis-diamination of PhC[triple bond]CMe by diphenylhydrazine.     

Copper-catalysed photoinduced decarboxylative alkynylation: a combined experimental and computational study

Redox-active esters (RAEs) as alkyl radical precursors have demonstrated great advantages for C–C bond formation. A decarboxylative cross-coupling method is described to afford substituted alkynes from various carboxylic acids using copper catalysts CuCl and Cu(acac)₂. The photoexcitation of copper acetylides with electron-rich NEt₃ as a ligand provides a general strategy to generate a range of alkyl radicals from RAEs of carboxylic acids, which can be readily coupled with a variety of aromatic alkynes. The scope of this cross-coupling reaction can be further expanded to aliphatic alkynes and alkynyl silanes using a catalytic amount of preformed copper-phenylacetylide. In addition, DFT calculations revealed the favorable reaction pathway and that the bidentate acetylacetonate ligand of the copper intermediate plays an important role in inhibiting the homo-coupling of the alkyne.

Redox-active esters (RAEs) as alkyl radical precursors have demonstrated great advantages for Cu-catalysed C–C bond formation.     

Zinc‐Catalysed Hydroboration of Terminal and Internal Alkynes

A regioselective hydroboration of alkynes has been developed by using commercially available zinc triflate as a catalyst, in the presence of catalytic amount of NaBHEt₃. The reaction tolerates a wide range of terminal alkynes having several synthetically useful functional groups and proceeds regioselectively to furnish hydroborated products in moderate to excellent yields. This system shows moderate chemoselectivity towards terminal C≡C bond over terminal and internal C=C bond and internal C≡C bond.     

Iron‐Carbonyl‐Catalyzed Redox‐Neutral [4+2] Annulation of N−H Imines and Internal Alkynes by C−H Bond Activation

Stoichiometric C?H bond activation of arenes mediated by iron carbonyls was reported by Pauson as early as in 1965, yet the catalytic C?H transformations have not been developed. Herein, an iron‐catalyzed annulation of N?H imines and internal alkynes to furnish cis‐3,4‐dihydroisoquinolines is described, and represents the first iron‐carbonyl‐catalyzed C?H activation reaction of arenes. Remarkablely, this is also the first redox‐neutral [4+2] annulation of imines and alkynes proceeding by C?H activation. The reaction also features only cis stereoselectivity and excellent atom economy as neither base, nor external ligand, nor additive is required. Experimental and theoretical studies reveal an oxidative addition mechanism for C?H bond activation to afford a dinuclear ferracycle and a synergetic diiron‐promoted H‐transfer to the alkyne as the turnover‐determining step.     

Palladium-catalyzed selective cross-addition of triisopropylsilylacetylene to internal and terminal unactivated alkynes

Dinuclear and mononuclear palladium complexes having N,N'-bis[2-(diphenylphosphino)phenyl]amidinate (DPFAM) as a ligand catalyzed the cross-addition of triisopropylsilylacetylene (TIPSA) to unactivated internal alkynes, giving enynes selectively. When palladium catalysts having PPh3, TDMPP, dppe, or dppf were used, dimers of TIPSA were obtained as major products. The reactions of TIPSA with several terminal alkynes also gave cross-adducts selectively, although the yields were moderate.     

Transition-metal-catalyzed carbon-heteroatom three-component cross-coupling reactions: a new concept for carbothiolation of alkynes

The deep-seated understanding of flexible ligand behavior of thiolate on transition-metals has paved the way to achieve metal-catalyzed carbothiolations of terminal alkynes. The strategy of the reaction is quite simple: 1) generation of the complex with C-Pt-S fragments formed after the Pd-catalyzed C-S bond-forming cross-coupling reaction, 2) insertion of an alkyne into Pt-S bond to form the complex with a C-Pt-C fragment, and 3) C-C bond-forming reductive elimination.     

Mechanistic study of palladium catalyzed S-S and Se-Se bonds addition to alkynes

The mechanistic study of palladium catalyzed S-S and Se-Se bonds addition to alkynes revealed the involvement of dinuclear transition metal complexes in the catalytic cycle. Coordination of alkyne to dinuclear transition metal complex was found to be the rate determining step of the reaction. An unusual phosphine ligand effect increasing the yield of addition reaction was found in the studied system. A new synthetic procedure was developed to perform the catalytic reaction using easily available Pd(II) complex. The scope of the reaction and the reactivity of S-S and Se-Se bonds toward alkynes were investigated. The X-ray structure of the product of S-S bond addition reaction showed favorable geometry for the possible application as a chelate ligand.     

The comparison of addition of molecules possessing P(V)-H bond to alkynes catalyzed with Pd and Ni complexes

Main factors have been analyzed necessary for creation of an efficient catalytic system for alkynes hydrophosphorylation based on nickel complexes, and a valid model system was suggested for the comparison with palladium complexes. It has been discovered for the first time that the insertion of an alkyne into the metal-hydrogen bond occurs with a considerably lower activation barrier than into the metal-phosphorus bond, whereas the variation in the reaction energy corresponds in both cases to an exothermic reaction. Under the optimized conditions the transformation catalyzed by nickel complexes does not require acid addition and may proceed even in the absence of a phosphine ligand.     

Reaction of difluorocarbene with propargyl esters and efficient synthesis of difluorocyclopropyl ketones

Difluorocarbene generated from FSO₂CF₂CO₂SiMe₃ (TFDA) at 120 °C could reacted with terminal alkynes having an ester group at the α position to the triple bond. Difluorocyclopropenes were further converted to difluorocyclopropyl ketones under alkaline condition. Mechanism for the conversion was studied.     

Carbon dioxide as a carbon source in organic transformation: carbon-carbon bond forming reactions by transition-metal catalysts

Recent carbon-carbon bond forming reactions of carbon dioxide with alkenes, alkynes, dienes, aryl zinc compounds, aryl boronic esters, aryl halides, and arenes having acidic C-H bonds are reviewed in which transition-metal catalysts play an important role.     

Mechanism of stereoinduction in asymmetric synthesis of highly functionalized 1,2-dihydroquinolines and 2H-1-benzopyrans via nonracemic palladacycles with a metal-bonded stereogenic carbon

To establish the synthetic utility of palladacycles, a stable racemic benzannulated azapalladacycle featuring a palladium-bonded sp(3)-hybridized stereogenic carbon was prepared and converted into a series of racemic 2,3,4-trisubstituted 1,2-dihydroquinolines via a regioselective insertion of activated alkynes (RCCCOOEt). Analogous diastereomerically enriched azapalladacyle (92% de) and oxapalladacycle (64% de) were synthesized from arylpalladium(II) iodo complexes possessing a nonracemic spectator ligand ((1R,2R)-N,N,N',N'-tetramethyl-1,2-diaminocyclohexane) via an intramolecular displacement of the iodide by an ester enolate. Absolute configurations of the metal-bonded stereocenters in the diastereomerically enriched palladacycles were unequivocally assigned, and the efficiency of stereoinduction was systematically studied. On the basis of these experiments, a plausible mechanism for the transfer of chirality from the nonracemic auxiliary ligand to the palladium-bonded stereogenic carbon was proposed. A restricted rotation about the palladium-aryl bond in arylpalladium(II) iodo complexes giving rise to atropisomers, as well as the nature of the leaving group (iodide or acetate), were found to play a crucial role in the chirality transfer process. Diastereomerically enriched palladacycles underwent a ligand exchange with triphenylphosphine followed by regioselective insertion of unsymmetrical alkynes to afford nonracemic 1,2-dihydroquinolines (six examples) in excellent 80-91% ee and 2H-1-benzopyrans (four examples) in 32-56% ee.     

NiCl2-catalyzed hydrophosphinylation

[reaction: see text] A new nickel-based catalytic system has been developed for phosphorus-carbon bond formation. The addition of alkyl phosphinates to alkynes is catalyzed by nickel chloride in the absence of added ligand. The reaction generally proceeds in high yields, even with internal alkynes, which were poor substrates in our previously reported palladium-catalyzed hydrophosphinylation of alkyl phosphinates. The method is useful for the preparation of H-phosphinate esters and their derivatives. The one-pot synthesis of various important organophosphorus compounds is also demonstrated. The reaction can be conducted with microwave heating.     

Three characteristic reactions of alkynes with metal compounds in organic synthesis

Alkynes have two sets of mutually orthogonal π‐bonds that are different from the π‐bonds of alkenes. These π‐bonds are able to bond with transition metal compounds. Alkynes easily bond with the various kinds of compounds having a π‐bond such as carbon monoxide, alkenes, other alkynes and nitriles in the presence of the transition metal compounds. The most representative reaction of alkynes is called the Pauson–Khand reaction. The Pauson–Khand reactions include the cyclization of alkynes with alkenes and carbon monoxide in the presence of cobalt carbonyls. Similar Pauson–Khand reactions also proceed in the presence of other transition metal compounds. These reactions are the first type of characteristic reaction of alkynes. Other various kinds of cyclizations with alkynes also proceed in the presence of the transition metal compounds. These reactions are the second type of characteristic reaction of alkynes. These include cyclooligomerizations and cycloadditions. The cyclooligomerizations include mainly cyclotrimerizations and cyclotetramerizations, and the cycloadditions are [2 + 2], [2 + 2 + 1], [2 + 2 + 2], [3 + 2], [4 + 2], etc., type cycloadditions. Alkynes are fairly reactive because of the high s character of their σ‐bonds. Therefore, simple coupling reactions with alkynes also proceed besides the cyclizations. The coupling reactions are the third type of characteristic reactions of alkynes in the presence of, mainly, the transition metal compounds. These reactions include carbonylations, dioxycarbonylations, Sonogashira reactions, coupling reactions with aldehydes, ketones, alkynes, alkenes and allyl compounds. Copyright © 2008 John Wiley & Sons, Ltd.     

C sp 3-H bond activation triggered by formation of metallacycles: rhodium(I)-catalyzed cyclopropanation/cyclization of allenynes

Giving direction: An C?sp?3-H bond activation directed by a rhodacycle intermediate has been found to occur in a Rh(I)-catalyzed reaction between an allene moiety having a tert-butyl substituent, and tethered alkynes. Cyclic compounds containing a cyclopropane ring were obtained in good to high yields (up to 92%).     

Regioselective alkenylation of imidazoles by nickel/Lewis acid catalysis

Nickel/Lewis acid binary catalysis is found effective to direct regioselective alkenylation of imidazoles through C-H bond activation and stereoselective insertion of alkynes. Use of P(t-Bu)₃ as a ligand allows exclusive regioselective C(2)-alkenylation, while PCyp₃ is found effective for C(5)-alkenylation of C(2)-substituted imidazoles. The reaction demonstrates a broad scope of imidazoles and internal alkynes to give trisubstituted ethenes highly regio- and stereoselectively in modest to good yields.     

Rhodium‐Catalyzed Oxidative Coupling between Salicylaldehydes and Internal Alkynes with C?H Bond Cleavage To Produce 2,3‐Disubstituted Chromones

A direct oxidative coupling of salicylaldehydes with internal alkynes proceeds efficiently with cleavage of the aldehyde C? H bond to produce the corresponding chromone derivatives. A rhodium catalyst in combination with a cyclopentadiene ligand and a copper oxidant promote this straightforward annulation reaction. Solid‐state luminescence was observed for certain chromone products.     

Reactions of coordinated molecules : III. Alkoxy substituent exchange reactions on a cyclic ligand

The extraction of an ethoxide anion from a β-diethylacetal-acyl ligand of a neutral organometallic molybdenum complex affords a cationic complex having a cyclic ligand which is described best as a metal-stabilized oxonium ion. This ligand has an unusually reactive saturated carbon atom which reacts with a variety of alcohols and with ethanethiol via an alkoxy group exchange reaction affording a differently substituted cyclic ligand. The oxidization of the metal—ligand bond in the initial complex forms 4-ethoxy-γ-butyrolactone and, therefore, it is a precursor for the preparation of a variety of 4-substituted-γ-butyrolactones. The reaction of this complex with sodium methoxide and dimethyl sulfoxide is discussed, also.     

Edge-bridging and face-capping coordination of alkenyl ligands in triruthenium carbonyl cluster complexes derived from hydrazines: synthetic, structural, theoretical, and kinetic studies

The reactions of the triruthenium cluster complex [Ru3(mu-H)(mu3-eta2-HNNMe2)(CO)9] (1; H2NNMe2=1,1-dimethylhydrazine) with alkynes (PhC triple bond CPh, HC triple bond CH, MeO2CC triple bond CCO2Me, PhC triple bond CH, MeO2CC triple bond CH, HOMe2CC triple bond CH, 2-pyC triple bond CH) give trinuclear complexes containing edge-bridging and/or face-capping alkenyl ligands. Whereas the edge-bridged products are closed triangular species (three Ru-Ru bonds), the face-capped products are open derivatives (two Ru-Ru bonds). For terminal alkynes, products containing gem (RCCH2) and/or trans (RHCCH) alkenyl ligands have been identified in both edge-bridging and face-capping positions, except for the complex [Ru3(mu3-eta2-HNNMe2)(mu3-eta3-HCCH-2-py)(mu-CO)(CO)7], which has the two alkenyl H atoms in a cis arrangement. Under comparable reaction conditions (1:1 molar ratio, THF at reflux, time required for the consumption of complex 1), some reactions give a single product, but most give mixtures of isomers (not all the possible ones), which were separated. To determine the effect of the hydrazido ligand, the reactions of [Ru3(mu-H)(mu3-eta2-MeNNHMe)(CO)9] (2; HMeNNHMe=1,2-dimethylhydrazine) with PhC triple bond CPh, PhC triple bond CH, and HC triple bond CH were also studied. For edge-bridged alkenyl complexes, the Ru--Ru edge that is spanned by the alkenyl ligand depends on the position of the methyl groups on the hydrazido ligand. For face-capped alkenyl complexes, the relative orientation of the hydrazido and alkenyl ligands also depends on the position of the methyl groups on the hydrazido ligand. A kinetic analysis of the reaction of 1 with PhC[triple chemical bond]CPh revealed that the reaction follows an associative mechanism, which implies that incorporation of the alkyne in the cluster is rate-limiting and precedes the release of a CO ligand. X-ray diffraction, IR and NMR spectroscopy, and calculations of minimum-energy structures by DFT methods were used to characterize the products. A comparison of the absolute energies of isomeric compounds (obtained by DFT calculations) helped rationalize the experimental results.