Thermodynamics of vaporization of gallium trichloride

The unsaturated and saturated pressures of gallium trichloride vapor were measured by the static method with membrane-gauge manometers in wide pressure (0.2–760 Torr) and temperature (313–1071 K) intervals. Scanning calorimetry was used to determine the thermodynamic characteristics of GaCl₃ fusion. The thermodynamic characteristics were obtained for sublimation, fusion, vaporization, and association in the vapor of GaCl₃ molecules. The enthalpies of formation and the absolute entropies of GaCl₃ in the liquid and gaseous phases and Ga₂Cl₆ in the gaseous phase were calculated using literature data. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1266–1269, July, 2007.     

Palladium-catalyzed hydrophosphinylation of alkenes and alkynes

Various palladium catalysts promote the addition of hypophosphorous derivatives ROP(O)H(2) to alkenes and alkynes in good yields and under mild conditions. Particularly, Cl(2)Pd(PPh(3))(2)/2 MeLi, and Pd(2)dba(3)/xantphos allow for phosphorus-carbon bond formation instead of transfer hydrogenation. Commercial aqueous solutions of hypophosphorous acid can be employed successfully at ambient temperature. With styrene and terminal alkynes, the regioselectivity (linear versus branched products) can be controlled to some extent with the catalytic system employed. The methodology considerably extends upon previous routes for the preparation of H-phosphinic acids and other organophosphorus compounds.     

Palladium-catalyzed reaction of phenyl fluoroalkanesulfonates with alkynes and alkenes

Palladium-catalyzed reaction of phenyl fluoroalkanesulfonates with alkynes and alkens under mild conditions gives the corresponding alkynyl and alkenyl substituted benzenes in good yields.     

Cationic palladium-catalyzed hydrosilylative cross-coupling of alkynes with alkenes

A cationic palladium complex-catalyzed cross-coupling of alkynes with alkenes is presented, which occurs selectively under the hydrosilylation conditions using trichlorosilane. The unique reaction might be well understood in terms of an initial hydropalladation of a given 1-alkyne to form regioselectively a 1-alkenylpalladium species, which, in turn, undergoes easily and specifically an alkene insertion. The resulting homoallylic organopalladium species terminates one catalytic cycle by substituting the palladium center with a trichlorosilyl group to give product(s).     

Cobalt-catalyzed reductive coupling of activated alkenes with alkynes

Cobalt complex/Zn systems effectively catalyze the reductive coupling of activated alkenes with alkynes in the presence of water to give substituted alkenes with very high regio- and stereoselectivity in excellent yields. While the intermolecular reaction of acrylates, acrylonitriles, and vinyl sulfones with alkynes takes place in the presence of CoI2(PPh3)2/Zn, the reaction of enones and enals with alkynes requires the use of the CoI2(dppe)/Zn/ZnI2 system. The intramolecular reductive coupling of activated alkenes (enones, enals, acrylates, and acrylonitriles) with alkynes also works efficiently. Further a variety of cyclic lactones and lactams were prepared using this methodology. Possible mechanistic pathways are proposed based on a deuterium-labeling experiment carried out in the presence of D2O.     

Amine-directed intramolecular hydroacylation of alkenes and alkynes

Medium-ring heterocycles are prepared via an amine-directed, rhodium(I)-catalyzed intramolecular hydroacylation. The presence of an allyl substituent on the amine accelerates the reaction and increases product yields.     

Free radical fluoroalkylation of terminal alkenes and alkynes with iododifluoromethanesulfonamides

Free radical fluoroalkylation of terminal alkenes and alkynes with iododifluoromethanesulfonamides has been successfully achieved.It was found that both the catalytic amount of sodium dithionite (Na2S2O4) and the stoichiometric amount of triethylborane (Et3B)/air can efficiently initiate the current free-radical atom transfer reaction.     

FeBr_3-catalyzed dibromination of alkenes and alkynes

The dibromination of alkenes and alkynes with bromosuccinimide and sodium bromide catalyzed by FeBr₃ under mild conditions has been developed.The trans-dibromo compounds were exclusively obtained with excellent yields.     

Recent advances in diphosphination of alkynes and alkenes

1,2-Bis(diphenylphosphino)ethenes and -ethanes (DPPEs) are among representative supporting ligands in transition metal catalysts, which can promote otherwise challenging organic transformations with high efficiency and selectivity. Such bidentately coordinating ligands are conventionally prepared by nucleophilic substitution reactions of halogenated carbon electrophiles with nucleophilic metal phosphides. However, they suffer from poor functional group compatibility and/or tedious preparation of highly functionalized starting substrates. In this context, additions of phosphines to readily available and simple alkynes and alkenes have recently received significant attention. This digest paper focuses on recent developments of diphosphination of alkynes and alkenes for the synthesis of DPPE-type ligands. The reported approaches are categorized into several types of reactions, and their scope, limitation, and mechanism are briefly summarized.     

Brønsted acid-promoted cyclizations of siloxy alkynes with unactivated arenes, alkenes, and alkynes

In this article, we describe the development of a general concept for the development of new carbon-carbon bond-forming processes, which is based on Brønsted acid-mediated activation of a siloxy alkyne, followed by efficient interception of the resulting highly reactive ketenium ion by unactivated arenes, alkenes or alkynes. We found that trifluoromethane sulfonimide (HNTf₂) proved to be a superior promoter of these reactions compared to a range of other Brønsted acids. This finding could be attributed to a high acidity of HNTf₂ in aprotic organic solvents combined with a low nucleophilicity of the NTf₂⁻ anion. Depending on the nature of the nucleophile, the carbocyclizations proceeded either via 6-endo-dig or 5-endo-dig manifolds. In the case of 1-siloxy-1,5-diynes, the cyclizations occurred with a concomitant halide abstraction or arylation.     

Cobalt- and nickel-catalyzed regio- and stereoselective reductive coupling of alkynes, allenes, and alkenes with alkenes

Transition-metal-catalyzed coupling of two different C-C pi components through a metallacycle intermediate is a highly atom economical method to construct C-C bonds in organic synthesis. The metal-catalyzed coupling of an alkene and alkyne generally gives an Alder-ene or reductive coupling product. In this article, we focus on the cobalt- and nickel-catalyzed reductive coupling of alkynes, allenes, and alkenes with alkenes. These reductive coupling reactions provide convenient methods for the synthesis of various alkenes, dienes, functionalized alkanes, lactones, lactams, and cyclic alcohols in a highly regio- and stereoselective manner. A chemselective formation of metallacyclopentene intermediate from the two different C-C pi components and a low-valence metal species plays a key role for the high regio- and stereoselectivity of the catalytic reaction.     

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.     

Stereoselective halogenations of alkenes and alkynes in ionic liquids

[reaction: see text]. Room-temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bromide, and 1-butyl-3-methylimidazolium chloride, are used as "green" recyclable alternative to chlorinated solvents for the stereoselective halogenation of alkenes and alkynes.     

Polar addition of perfluoro-tert-hexyl iodide to alkenes and alkynes

The effective charges on the atoms in molecules of perfluoroalkyl halides of general formula (CF₃)_nCF_3–nX (X=Cl, Br, I) have been calculated by the AM1 semiempirical method. In polar solvents perfluoro-tert-hexyl iodide is reduced under the action of alkenes and aromatic hydrocarbons to form 2-hydroperfluoro-2-methyl-pentane and perfluoro-2-methyl-2-pentene. In ethyl acetate the regio- and stereo-specific addition of perfluoro-tert-hexyl iodide to alkenes, butadiene, and alkynes takes place, which is associated with the realization of a polar ion-radical mechanism for the reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2057–2061, September, 1989.     

Novel amine-catalysed hydroalkoxylation reactions of activated alkenes and alkynes

Substoichiometric loadings of DBU catalyse the efficient 1,4-addition of alcohols and non-nucleophilic amines such as pyrrole to activated alkenes; the application of this methodology in a one-pot synthesis of a natural product, and as a novel strategy for the synthesis of mono-protected 1,3-carbonyl compounds is reported.