Cross-coupling reactions of arylsilanols with substituted aryl halides

[reaction: see text] The palladium-catalyzed cross-coupling of arylsilanols with aryl iodides and aryl bromides (in the presence of cesium carbonate) furnished various biaryl products in high yield. An extensive series of optimizations led to the identification of key variables, including activator, solvent, catalyst, and hydration level, that influence the rate and selectivity of the process. Manipulation of these features provided an effective coupling method of wide scope and generality.     

Formation of phenylmagnesium halides in toluene

Formation reactions of phenylmagnesium chloride and bromide in toluene in the presence of one or two equivalents of diethyl ether or THF were investigated kinetically. Also, the reaction in diethyl ether and in chlorobenzene was addressed. Kinetic features of the reactions are similar to those found previously for the formation of alkylmagnesium halides in toluene and consist of rapid formation of a disolvated Grignard reagent followed by a slower formation of a monosolvated reagent. The latter is able of catalyzing the conversion of different halides into Grignard reagents. However, the contribution of Wurtz-type side reactions is considerable except when THF is used in toluene. Involving the kinetic data and the activation parameters some details of the reaction mechanism were discussed.     

Cross-coupling reactions of (1-fluorovinyl)methydiphenylsilane(1) with aryl halides and aryl triflates

The cesium fluoride (CsF)-assisted cross-coupling reaction of (1-fluorovinyl)methyldiphenylsilane (1) with aryl halides and aryl triflates was examined. The reaction with aryl iodides smoothly proceeded to afford the corresponding (1-fluorovinyl)arenes in the presence of a catalytic amount of CuI and Pd(PPh(3))(4) in aprotic polar solvents such as DMF, DMI, DMA, and NMP in good yields. A variety of functional groups (nitro, ester, ketone, and ether) on the aromatic rings can be tolerated under these mild conditions. Aryl iodides are superior to aryl bromides as the coupling reaction partner. The cross-coupling reaction of 1 with aryl triflates instead of aryl halides was also accomplished in the presence of tetrabutylammonium iodide (n-Bu(4)NI) as the additive under similar conditions.     

Cross-coupling reactions of alkenylsilanols with fluoroalkylsulfonates

[reaction: see text] The design and development of an effective protocol for the palladium-catalyzed cross-coupling of (E)- and (Z)-heptenyldimethylsilanols with organo-triflates and nonaflates is described. Optimization of this coupling focused on the issues of both reactivity and stability of the psuedohalides in the presence of the nucleophilic fluoride promoter for the coupling. The crucial role of varying amounts of water to modulate the reactivity of the fluoride ion is highlighted.     

Cross-coupling of alkynylsilanols with aryl halides promoted by potassium trimethylsilanolate

The palladium-catalyzed cross-coupling of aliphatic alkynylsilanols with aryl iodides has been demonstrated with potassium trimethylsilanolate as the coupling promoter and copper(I) iodide as a cocatalyst. The cross-coupling proceeds at room temperature in good to excellent yield with a range of aryl iodides. A comparison of the reactivity of alkynylsilanols, trimethylsilylalkynes, and terminal alkynes under fluoride and fluoride-free conditions was performed to elucidate the role of silicon in the Sonogashira reaction.     

Cross-coupling reactions of aryl pivalates with boronic acids

The first cross-coupling of acylated phenol derivatives has been achieved. In the presence of an air-stable Ni(II) complex, readily accessible aryl pivalates participate in the Suzuki-Miyaura coupling with arylboronic acids. The process is tolerant of considerable variation in each of the cross-coupling components. In addition, a one-pot acylation/cross-coupling sequence has been developed. The potential to utilize an aryl pivalate as a directing group has also been demonstrated, along with the ability to sequentially cross-couple an aryl bromide followed by an aryl pivalate, using palladium and nickel catalysis, respectively.     

Exchange reactions of hydrogen halides with hydrogenic atoms

Calculations on the D + HBr → DBr + H and D + HI → DI + H reactions are reported. A three-dimensional, quantum-dynamical approximation is used which involves applying the energy sudden approximation to the entrance channel hamiltonian and the centrifugal sudden approximation to the exit channel hamiltonian. Results of integral and differential cross sections, rate coefficients and rotational distributions are presented. Diatomics-in-molecules potential-energy surfaces have been used in the computations. The HBrH potential has been optimesed so that the calculated room-temperature rate coefficient agrees with experiment. This potential has a barrier height of 0.237 eV. Rate coefficient computations for the four reactions H′ + H″ Cl → - H′Cl + H″ (H′, H″ = H or D) are also reported. These results, for a LEPS surface, agree well with those obtained in quasiclassical trajectory and variational transition state theory calculations.     

Silver-catalyzed coupling reactions of alkyl halides with indenyllithiums

Coupling reactions of tertiary and secondary alkyl halides with indenyllithiums proceeded effectively in the presence of a catalytic amount of silver bromide to provide tertiary- and secondary-alkyl-substituted indene derivatives in good yields.     

Photochemical reactions of acyl iodides with aryl halides

Photochemical reactions of acyl iodides RC(O)I (R = Me, Ph) with aryl halides, fluoro-, chloro-, and bromobenzenes, 1,4-dibromobenzene, 2- and 3-bromotoluenes, and 4-bromo-1,2-dimethylbenzene, were studied. Acetyl iodide reacted with chloro- and bromobenzenes and 1,4-dibromobenzene according to the exchange pattern to give iodobenzene and 1,4-diiodobenzene, respectively. No halogen exchange was observed in the reactions of acetyl iodide with fluorobenzene and hexafluorobenzene. Benzoyl iodide failed to react with chloro- and brombenzene under UV irradiation but underwent polycondensation with formation of black nonfusible oligomers which were found to possess paramagnetic and semiconducting properties. Ultraviolet irradiation of a mixture of MeCOI with 2- or 3-bromotoluene, as well as with 4-bromo-1,2-dimethylbenzene, also led to the formation of polymeric products as a result of polycondensation of aryl iodides formed initially via replacement of bromine by iodine. Irradiation of benzoyl iodide in 2- or 3-bromotoluene involved recombination of benzoyl radicals to give benzil as the only product.     

Kumada-Corriu reactions of alkyl halides with alkynyl nucleophiles

[reaction: see text] Pd(2)(dba)(3)-Ph(3)P-catalyzed Kumada-Corriu coupling reactions of unactivated alkyl bromides or iodides with an alkynyl nucleophile furnish C(sp)-C(sp)3 bond formation. Alkynyl nucleophiles can be alkynyllithiums or the corresponding Grignard reagents. The superior performance of Ph(3)P ligand over the trialkylphosphine ligands indicates that this cross-coupling reaction may be a reductive-elimination-controlled process.     

Cross-coupling reaction of alpha-chloroketones and organotin enolates catalyzed by zinc halides for synthesis of gamma-diketones

The reaction of tin enolates 1 with alpha-chloro- or bromoketones 2 gave gamma-diketones (1,4-diketones) 3 catalyzed by zinc halides. In contrast to the exclusive formation of 1,4-diketones 3 under catalytic conditions, uncatalyzed reaction of 1 with 2 gave aldol-type products 4 through carbonyl attack. NMR study indicates that the catalyzed reaction includes precondensation between tin enolates and alpha-haloketones providing an aldol-type species and their rearrangement of the oxoalkyl group with leaving halogen to produce 1,4-diketones. The catalyst, zinc halides, plays an important role in each step. The carbonyl attack for precondensation is accelerated by the catalyst as Lewis acid and the intermediate zincate promotes the rearrangement by releasing oxygen and bonding with halogen. Various types of tin enolates and alpha-chloro- and bromoketones were applied to the zinc-catalyzed cross-coupling. On the other hand, the allylic halides, which have no carbonyl moiety, were inert to the zinc-catalyzed coupling with tin enolates. The copper halides showed high catalytic activity for the coupling between tin enolates 1 and organic halides 7 to give gamma,delta-unsaturated ketones 8 and/or 9. The reaction with even chlorides proceeded effectively by the catalytic system.     

Oxidation-reduction reactions of dicylcopentadienylvanadium halides

Conclusions Vanadocene and a dicyclopentadienylvanadium monohalide are oxidized under mild conditions by either AgCl or organic halides to dicyclopentadienylvanadium dihalides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No.5, pp. 1144–1145, May, 1979.     

Coupling reactions of aryl and heteroaryl halides with a trimethylsilylethynylpyrazine

By the coupling reactions of trimethylsilylacetylene and 2-chloro-3,6-diisobutylpyrazine, 3,6-diisobutyl-2-trimethylsilylethynylpyrazine or 1,2-bis(3,6-diisobutylpyrazin-2-yl)acetylene was obtained, depending on the solvent used. The former substance coupled with various aryl and heteroaryl halides to give 1-aryl-2-pyrazin-ylacetylenes.     

Copper-catalyzed cross-coupling reactions of non-activated primary,secondary or tertiary alkyl chlorides with phenylmagnesium bromide

Efficient copper-catalyzed cross-coupling reactions of non-activated alkyl chlorides, including primary, secondary, and tertiary alkyl chlorides, with phenyl Grignard reagents were achieved. Preparation of phenylmagnesium bromide in 2-methyltetrahydrofuran is critical for the success of the reaction. This protocol expands the synthetic toolbox for the construction of CC bonds of non-activated primary, secondary, and tertiary alkyl chlorides via copper-catalyzed cross-coupling.     

Catalysts for cross-coupling reactions with non-activated alkyl halides

Despite the problems inherent to metal-catalyzed cross-coupling reactions with alkyl halides, these reactions have become increasingly important during the last few years. Detailed mechanistic investigations have led to a variety of novel procedures for the selective cross-coupling of non-activated alkyl halides bearing beta hydrogen atoms with a variety of organometallic nucleophiles under mild reaction conditions. This Minireview highlights selected examples of metal-catalyzed coupling methods and is intended to encourage chemists to exploit the potential of these approaches in organic synthesis.