Nickel-catalyzed Heck-type reactions of benzyl chlorides and simple olefins

Enantiospecific intramolecular Heck reactions of secondary benzylic ethers

Enantioenriched methylenecyclopentanes are synthesized by stereospecific, nickel-catalyzed Heck cyclizations of secondary benzylic ethers. The reaction proceeds in high yield and enantiospecificity for benzylic ethers of both π-extended and simple arenes. Ethers with pendant 1,2-disubstituted olefins form trisubstituted olefins with control of both absolute configuration and alkene geometry. Diastereoselective synthesis of a polycyclic furan is demonstrated.

Nickel-catalyzed Mizoroki-Heck reaction of aryl sulfonates and chlorides with electronically unbiased terminal olefins: high selectivity for branched products

Achieving high selectivity in the Heck reaction of electronically unbiased alkenes has been a longstanding challenge. Using a nickel-catalyzed cationic Heck reaction, we were able to achieve excellent selectivity for branched products (≥19:1 in all cases) over a wide range of aryl electrophiles and aliphatic olefins. A bidentate ligand with a suitable bite angle and steric profile was key to obtaining high branched/linear selectivity, whereas the appropriate base suppressed alkene isomerization of the product. Although aryl triflates are traditionally used to access the cationic Heck pathway, we have shown that, by using triethylsilyl trifluoromethanesulfonate, we can effect a counterion exchange of the catalytic nickel complex, such that cheaper and more stable aryl chlorides, mesylates, tosylates, and sulfamates can be used to yield the same branched products with high selectivity.

Copper-catalysed direct radical alkenylation of alkyl bromides

A copper-catalysed direct radical alkenylation of benzyl bromides and α-carbonyl alkyl bromides has been developed. Compared with recent radical alkenylations which mostly focused on secondary or tertiary alkyl halides, this transformation shows good reactivity towards primary alkyl halides and tertiary/secondary alkyl halides are also tolerated.

Copper-catalyzed Hiyama cross-coupling using vinylsilanes and benzylic electrophiles

Copper-catalyzed cross-coupling of vinylsiloxanes with benzyl bromides allowing a mild and simple access to important allyl arene compounds.

Palladium-catalyzed intermolecular Heck reaction of alkyl halides

An efficient Pd-catalyzed method for intermolecular Heck reaction of common alkyl halides is described for the first time.

Synthesis of arylacetonitrile derivatives: Ni-catalyzed reaction of benzyl chlorides with trimethylsilyl cyanide under base-free conditions

A simple and practical method of cyanation of benzyl chlorides and trimethylsilyl cyanide was achieved, using the Ni(cod)₂/PPh₃ catalyst system, to give arylacetonitriles.

Transition-metal-catalyzed laboratory-scale carbon-carbon bond-forming reactions of ethylene

Ethylene, the simplest alkene, is the most abundantly synthesized organic molecule by volume. It is readily incorporated into transition-metal-catalyzed carbon-carbon bond-forming reactions through migratory insertions into alkylmetal intermediates. Because of its D2h symmetry, only one insertion outcome is possible. This limits byproduct formation and greatly simplifies analysis. As described within this Minireview, many carbon-carbon bond-forming reactions incorporate a molecule (or more) of ethylene at ambient pressure and temperature. In many cases, a useful substituted alkene is incorporated into the product.

Synthesis and characterization of coordinatively unsaturated nickel(II) and manganese(II) alkyl complexes supported by the hydrotris(3-phenyl-5-methylpyrazolyl)borate (Tp(Ph,Me)) ligand

The synthesis of several nickel(II) and manganese(II) alkyl complexes supported by hydrotris(3-phenyl-5-methylpyrazolyl)borate (Tp(Ph,Me)) ligand is reported. The metal halide complexes Tp(Ph,Me)MnCl(CH3CN) (1) and Tp(Ph,Me)NiCl (4) were used as precursors for synthesis of Tp(Ph,Me)MnCH2Si(Me)3 (2), Tp(Ph,Me)MnCH2Ph (3), Tp(Ph,Me)NiCH2Si(Me)3 (5) and Tp(Ph,Me)NiCH2Ph (6). The resulting Mn(II) and Ni(II) alkyl complexes, 2-3 and 5-6, were characterized by X-ray crystallography, NMR spectroscopy, and FT-IR spectroscopy. X-ray crystallographic analysis revealed distorted tetrahedral geometries for complexes 2-3 and 5 with a κ(3)-Tp(Ph,Me). Complex 6, on the other hand, was found to have a distorted square planar geometry with κ(2)-Tp(Ph,Me) and an η(3)-benzyl ligand. Transformations of 4 and Tp(Ph,Me)CoCl (10) via treatment with NaN3 to yield Tp(Ph,Me)NiN3 (11), Tp(Ph,Me)CoN3 (12), along with the synthesis of (Tp(Ph,Me))2Ni (8) and Tp(Ph,Me)NiCl(3-Ph-5MepzH) (9) are also reported.

Recent catalytic approaches to chemical synthesis from carbon feedstocks

Traditional organic synthesis is driven by the need for functional molecules. The development of green chemical methods, however, is an increasingly important challenge in the context of global sustainability. To this end, the direct use of abundant carbon feedstocks in synthesis (such as CO, CO2, methanol, arenes, alkanes, α-olefins, and biological raw materials) aims to minimize waste production and increase efficiency.

Simplifying nickel(0) catalysis: an air-stable nickel precatalyst for the internally selective benzylation of terminal alkenes

The synthesis and characterization of the air-stable nickel(II) complex trans-(PCy(2)Ph)(2)Ni(o-tolyl)Cl is described in conjunction with an investigation of its use for the Mizoroki-Heck-type, room temperature, internally selective coupling of substituted benzyl chlorides with terminal alkenes. This reaction, which employs a terminal alkene as an alkenylmetal equivalent, provides rapid, convergent access to substituted allylbenzene derivatives in high yield and with regioselectivity greater than 95:5 in nearly all cases. The reaction is operationally simple, can be carried out on the benchtop with no purification or degassing of solvents or reagents, and requires no exclusion of air or water during setup. Synthesis of the precatalyst is accomplished through a straightforward procedure that employs inexpensive, commercially available reagents, requires no purification steps, and proceeds in high yield.

Iron-containing mesoporous aluminosilicate catalyzed direct alkenylation of phenols: Facile synthesis of 1,1-diarylalkenes

The addition of phenols to aryl-substituted alkynes to form 1,1-diarylalkenes was carried out by using the Fe-Al-MCM-41 catalyst. The catalyst showed remarkable improvement in time and yield in comparison to other solid catalysts. The heterogeneous catalyst can be reused at least three times without a significant loss in activity.

Nickel-catalyzed cross couplings of benzylic ammonium salts and boronic acids: stereospecific formation of diarylethanes via C-N bond activation

We have developed a nickel-catalyzed cross coupling of benzylic ammonium triflates with aryl boronic acids to afford diarylmethanes and diarylethanes. This reaction proceeds under mild reaction conditions and with exceptional functional group tolerance. Further, it transforms branched benzylic ammonium salts to diarylethanes with excellent chirality transfer, offering a new strategy for the synthesis of highly enantioenriched diarylethanes from readily available chiral benzylic amines.

Catalyst-controlled regioselectivity in the synthesis of branched conjugated dienes via aerobic oxidative Heck reactions

Pd-catalyzed aerobic oxidative coupling of vinylboronic acids and electronically unbiased alkyl olefins provides regioselective access to 1,3-disubstituted conjugated dienes. Catalyst-controlled regioselectivity is achieved by using 2,9-dimethylphenanthroline as a ligand. The observed regioselectivity is opposite to that observed from a traditional (nonoxidative) Heck reaction between a vinyl bromide and an alkene. DFT computational studies reveal that steric effects of the 2,9-dimethylphenanthroline ligand promote C-C bond formation at the internal position of the alkene.

Palladium-catalyzed 1,1-difunctionalization of ethylene

The 1,1-difunctionalization of ethylene, with aryl/vinyl/heteroaryl transmetalating agents and vinyl electrophiles, is reported. The reaction is high-yielding under a low pressure of ethylene, and regioselectivity is generally high for the 1,1-disubstituted product. The process is highlighted by the use of heteroaromatic cross-coupling reagents, which have not been competent reaction partners in previously reported efforts.