Nickel-catalyzed alkenylation

Fig. 16.10. Nickel-catalyzed alkenylation of Grignard compounds occurrence of stereoselectivity and stereospecificity.

Scheme 9 Nickel-catalyzed alkenylation of pyridine JV-oxide using alkynes...

SCHEME 5.11 Nickel-catalyzed alkenylation of heteroarenes with alkynes. 

SCHEME 5.12 Nickel-catalyzed alkenylation of 1,3,4-oxadiazoles with alkynes. 

SCHEME 5.13 Nickel-catalyzed alkenylation of pyridine A -oxides with alkynes. 

SCHEME 5.15 Nickel-catalyzed alkenylation of six-membered heteroarenes. 

Synthesis of substituted isoquinolines via nickel-catalyzed alkenylation of... 

While aryl halides are the most common electrophiles in the C-H activation of heterocycles, new methods involving other electrophiles are gradually appearing in the literature. For example, the nickel-catalyzed alkenylation of V-methyl imidazole with diphenylacetylene has been accomplished in the presence of tri-ferf-butylphosphine and trimethylaluminum (eq 23). Tri-ferf-butylphosphine provided better yields of the C2 alkenylation product than tricyclohexyl and triphenylphosphine. Seven examples were reported with yields ranging from 53 to 75% and E.Z selectivities up to >99 1. 

Pretreatment with nickel bromide causes normally unreactive aryl chlorides to undergo Pd-catalyzed substitution,139 and aryl and vinyl triflates have been found to be excellent substrates for Pd-catalyzed alkenylations.140... 

Most studies on nickel-catalyzed domino reactions have been performed by Ikeda and colleagues [287], who observed that alkenyl nickel species, obtained from alkynes 6/4-41 and a (jr-allyl) nickel complex, can react with organometallics as 6/4-42. If this reaction is carried out in the presence of enones 6/4-43 and TM SCI, then coupling products such as 6/4-44 are obtained. After hydrolysis, substituted ketones 6/4-45 are obtained (Scheme 6/4.12). With cyclic and (5-substituted enones the use of pyridine is essential. Usually, the regioselectivity and stereoselectivity of the reactions is very high. On occasion, alkenes can be used instead of alkynes, though this is rather restricted as only norbornene gave reasonable results [288]. 

Tamao and Ito proposed a mechanism for the nickel-catalyzed cyclization/hydrosilylation of 1,7-diynes initiated by oxidative addition of the silane to an Ni(0) species to form an Ni(ii) silyl hydride complex. Gomplexation of the diyne could then form the nickel(ii) diyne complex la (Scheme 1). Silylmetallation of the less-substituted G=C bond of la, followed by intramolecular / -migratory insertion of the coordinated G=G bond into the Ni-G bond of alkenyl alkyne intermediate Ila, could form dienylnickel hydride intermediate Ilia. Sequential G-H reductive elimination and Si-H oxidative addition would release the silylated dialkylidene cyclohexane and regenerate the silylnickel hydride catalyst (Scheme 1). 

Phenylurefbanes, 58, 10 Phosgene, 57, 46 Phosphine, diphenyl-, 56,45 Phosphine-mckcl catalyst, 58, 129 PHOSPHINE-NICKEL CATALYZED COMPLEX CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES, 58, 127 Phosphine, phenyl-, bis(3-dimethylamino-piopyl)-, 55, 128 Phosphine, triphenyl-, 56, 81 Phosphomum, [ 4-(4-rne thoxy phenyl)-2-butenyl) triphenyl, iodide, 56, 81 Phosphomum, 2-octadecenyltnphenyl-, iodide, 56, 81... 

Baba, S., Negishi, E. A novel stereospecific alkenyl-alkenyl cross-coupling by a palladium- or nickel-catalyzed reaction of alkenylalanes with alkenyl halides. J. Am. Chem. Soc. 1976, 98, 6729-6731. 

Other coupling partners to organozinc reagents include heterocyles such as 2-methylthiobenzothiazole, alkenyl aryl iodonium triflates (alkenyl group transfer for synthesis of trisubstituted alkenes), and aryl heteroaryl ethers. " Improved nickel-catalyzed cross-coupling conditions between oz-rto-substituted aryl iodides-nonaflates and alkyl-zinc iodides in. solution and in the solid phase have been defined. ... 

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