Nickel-catalyzed transformation

The nickel-catalyzed transformation of aromatic halides into the corresponding nitriles by reaction with cyanide ions is reported. Both tris(triarylphosphine)nickel(0) complexes and tY2ins-chloro( aryl )bis( triarylphosphine )nickel(II) complexes catalyze the reaction. The influence of solvents, organophos-phines, and substituents on the aromatic nucleus on catalytic cyanation is studied. A mechanism of the catalytic process is suggested based on the study of stoichiometric cyanation of ti3ins-chloro(aryl)bis(triphenylphosphine)nickel-(II) complexes with NaCN and the oxidative addition reaction of Ni[P(C6H5)3]s with substituted aryl halides. 

Nickel-catalyzed transformations of SCBs have been studied by Oshima and co-workers <20060L483>. Nickel-catalyzed ring opening of SCBs with aldehydes affords the corresponding alkoxyallylsilanes (Scheme 55). This transformation represents a hydrosilane-free reductive silylation of aldehydes. A wide range of aldehydes (aliphatic, aromatic, electron-rich, and electron-deficient) can be converted to akoxyallylsilanes. 

The synthesis of chiral racemic atropisomeric pyridines by cobalt-catalyzed [2 + 2 + 2] cycloaddition between diynes and nitriles was reported in 2006 by Hrdina et al. using standard CpCo catalysts [CpCo(CO)2, CpCo(C2H4)2, CpCo(COD)] [34], On the other hand, chiral complexes of type II were used by Gutnov et al. in 2004 [35] and by Hapke et al. in 2010 [36] for the synthesis of enantiomerically enriched atropisomers of 2-arylpyridines (Scheme 1.18). This topic is described in detail in Chapter 9. It is noteworthy that the 2004 paper contains the first examples of asymmetric cobalt-catalyzed [2 - - 2 - - 2] cycloadditions. At that time, it had been preceded by only three articles dealing with asymmetric nickel-catalyzed transformations [37]. Then enantioselective metal-catalyzed [2 -i- 2 - - 2] cycloadditions gained popularity, mostly with iridium- and rhodium-based catalysts, as shown in Chapter 9. 

DEVELOPMENT OF THE STEREOSELECTIVE NICKEL-CATALYZED TRANSFORMATION OF GLYCOSYL TRICHLOROACETEMIDATES TO TRICHLOROACETAMIDES... 

FIGURE 15.20 Nickel-catalyzed transformation of monosaccharide trichloroacetimidates. 

FIGURE 15.22 Nickel-catalyzed transformation of oligosaccharide trichloroacetimidates. 

MECHANISTIC STUDIES ON THE NICKEL-CATALYZED TRANSFORMATION OF GLYCOSYL TRICHLORACETIMIDATES... 

FIGURE 15.27 Proposed mechanism of nickel-catalyzed transformation of trichloroacetim-idate. 

The recent applications of NHCs in ruthenium-catalyzed olefin metathesis and palladium/nickel-catalyzed coupling reactions show the value of such a profound understanding about ligand properties before using them for specific catalytic transformations. 

Stereoselective) additions of nucleophiles to 5-alkylidene Meldmm s acid as displayed in Scheme 17 (Section 8.11.6.1.3) <2006TA2957, 2007AGE4964> and to the carbonyl group of 2,2-dimethyl-l,3-dioxan-5-one (Scheme 47, Section 8.11.6.3.3) either in a three component transformation <2006OL3689> or in a nickel-catalyzed reaction... 

Formally copper catalyzed couplings are analogous to palladium and nickel catalyzed reactions. Carbon-carbon and carbon-heteroatom bonds can be formed in such transformations alike. From the mechanistic point of view there is a significant difference between nickel, palladium and copper catalyzed processes however. While in the former cases the catalyst usually oscillates between the 0 and +2 oxidation states, in copper mediated transformations the common oxidation numbers are +1, +2 and +3. 

Extensive research in the field led to the publication of several reviews and monographs in the field. The place of our book in this niche is to provide an overview of the developments in the application of palladium, nickel and copper catalyzed transformations in the preparation and functionalization of heterocyclic compounds. Although preference was given to recent results, important examples of earlier (pioneering) works are also included in this monograph. 

It includes the steam reforming of methane over a nickel catalyst to synthesis gas followed by the copper-catalyzed transformation of the latter to methanol (see Section 3.5.1). Finally, formaldehyde is produced by oxidative dehydrogenation of methanol. 

There is a substantial body of literature on the palladium- and nickel-catalyzed formation of aryl sulfides, selenides, and phosphines from aromatic and heteroaromatic halides. Progress on these reactions has continued with several recent contributions [47-50]. A review in 1997 covered the types of transformations that can be conducted and the types of catalysts used [51]. Particularly useful examples are the conversions ofbinaphthol to binaphthylphosphines... 

The first indication, reported in 1971, for a nickel-catalyzed intramolecular allylation of an alkenic bond was the dimerization of butadiene to 2-methylvinylcyclopentane (263). This efficient transformation (90%) proceeded with 1.2 mol % of a Ni catalyst (prepared in situ from (Bu3P)2NiBr2 and BuLi) in the presence of methanol and presumably involves a nickel-ene reaction of (262) followed by a -elimi-nation of Ha (Scheme 55). 

The nickel-catalyzed intramolecular [4 -i- 4] cycloaddition strategy has been successfully applied to the construction of both the ab and bc ring systems of the taxane diteipenes. These studies ditionally served to establish the viability of this chemistry for the construction of angularly alkyl-substituted bicy-clo[6.4.0]dodecanes. In an example typical of this class of transformations (Scheme 16), cyclooctadiene (125) was produced with greater than 97% diastereoselectivity and in 92% chemical yield when tetraene... 

Annulation of 2-cycloalkenones by the nickel-catalyzed method has proven to be very problematic, although recently a procedure employing triethylborane as a Lewis acid has been successful in additions to 2-cyclopentenone50. The following examples illustrate this transformation. 

The nickel(0)-catalyzed transformation is, however, less useful in this instance, with very poor yields obtained with the Z-ester and isomeric mixtures of type B codimerization products with the -isomer. 

In recent decades much effort has been devoted to extending the scope of palladium, copper, and nickel-catalyzed reactions proceeding via aryl or vinyl metal intermediates [12]. These coupling reactions have enabled the formation of many kinds of carbon-carbon and carbon-heteroatom connections that were previously very difficult to realize. Metal-mediated transformations have proven especially valuable for introduction of substituents to aromatic core structures. They allow the presence of a wide variety of functional groups and perform equally well in both inter and intramolecular applications. Furthermore, in homogeneous catalysis,... 

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