Nickel-catalyzed addition

Scheme 7.8. Nickel-catalyzed 1,4-addition, using alkene hydroboration and boron-zinc exchange.

Substituted pyridylmethanols 3.72 have been recommended as ligands in nickel-catalyzed 1,4-additions of Et2Zn to a,P-unsaturated carbonyl compounds [112, 972], Asymmetric [2+2+2] cycloadditions of norbomene and acetylenes are catalyzed by a CotyZn/phosphine system and the most efficient ligands are amido-phosphinephosphinites prepared from (S)-valinol 1.60 (R = i-Pr, R = H) [973]. 

Nickel chloride I zinc I pyridine Nickel-catalyzed 1,4-addition to acrylic acid esters... 

Aside from the titanium-mediated process described above, the asymmetric addition of aUcyl groups to aldehydes can also be performed by nickel catalysts. This traces back to seminal work of Fujisawa et al. who had found that the addition of AlMc3 to aldehydes can be catalyzed by Ni(acac)2 and is strongly accelerated by phosphines and phosphites [50]. Racemic additions to aromatic and aliphatic aldehydes thus occurred in good yields with as little as 0.1 mol% of nickel. Interestingly, the reaction with AlEt3 and Al(/Bu)3 predominantly led to the respective addition products with only small amounts of the reduced primary alcohols. This is in contrast to the nickel-catalyzed 1,4-addition of higher aluminum trialkyls to enones, in which the rate of p-hydride elimination surpasses that of 1,4-addition [51]. 

FIGURE 2. The mechanism of the nickel-catalyzed addition of hydrogen cyanide to 1,3-cyclohexa-diene. Reproduced by permission of the Royal Society of Chemistry from Reference 46... 

In an extension of an early work on the nickel-catalyzed addition of hydrogen cyanide to unsaturated compounds, a basic reaction in various large-scale processes in the polymer industry, the hydrocyanation of butadiene (equation 15) and the efficiency of catalysis of this reaction by low-cost copper salts has been studied extensively by Belgium researchers47,48. 

Scheme 75 Homoallyl alcohol by nickel-catalyzed addition of methallyl chloride to carbonyl...

The previous sections described synthetic methods involving palladium- and nickel-catalyzed additions of alcohols and amines to aryl halides and triflates. The development of procedures and catalysts used in these processes has occurred hand-in-hand with mechanistic analysis of the amination chemistry. The following sections describe the current understanding of why these procedures and catalysts are effective, and how this understanding led to some of the breakthroughs described above. 

Nickel-Catalyzed Addition of Grignard Reagents Ring-Opening Reactions with Nucleophiles... 

Since organoaluminum compounds have been known to add to a,) -unsaturated ketones, it is feasible that cyclopropyl ketones can react in a similar fashion. The nickel-catalyzed addition of trimethylaluminum to aryl cyclopropyl ketones 1 yielded the corresponding 1-arylpentanones 2 in moderate yields. It has been postulated that the first step of this reaction involves the nickel(0)-promoted electrophilic attack of alumimun at the carbonyl oxygen. 

An enyne group that is introduced to the p-position of an enone in the nickel-catalyzed addition is generated from alkynylzincation. - ... 

An enyne group is introduced to the P-position of an enone 71 in the nickel-catalyzed addition onto the product generated from alkynylzincation 70 (Scheme 7.27). 

Scheme 7.39 Nickel-catalyzed addition of organoboronates to aldehydes using alkynes as activators as...

Scheme 7.40 Nickel-catalyzed addition to ketones and aldehydes, as reported by Bouffard and Itami [58].

Elmoghayar MRH, Groth P, Undheim K (1983) Nickel-catalyzed addition or coupling reactions of Grignard reagents with halopyrimidines. Acta Chem Scand B 37 109-114... 

Beletskaya reported one of the first examples of the palladium- and nickel-catalyzed addition of secondary phosphines to styrene derivatives (Scheme 4.14 and Example 4.15) [56], Conunon palladium and nickel catalysts such as Pd(NCMe)2Cl2 and Ni[P(OEt)3] promoted the addition reaction, and excellent yields of the addition products were obtained. 

SCHEME 4 24 Nickel-catalyzed addition of secondary phosphine oxides to propargyl alcohols leading to the formation of 1,3-butadienes [485],... 

Nickel catalyzed addition of diphenyldichalcogenides (S and Se) on alkynes have been shown to produce 1,4-dichalcogenodienes 215. The formation of complex 214 can account for the stereoselectivity of the process (Scheme 84) [178]. 

Ananikov VP, Zalesskiy SS, Orlev NV, Beletskaya IP (2006) Nickel-catalyzed addition of benzenethiol to alkynes formation of carbon-sulfur and carbon-carbon bonds. Russ Chem Bull Int Ed 55 2109-2133... 

According to the detailed results [7] on the nickel-catalyzed addition of //-phosphonate to terminal alkynes [8], the reaction of HP(0)(0Me)2 with 1-octyne run in ethanol at room temperature gives the linear isomer as major product (Scheme 2). As is anticipated in view of the influence of acidic additives found with palladium catalysts [9], the same reaction run with diphenylphosphinic acid added as an additive reverses the regioselectivity (branched/linear = 92/8). HP(0) Ph(OEt) and HP(0)Ph2 behave similarly. 

Nickel-catalyzed addition of //-phosphonates with alkynes was also revisited using mainly HP(0)(0 Pr)2 and 1-heptyne [12]. Among the catalyst systems tested, the combination of [Ni(acac)2] (Ni(acac)2 can be in situ reduced to Ni(0) see [13]) and dppe appears best performing and affords branched products as major products (Scheme 4), at >100°C depending on the structures of //-phosphonate and alkyne. Use of monophosphines and other diphosphines did not display catalytic activity. 

Due to the successful development of the catalyzed hydrophosphorylation, its extension to functionalized alkynes is becoming of interest. Nickel-catalyzed addition of //-phosphonate (and also //-phosphinate and sec-phosphine oxide) to propargyhc alcohols is an interesting example, as discussed later (Sect. 4). 

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