Nickel catalysis alkynes

Despite the excess of alkyne used, the transfer of only one vinylic group was observed. A more general approach of this method involves the reaction of (Z,Z)- and (f ,fi)-divinylic tellurides with alkynes under nickel catalysis, to give (Z)- and ( )-enynes with complete retention of configuration."... 

Despite the tremendous range of thermal and Lewis acid-promoted [4+2] cycloadditions that can be routinely accomplished, the nickel-catalyzed counterpart to these reactions provides unique opportunities for efficiency and selectivity. The [4+2] cycloaddition of 1,3-dienes with alkynes is a subclass of reactions that enjoys particular benefits from nickel catalysis. In illustrations involving assembly of the all-carbon cyclohexadiene units, reports from Wender described the efficient intramolecular cycloaddition of 1,3-dienes with alkynes (Scheme 3-20). Notably, the corresponding thermal processes either failed to proceed or required harsher conditions, providing substantially lower yields than the corresponding nickel-catalyzed processes. The stereochemistry of the diene is conserved in the cycloadditions, as a comparison in Scheme 3-20 of E,E- and ,Z-dienes illustrates. 

Coupling reactions of aromatic, heteroaromatic, and vinylic substrates with alkynes via sp C—H bond cleavage under rhodium, iridium, ruthenium, palladium, or nickel catalysis to produce a wide range of cyclic compounds have been described in this chapter. These annulation reactions provide powerful methods for constructing a variety of -rr-conjugated molecules containing fused aromatic and heteroaromatic nuclei from simple, readily available substrates. Extensive efforts will continue to be made to extend the scope of starting materials for this catalysis. 

Although the titanium-based methods are typically stoichiometric, catalytic turnover was achieved in one isolated example with trialkoxysilane reducing agents with titanocene catalysts (Scheme 28) [74], This example (as part of a broader study of enal cyclizations [74,75]) was indeed the first process to demonstrate catalysis in a silane-based aldehyde/alkyne reductive coupling and provided important guidance in the development of the nickel-catalyzed processes that are generally more tolerant of functionality and broader in scope. 

Trost reported the synthesis of 1,4-dienes with ruthenium catalysis through regioselective carbometallation of alkynes with alkenes.51 Di- and trisubstituted olefins can also be obtained with arylboronic acids through an intermolecular process under rhodium,30 52 55 nickel,56 and palladium catalysis.57 Recently, Larock has reported an efficient palladium-catalyzed route for the preparation of tetrasubstituted olefins.58,59... 

Nickel(O) catalysis has been utilized for a three-component coupling between an allylic electrophile, and alkyne, and AlMe3 or ZnMe2. This reaction takes place though the insertion of a 7r-nickel(ll) intermediate into the alkyne,... 

The same type of bis-functionalization has been reported for the palladium-catalyzed borylstannylative carbocy-cyclization of 1,6-, 1,5-, 1,7-diynes, bis-propargylamine, and ether.377 It should be noted that even 1,2-dialkylidene cyclobutane can be obtained in reasonable yield. Ito has proposed the related silaborative reaction involving nickel(O) catalysis.378 This reaction has been performed in an intra- and intermolecular fashion. The intramolecular reaction allows the formation of cyclic dienes and the intermolecular process proceeds through a dimerization of alkynes to give acyclic dienes. 

Related co-cyclotrimerizations of two alkyne molecules with limited isocyanates have also been achieved using cobalt and nickel catalysts. With respect to intramolecular versions, two examples of the cobalt(I)-catalyzed cycloaddition of a,m-diynes with isocyanates have been reported to afford bicyclic pyri-dones only in low yields, although 2,3-dihydro-5(lff)-indolizinones were successfully obtained from isocyanatoalkynes and several silylalkynes with the same cobalt catalysis [19]. On the other hand, the ruthenium catalysis using Cp RuCl(cod) as a precatalyst effectively catalyzed the cycloaddition of 1,6-diynes 21 with 4 equiv. of isocyanates in refluxing 1,2-dichloroethane to afford bicyclic pyridones 25 in 58-93% yield (Eq. 12) [20]. In this case,both aryl and aliphatic isocyanates can be widely employed. 

Metal complex chemistry, homogeneous catalysis and phosphane chemistry have always been strongly connected, since phosphanes constitute one of the most important families of ligands. The catalytic addition of P(III)-H or P(IV)-H to unsaturated compounds (alkene, alkyne) offers an access to new phosphines with a good control of the regio- and stereoselectivity [98]. Hydrophosphination of terminal nonfunctional alkynes has already been reported with lanthanides [99, 100], or palladium and nickel catalysts [101]. Ruthenium catalysts have made possible the hydrophosphination of functional alkynes, thereby opening the way to the direct synthesis of bidentate ligands (Scheme 8.35) [102]. 

Alkynes can also serve as substrates in [3 -I- 2] cycloadditions to MCP, as exemplified by the reaction of but-2-yne under nickel/phosphite catalysis to provide l,2-dimethyl-4-methylene-cyclopent-l-ene (2). 2 However, alkyne oligomerization, specifically cyclotrimerization, cannot be avoided with alkyl-substituted alkynes. When alkynes with electron-withdrawing substituents are employed, cyclotrimerization becomes the exclusive reaction. 

Similar findings have been reported by Ishikawa and coworkers. Using the disilacyclobutene (100) as the key reactant, they have found that disilacyclopentane and -ene products, e.g., (102)-(107), can be obtained using non-enolizable ketones <930M87>, alkenes, dienes <930M4987, 950mii4>, or alkynes <95JOM(499)35> with nickel or platinum catalysis—presumably via metal insertion intermediates such as (101) ( heme 12). 

Using catalysis by palladium systems, allylic halides show little tendency to add. However, with nickel(O) catalysts [e.g., Ni(cod)2] allylic halides add to norbornene. in contrast to vinyl and aryl halides9. The palladium system also catalyzes the coaddition of alkynes and benzylic halides to strained bicyclic alkenes10- u. Thus, addition of methyl 2-[3-(chloromethyl)phenoxy]acetate and optically pure (S)-l-octyn-3-ol to norbornene, norbornadiene or 7-oxanorbornene 4 leads to diastereomeric adducts 5, used as precursors of interphenylene prostaglandin endoperoxides, in 34-58% yield. No diastereomeric ratios were reported. 

Many examples of alkene and alkyne insertion into metal-carbon bonds can also be found in the section on homogeneous catalysis. Other recent examples include the insertion of conjugated dienes into palladium-allyl bonds, olefin arylation in the presence of palladium acetate, and the reaction of ethylene with arylmagnesium halides in the presence of nickel chloride. Reaction of isocyanates with nickel-ethynyl compounds... 

---