Nickel catalysts cycloaddition reactions

A catalytic asymmetric cycloaddition reaction between norbomadiene and methylenecyclopropane can also be achieved in the presence of a [Ni(cod)2]-(—)-benzylmethylphenylphosphine catalyst to give the cycloadduct (72) in an optically active form. This reaction may proceed via a metallocyclopentane intermediate. The reactions of methylenecyclopropane with [Ni(cod)2l-phosphine systems do not appear to involve cleavage of the three-membered ring. However, the bis(acrylonitrile)nickel-catalysed cycloaddition reaction of methylenecyclopropane with methyl acrylate, which yields 3-methoxy-carbonylmethylenecyclopentane (73), does involve C—C bond cleavage. Reaction with the deuterium-substituted compound CHD=CDC02Me gives the cyclopentane derivative (74). An intermediate of the type (75) may be involved in this reaction. 

An example that illustrates the influence of the nickel catalyst on the reaction yield is the cycloaddition between tricyclo [5.3.1.0" ]-undeca-2,5-diene(90) and dimethylacetylenedicarboxylate (Equation 3.31). Whereas a thermal process afforded cycloadduct 91 in an unsatisfactory yield (22 %), the catalyzed process... 

The NHCs have been used as ligands of different metal catalysts (i.e. copper, nickel, gold, cobalt, palladium, rhodium) in a wide range of cycloaddition reactions such as [4-1-2] (see Section 5.6), [3h-2], [2h-2h-2] and others. These NHC-metal catalysts have allowed reactions to occur at lower temperature and pressure. Furthermore, some NHC-TM catalysts even promote previously unknown reactions. One of the most popular reactions to generate 1,2,3-triazoles is the 1,3-dipolar Huisgen cycloaddition (reaction between azides and alkynes) [8]. Lately, this [3h-2] cycloaddition reaction has been aided by different [Cu(NHC)JX complexes [9]. The reactions between electron-rich, electron-poor and/or hindered alkynes 16 and azides 17 in the presence of low NHC-copper 18-20 loadings (in some cases even ppm amounts were used) afforded the 1,2,3-triazoles 21 regioselectively (Scheme 5.5 Table 5.2). 

In the presence of nickel(0), tethered diene-VCPs react to produce eight- and five-membered ring products (Scheme 2). Palladium(O) and cobalt(m) were also tried but produced only decomposition products. However, in the presence of Wilkinson s catalyst (RhCl(PPh3)3), tethered diene-VCP 1 was cleanly converted to triene 4 in 91% yield. Although the desired cycloaddition reaction was not obtained, the cleavage of the cyclopropane ring was encouraging.22... 

The [4+ 4]-cycloaddition reaction of tethered bis-dienes has been used by Wender and co-workers in total synthesis as exemplified in syntheses of ( )-salsolene oxide and (-l-)-asteriscanolide (Scheme 28). In the synthesis of ( )-salsolene oxide, a nickel(0)-catalyst cleanly effects the cycloaddition of the two conjugated dienes in compound 93 to afford the bicyclo[5.3.1]undecadiene in a good yield and with moderate selectivity.99 The first synthesis of (-l-)-asteriscanolide was accomplished in only 13 steps. The key [4+ 4]-cycloaddition reaction efficiently set the requisite eight-membered ring of (-l-)-asteriscanolide in good yield and with excellent diastereoselectivity.100 The diastereoselective [4 + 4]-cycloaddition has also been applied to the synthesis of the core ring system found in several sesterterpenes such as the ophiobolins (Scheme 28).101... 

Transition metal-catalyzed [4+ 2]-cycloadditions ofdiene-allenes 247 can lead to different results. With a nickel catalyst Wender et al. isolated the anellated system of two six-membered rings 248 with a rhodium catalyst the anellation of a five- and a six-membered ring 249 was possible (Scheme 15.78) [149]. Both transformations proceed readily at low temperatures whereas the uncatalyzed thermal reaction requires 185 °C. Even an anellation of a six- and a seven-membered ring was achieved. 

Formally, although these cyclooligomerizations can be considered as cycloaddition reactions, they are known not to occur through a direct cycloaddition process. In the best understood nickel-catalyzed reaction the dimer 12 was shown to be the key intermediate in cyclization.46,59 60 Acetylene readily undergoes cyclooligomerization in the presence of metal catalysts to form benzene and cyclooctatetraene [Eq. (13. 15)] as well as higher homologs ... 

The use of Diels-Alder-type cycloaddition reactions is the most intensively investigated cycloaddition approach to the design of ladder polymers in a concerted process. Another methodology was published by Tsuda and coworkers [52, 53, 54]. They developed a nickel (0)-catalyzed [2 + 2 -l- 2] cycloaddition copolymerization of cyclic diynes 38 with heterocumulenes (like carbon dioxide or isocyanates 39). The soluble ladder-type products - poly(2-pyrone)s and poly(2-pyridone)s 40 - possess molecular weights M of up to 60000, corresponding to a Dp > 200. Unfortunately, the products formed were contaminated by nickel salts originating from the catalyst used Ni(COD)2. 

Reetz MT, Breinbauer R, Wedemann P, Binger P (1998) Nanostructured nickel-clusters as catalysts in [3+2] cycloaddition reactions. Tetrahedron 54 1233... 

Yield improvements and changes in selectivity were observed by using nickel, cobalt or manganese catalysts in this cycloaddition. Noteworthy is the formation of a new isomer, 8-ethylidenetetracyclo[4.3.0.0 . 0 ]nonane, shown to be the primary product (8%) of the homo-Diels-Alder reaction when a nickel catalyst was used." ... 

The result of the reaction with MCP and dimethyl bicyclo[2.2.1]hept-2-ene-2,3-dicarboxylate vide supra) is in contrast to the outcome of most nickel-catalyzed [3 + 2] cycloadditions in the absence of phosphanes ( naked nickel catalysts) which employ unsaturated esters as cosubstrates. Normally, products arising from formal proximal cleavage of the three-membcred ring are formed in these cases. All of these reactions proceed readily at slightly above room temperature (20 40°C) and are highly regio- and stereoselective. 

With /1-substituted unsaturated esters, e.g. methyl ( )-crotonate or dimethyl maleate, the stereochemistry at the alkene group is predominantly retained in the products, i.e. methyl rra7i -2-mcthyl-3-methylenecyclopentanecarboxylate (3) and dimethyl 3-methylenecyclopen-tane-1,2-dicarboxylate (4), when phosphane-free nickel catalysts are employed at temperatures slightly above room temperature. When equimolar amounts of MCP and dimethyl maleate are used, approximately equal amounts of homocyclodimers of MCP and [3 + 2] cycloadducts arc obtained, even if the MCP is added dropwise to the catalyst solution in dimethyl maleate, indicating that the cycloaddition is a relatively slow reaction. When the maleate/MCP substrate ratio is increased to 3 1, the yield of the codimers 4 is raised to 78%.Dialkyl fumarates and maleic anhydride do not undergo cycloaddition under these conditions. 

Compared with the naked nickel reactions, reactions with phosphane-modified nickel catalysts require higher temperatures (80-100 C) in order to proceed at a reasonable rate and usually exhibit a decreased stereoselectivity. Despite these obvious drawbacks, such catalyst systems are advantageous in the case of highly electron-deficient alkenes, such as ( )-but-2-enal. ° or dialkyl fumarates, which can be readily employed as cycloaddition substrates only with modified nickel catalysts (vide supra). 

Benzylidenetricyclo[5.2.1.0 ]decane (5) is the major poduct from the [3 + 2] cycloaddition of either benzylidenecyclopropane (3) or l-methylene-2-phenylcyclopropane (4) and norbornene in both nickel(O)- and palladium(0)-catalyzed reactions. Ring-substituted products, anti- and 5yn-4-methylene-3-phenyltricyclo[5.2.1.0 ]decane (6A) and (6B), respectively, are formed in minor amounts. Whereas under the influence of the palladium(O) catalyst the reaction requires 70-120 °C to proceed at a reasonable rate, nickel(O) as a more active catalyst induces the reaction readily at 40 °C. Combined yields are, at least with the palladium(O) catalysts, close to 100% in all cases. 

The cycloaddition reaction of 2,3-diphenylcyclopropenone with ketenes and tetracarbonyl-nickel(O) catalyst gave cyclopent-3-ene-l,2-diones 20. ... 

Cycloaddition.2 In the presence of this nickel catalyst, methylenecyclo-propanes undergo an unusual cycloaddition across carbon-carbon double bonds. Thus methylenecyclopropane (1) when heated in a sealed tube (60°, 48 hrs.) with excess methyl acrylate in the presence of bis(acrylonitrile)nickel(0) gives the 1 1 adduct, methyl 3-methylenecyclopentanecarboxylate (2), in 82% yield. Methyl vinyl ketone or acrylonitrile is also a suitable substrate. The reaction provides a useful synthesis of methylenecyclopentane derivatives. 

Low-valent transition metal catalyzed versions of [2 + 2] cycloadditions. especially with nickel catalysts, were recognized early as useful alternatives to thermal and photochemical methods12-15. The observation of transition metal catalysis, active in [2 + 2]-cycloaddition reactions, originally caused considerable discussion of the mechanism as an inversion of symmetry rules, effected by the transition metal, may be assumed. Thus, it was suggested that, in the presence of the metal catalyst, a forbidden reaction becomes allowed 16,17. This interpretation, however, could not be verified for the overall process, since experimental investigations revealed a stepwise mechanism with metallacycle intermediates18-23. 

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