Cycloadditions palladium/nickel-catalyzed

Nickel catalyzed [3 + 2] cycloadditions of methylenecyclo-propane and 2,2-dimethylmethylenecyclopropane with (4) afford 3-methylenecyclopentane derivatives with extremely high TT-face selectivities (91% and 98% de respectively) five alternative auxiliaries were found to be less effective. - Palladium catalyzed [3 + 2] cycloaddition of 2-(TMS-methyl)-3-acetoxy-l-propene with an N-enoylsultam, however, proceeds with disap-... 

Compared with the Diels-Alder reaction, the [2+2+2]-cycloaddition is potentially more powerful since the number of new bonds as well as chirality centers that are formed is higher. Unfortunately, the reaction seems to be entropically or kinetically unfavorable. This disadvantage can, however, be overcome by the use of transition metal catalysts (templates). Among the most successful examples of this reaction type, the nickel(II) catalyzed Reppe reactions 96), the cobalt(I) catalyzed cocyclizations of a,to-diynes with alkynes 97), the cobalt(I) catalyzed pyridine synthesis 985 and last but not least the palladium(0) catalyzed cyclotrimerizations of 3,3-dialkylcyclopropenes to frans-cr-tris-homobenzenes must be mentioned. The latter has been known for ten years 99>. 

In nickel-catalyzed reactions, the cyclopentane with the electron-withdrawing group in the 3-position (relative to the exo-methylene group) is formed almost exclusively. This is in contrast to the palladium-catalyzed, formal [3-1-2] cycloaddition employing 2-(trimethylsilylme-thyl)prop-3-enyl acetate as precursor, which presumably follows a mechanistically different, ionic pathway. In palladium-catalyzed MCP reactions of that type, the observed selectivity is markedly dependent on the specific reactants. 

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. 

Tetracarbonylnickel and other nickel(O) compounds, as well as palladium complexes, catalyze the [2 + 2 + 1] cycloaddition of allylic systems with alkenes or alkynes and carbon monoxide to form cyclopentanones or cyclopentenones. This reaction type resembles stoichiometric zirconium- and cobalt-mediated [2 + 2 + 1] cycloadditions (vide supra), mechanistically, however, it proceeds via transition metal 7r-allyl complexes. 

A wide range of alkyl/aryl 4H-thiochromen-4-ones are readily available from the nickel-catalyzed decarbonylative cycloaddition of thioisatins with alkynes in toluene at 50 °C (14OL5660).The reaction of 3-aryl-1-substituted prop-2-en-l-ones with NaSH in DMF at low temperature (—20°C) gave access to 2-aryl-4H-thiochromen-4-one-type compounds (14H(89)495). A palladium(II)-catalyzed dehydrogenative cyclization of aryl benzyl sulfoxides and iodobenzene-produced dibenzothiopyran S-oxides in moderate-to-good yields (140L4574). 

Palladium-catalyzed intramolecular [3+2] cycloadditions starting from alkenylidenecyclopropanes have been reported by Mascarenas et al. [44]. For related nickel-catalyzed reactions, the intermediacy of trimethylenemethane complexes has not been invoked [45]. 

Notably, the nickel-catalyzed decarbonylative cycloaddition affords a regioisomer opposite to that formed in the palladium-catalyzed Larock heteroannulation [21], For example, the nickel-catalyzed reaction of anthranilic acid derivatives 39 with l-trimethylsilyl-2-phenylacetylene (43) affords indole 44 with phenyl substituents at the 2-position [Scheme 12.18(a)], whereas the palladium-catalyzed reaction... 

A tremendous amount of work concerning metal-induced cycloadditions of methylenecyclopropane with olefins and alkynes has been done in recent years since the first reported nickel(0) catalyzed 3+2 cycloaddition of methylenecyclopropanes with electron-poor olefins (equation 352)415 and the analogous palladium(O) codimerization (equation... 

Metal-n-allyl complexes are important in a number of stereoselective catalytic reactions and are therefore attractive for computational chemists (see also Chapter 13, Section 13.2). An empirical force field study based on the MM2 parameterization scheme aimed at predicting stereoselective nickel(0)-catalyzed cycloadditions was recently conducted 56. As in a similar study 57, where a force field for the structure optimization of palladium-allyl systems was developed, dummy atoms were needed to define the structural model. Based on the assumptions required to model a catalytic process, the results obtained have to be interpreted with caution. 

The complexes [Ni(acrylonitrile)2] and [Ni(COD)2] catalyze [3 + 2] cycloadditions of (26) with electron deficient l,2 isubstituted alkenes to afford 2,3- or 3,4-disubstituted methylenecyclopentanes such as (32) and (33). Similar reactions have been reported by use of tertiary phosphine complexes of nickel(0) and palladium(0) (equation 13 and Table 1). The reaction proceeds regioselectively to give (32) or (33) depending on both the alkene stmcture and catalytic system. Reactions catalyzed by phos-phine-palladium(0) complexes afford only products of the type (32), via selective cleavage of the C(2)— C(3)bondof(26). 

Nickel(0)-catalyzed [3 + 2] cycloadditions of methylenecyclopropanes with A(-substituted maleimides (56 equation 22) lead almost exclusively to 5-alkylidenehexahydro-l//-cyclopenta[c]pynolo-l,3-diones (57) and (58 equation 23). A similar reaction occurs in the presence of a palladium(O) catalyst, but with lower selectivity. Unsubstituted maleimide and maleic anhydride do not undergo this cycloaddition. Ozonolysis of (57) and (58) into the corresponding ketone derivatives (62-78% yield) followed by reduction of both carbonyl groups gives l//-cyclopenta[c]pynoles, which are of interest with regard to their pharmacological activity (98% yield). ... 

The asymmetric 1,3-dipolar cycloaddition of nitrones to 3-(( )-2-butenoyl)-2-oxazoli-dinone [214] is catalyzed by nickel(II) [215] and palladium(II) [216] complexes (Sch. 66). The resulting isoxazolidines are of interest because they are readily converted into y-amino alcohols, precursors to alkaloids and /3-lactam antibiotics. 

Instead of a second or third alkyne, an alkene C=C double bond may be incorporated into the cyclotrimerization reaction. Iron [65], rhodium [66], nickel [67], palladium [68], or cobalt [69] catalysts have been used to form cyclohexa-dienes. However, the preparative use of this catalytic co-cyclization is disturbed by consecutive side reactions of the resulting dienes such as cycloaddition or dehydrogenation. Itoh, Ibers and co-workers [70] have reported the straight palladium-catalyzed co-cyclization reaction of C2(C02Me)2 and norbomene (eq. (24)). 

In some palladium-catalyzed cyclizations of enynes a [2 + 2] cycloaddition with subsequent metathesis-like rearrangement leads to other cyclic products50,51. The transition metal catalyzed Alder ene type cyclization reactions can also be applied to diynes52 and to enal-lenes53-55. The latter reaction is best performed using a polystyrene-supported nickel(II)/ chromium(II) catalyst. With the appropriate choice of substituents complete stereoselectivity can be achieved using this method55. 

Nickel- and Palladium-Catalyzed Stereoselective [3 + 2 Cycloaddition with IVlethylenecyclopropanes as Trimethylenemethane Precursors... 

Cyclopropenes and mcthylcnccyclopropanes serve as multifunctional reagents in transition metal catalyzed reactions22. Methylenecyclopropanes, via C-C bond cleavage, are also used as trimethylenemethane precursors in transition metal catalyzed [3 + 2] cycloadditions for selective five-membered-ring formation. Low-valent nickel and palladium complexes are used as catalysts. This method has been extensively reviewed 22 and stereoselective applications are fully described in Section D.1.6.1.2.3. 

In early reports on nickel(0)-catalyzed (3 + 2] cycloaddition reactions of methylenecyclo-propane with alkenes, orientation and stereochemistry was investigated37. Additionally, palladium-catalyzed versions of this formal [2intramolecular mode of a palladium-catalyzed version, an additional chelation effect can be used for control of regio- and stereochemistry to yield the thermodynamically less favored frtwv-fused bicyclo[3.3.0] octanes 39. 

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