Dimerization of norbomadienes

Codimerization of butadiene with dicyclopentadiene (example 8, Table II) was shown to proceed via a crotyl-nickel complex (62). Ring contraction of cyclooctadiene (example 10, Table II) appears to be a hydride promoted reaction. The hydride-promoted dimerization of norbomadiene to -toly 1 norbornene (example 9, Table II) appears to be quite different from dimerization via a metallacycle (see Table I, example 16). 

Intermediate metallacyclopentanes are also implicated in transition metal-catalyzed alkene cycloadditions to form cyclobutanes and the corresponding cycloreversions, e.g. dimerization of norbomadiene (73JA597) and rearrangements of cubane and other cyclo-butanoid hydrocarbons (78JA2573). 

Mays and co-workers (33) found that [FeCo3(CO)12] and FeCo3H(CO)12 catalyze the dimerization of norbomadiene, Eq. (99). The results were highly dependent on the solvent and the cocatalysts employed. FeCo3H(CO)12 was more effective than [FeCo3(CO)12], but the nature of the actual catalytic species was not determined. 

Norbomadiene dimerization to Bisnor-S (2,123-124 3,89-90.)1 The dimerization of norbomadiene to Bisnor-S with this catalyst in conjunction with boron trifluoride etherate can be effected in 80% yield if the initial temperature is controlled carefully (exothermic reaction). 

The process is catalyzed by a number of cobalt and rhodium clusters 361). Anionic clusters such as [FeCo3(CO),2] and [Coj(CO),5] show greater catalytic activity than would be expected from neutral clusters of the same size 361). Other mixed-metal clusters, such as Zo2C04(CO),5 362) and Pt3Co2(CO)9(PPhj)j 363), have also been reported to be active for the stereospecific dimerization of norbomadiene to give 81. In the presence of BF3 Et20, Pt3Co2(CO)9(PPhj)3 converts norbomadiene into 81 with 100% yield and 100% selectivity (20 °C, 30 min, CT 31). 

Table I). Codimerization of this dimer with norbomadiene also gives preferentially one stereoisomer, the exo,trans,exo,trans,exo isomer (30). 

Booth et al. (M3) carried out the reaction of [Mn(CH3)(CO)j] with cyclo-pentadiene and found the reaction to be so slow that dimerization of cyclopentadiene occurred before reaction with [Mn(CH3)(CO)5] [Eq. (40)]. The reaction of [Mn(R)(CO)j] (R = CH3, Ph) with dicyclopentadiene directly, however, also gave a 1 2 adduct [Eq. (41)]. The reaction of [Mn(CH3)(CO)5] with norbomadiene, which gave a mixture of the 1 1 and 1 2 adducts, was also reported in this study. Other studies with different alkenes and alkynes gave the same type of products (M4,M5). 

An excess of norbomadiene (5 mL) was added to a solution of 7V,7V-diisopropyldithiatriazin-5-amine dimer Id (0.30 g, 1.4 mmol) in Et20 (30 mL) at — 20 °C. After 2 h at 23 X solvent and excess of norbomadiene were removed under vacuum to give a sticky yellow residue. Recrystallization (hexane) at — 20 X gave pale-yellow crystals of compound 4c yield 0.25 g (57%) mp 145 °C. 

A slurry of 5-phenyldithiatria7ine dimer le (0.45 g, 1.15 mmol) in MeCN (5 mL) was reacted with an excess of norbomadiene (5 mL) and the resulting mixture stirred for 16 h, The resulting precipitate of the crude adduct was recrystallized (MeCN) to give colorless plates of compound 4d yield 0.42 g (63%) mp 179 — 180 °C. 

There are only a few cases of an intermolecular reaction of a 7r-allylpalladium complex with an alkene. The carbopalladation of norbomadiene with a stoichiometric amount of a TT-allylpalladium complex to yield an allyl-substituted a--norbomenylpalladium species has been reported In the context of mechanistic studies of Pd-catalyzed alkene dimerization, the insertion of ethylene into a cationic 7r-allylpalladium complex was also reported as a stoichiometric reaction in 1996 (Scheme... 

The 1 1 complex derived from phenyltungsten trichloride and aluminium trichloride is an effective catalyst for diene-cyclobutane metathetical interconversions. Thus, the tetracyclic compounds (291) and (292) were respectively isomerized to the dienes (293) and (294). Rather more surprising was the virtually quantitative formation of the cyclobutanoid compound (296) from (295). Reaction of norbomadiene with 2,2 -bipyridyl(cyclo-octa-l,5-diene)nickel at 25°C yielded the exo-trans,endo-metal o-carbocyclic (297) which, on treatment with an activated olefin (e.g. maleic anhydride), afforded the cyclo-dimer (298 predominantly exo-trans,endo) in good yield by displacement of the hydrocarbon moiety. Catalytic conversions can also be achieved. 

When a solution of norbomadiene and methylenecyclopropane in benzene in the presence of Ni(COD)2 and PhjP is allowed to stand for 24h at room temperature, the dimeric product containing cydobutaine moiety is obtained in 86% yield [114]. 

Roth, Schilling and coworkers [47-54] have investigated the nuclear spin polarization behavior of cation-radicals of numerous strained hydrocarbon systems produced by PET to strong electron acceptors such as chloranil, anthraquinone and cyanoaromaties. These systems include cyclopentadiene dimers, methyl-enebicyclo[2.2.0]hexenes [48], bicyclo[1.1.0]butanes [49], hexamethyl (Dewar benzene) [50], norbomadiene [53], quadricyclene [53], and 1,2-diphenylcyclopropanes [54]. 

Pauson and Khand discovered the very important class of alkyne/alkene/CO cyclization catalytic reactions catalyzed, once again, by Co2(CO)g see Pauson-Khand Reaction). This reaction produces a, /3-unsaturated cyclopentanones (equation 23). With unstrained alkenes the reaction works best in a stoichiometric setting, but with strained alkenes like norbomadiene the reaction can be made catalytic. These reactions have been fairly extensively studied, and the reaction proceeds through an alkyne-bridged Co2(CO)6 dimer species. Unsymmetrical alkynes lead to mixtures of the various substituted a, /3-unsaturated cyclopentanone products. 

Hammond and collaborators as part of their extensive studies on photosensitized reactions. Examples include (a) cis-trans isomerization of olefins sensitized by biacetyl 42,64,65,176 2,3-pentanedione 64>65>, benzil 64,65,89)> a. and /3-naphil 64>, and phenanthrenequinone 30-65> (b) diene and anthracene dimerizations sensitized by biacetyl 9>45>94>, 2,3-pentanedione 4,162)j camphorquinone 04>, benzil 84,162) and / -naphthil 94>, and (c) the quadricyclene-norbomadiene interconversion sensitized 66> by benzil. 

The reaction of the /V,/V-diethyl-l, 3-dichlorodithiatriazin-5-amine dimer lc with norbomadiene in the presence of triphenylstilbane yielded 24% of compound 4b.7... 

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