Cyclodimerization of 1,3-diene

Polymer-based phosphine nickel carbonyl Cyclodimerization of 1,3-dienes... 

The use of zeolites is particularly advantageous for self-Diels-Alder reactions of gaseous dienes because it reduces the polymerization of the reactant. An example is the cyclodimerization of 1,3-butadiene to 4-vinylcyclohexene [20a] carried out at 250 °C with satisfactory conversion when non-acidic zeolites, such as large-pore zeolites Na-ZSM-20, Na- S and Na-Y, are used. 

In a series of papers published in the 1960s by Schmidt and coworkers, there is no description of any successful and stereospecific reaction of 1,3-diene compounds, e.g., topochemical polymerization, other than cyclodimerization. They... 

In 1981, this cation radical Diels-Alder cyclodimerization of 1,3-cyclohexadiene was shown to be more cleanly (only 1 % of the cyclobutane dimers is produced), conveniently (in a synthetic organic context), and efficiently (70 % yield) carried out by chemical ionization of the diene, using 3+ (Scheme 15) [39]. 

However, the cyclodimerization of 1,3-cyclohexadiene and also the addition of the cis,cis isomer of 2,4-hexadiene to 1,3-cyclohexadiene are only modestly stereoselective. The addition of cis,rra i-2,4-hexadiene to 1,3-cyclohexadiene is highly stereoselective for the addition to the lra s-propenyl group, but only modestly stereoselective for the addition to the cw-propenyl group. Further, the addition of a dienophile having a pendant, unsubstituted vinyl double bond to this diene is also highly endo stereoselective. The installation of a cis group at the terminus of the dienophilic moiety consistently appears to reduce the endo stereoselectivity to a more modest level. It has been proposed that the cis substituent attenuates the secondary interaction involving the endo double bond in the transition state for cycloaddition [47, 48]. The effect has been termed the cfs-propenyl effect . The addition of the ira j-anethole cation radical to both 1,3-cyclohexadiene and 1,3-cyclopentadiene is, however, only moderately diastereospecific (ca 3 1) [49]. 

Of further interest is the observation that the same reaction is not observed at all under PET conditions, which should reliably furnish the same diene cation radical [50]. Further, the normally efficient cation radical cyclodimerization of 1,3-cyclohexadiene is completely inhibited in the presence of the hindered diene, so that... 

An intriguing competition arises in the context of cation radical cycloadditions (as in the context of Diels-Alder cycloadditions) which involve at least one conjugated diene component. Since both cyclobutanation and Diels-Alder addition are extremely facile reactions on the cation radical potential energy surface, it would not be surprising to find a mixture of cyclobutane (CB) and Diels-Alder (DA) addition to the diene component in such cases. Even in the cyclodimerization of 1,3-cyclohexadiene, syn and anti cyclobutadimers are observed as 1 % of the total dimeric product. Incidentally, the DA dimers have been shown not to arise indirectly via the CB dimers in this case [58]. The cross addition of tw 5-anethole to 1,3-cyclohexadiene also proceeds directly and essentially exclusively to the Diels-Alder adducts [endo > exo). Similarly, additions to 1,3-cyclopentadiene yield essentially only Diels-Alder adducts. However, additions to acyclic dienes, which typically exist predominantly in the s-trans conformation which is inherently unsuitable for Diels Alder cycloaddition, can yield either exclusively CB adducts, a mixture of CB and DA adducts or essentially exclusively DA adducts (Scheme 26) [59]. 

The first catalytic cyclodimerization of 1,3-butadiene (BD) to 1,5-cycloocta-diene using modified Reppe catalysts was reported by Reed in 1954 [4], and only two years later Wilke reported on the titanium-catalyzed synthesis of cyclo-dodecatrienes from BD [5]. It remained for Wilke and his co-workers to show the tremendous versatility and scope of the nickel-catalyzed cyclooligomerizations of... 

Fe compounds have received much less significant attention than Ni or Co compounds as the diene polymerization catalyst. FeEt2(bpy)2 catalyzes cyclodimerization of 1,3-butadiene [79] and polymerization of vinyl monomers such as acyclic ester [80]. Recently, FeEt2(bpy)2/MAO was found to show high catalytic activity toward 1,2-polymerization of 1,3-butadiene and 3,4-polymerization of isoprene at -40 to +25 °C (Eq. 14) [81]. The crystalline polybutadiene prepared below 0 °C is composed of... 

Additional experiments were also carried out with complex 133 which results from the substitution of the COD ligand in 73 by a 1,4-diaza-l,3-diene (DAD) [48], The catalytic activity of 133 in the cyclodimerization of 1,3-butadiene was compared to that of its carbon counterpart the [Fe(r/6-toluene)(DAD)] complex. In this case, the toluene complex proved to be 10 times more efficient and yielded better TON than the phosphinine-based complex for the formation of COD (1,5-cyclooctadiene) and VCH (vinylcyclohexene). This lack of activity was ascribed to the stronger affinity of phosphinine ligands towards Fe(0) thus limiting the generation of the 12 VE [Fe(DAD)] complex which is the genuine catalytic active species (Scheme 27). 

Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

The reaction mechanism of nickel-catalyzed cyclodimerization has been investigated.10 The dimerization of buta-1,3-dienes is also possible with palladium salts.11... 

For example, the dinitrosyliron(O) complex can be formed cathodically. This complex is able to catalyze the cyclodimerization of conjugated dienes (Scheme 8) 259,260) in case of 1,3-butadiene, 20000 turnovers are obtained per hour with... 

Cyclooligomerization. Ever since the first cyclodimerization reaction of 1,3-butadiene to yield 1,5-cycloctadiene catalyzed by a so-called Reppe catalyst was reported45 [Eq. (13.12)], cyclooligomerization of conjugated dienes has been intensively studied ... 

Homogeneous nickel complexes proved to be versatile catalysts in dimerization and trimerization of dienes to yield different oligomeric products.46-55 Depending on the actual catalyst structure, nickel catalyzes the dimerization of 1,3-butadiene to yield isomeric octatrienes, and the cyclodimerization and cyclotrimerization to give 1,5-cyclooctadiene and all-trans-l,5,9-cyclododecatriene, respectively46 56 [Eq. (13.13)]. Ziegler-type complexes may be used to form cis,trans,trans-1,5,9-cyclododecatriene37,57 58 [Eq. (13.14)], which is an industrial intermediate ... 

For H-acid catalysis stereospecifity is lowered and appears to be the same as in the reactions initiated with trifluroacetic acid instead of the ammoniumyl salt. For the cation-radical mechanism the sterically hindered base 2,6-bis(tert-butyl)pyridine does not inhibit the cyclization triarylamine retards this reaction photosensibilized one-electron oxidation of a diene leads to the same products, which are formed in the presence of the ammoniumyl salt. As shown, in the majority of cases only the cation radical chain mechanism of the diene-diene cyclization is feasible (Bauld, Bellville, Harirchian 1987). Meanwhile, cyclodimerizations of 2,4-dimethylpenta-1,3-diene (Gassman Singleton 1984) and 1,4-dimethylcyclohexa-1,3- or -1,4-diene (Davies et al. 1985) proceed through both mechanisms. 

The cyclooligomerization reaction is not confined to BD as the monomer. Activated or monosubstituted 1,3-dienes also react, but reaction rates are usually slow, and selectivity and turnover numbers (TONs) are low. Cyclotrimerization and cyclodimerization of substituted 1,3-dienes - either alone or in admixture with BD - give numerous isomers of substituted CDT, COD, VCH and divinyl-cyclobutane (DVCB). For example, isoprene [34], 1,3-pentadiene [35], 2,3-dimethylbutadiene [36], 1,3-hexadiene [37], and even 1-vinyl-1-cyclopentene [38] do react (eqs. (2)-(6)). 2,4-Hexadiene is inert. 

Another important class of reactions is the cyclodimerization of dienes. Thus, cycloocta- 1,5-diene is accessible from buta-1,3-diene... 

The new chiral a A, -phosphenium cations (190) undergo chelotropic cycloaddition with buta-1,3-diene to produce a cr-cycloadduct (191) (Scheme 74). The 4-1-4-cyclodimerization of 2,3-dihydroisoquinolines yields 3,7-diazatricyclo[4.2.2.2 ] dodeca-9,ll-dienes. ° Inter- and intra-molecular 4 - - 4-cycloadditions of 2-pyridones have been used in synthetic approaches to natural products such as fiisicoccin A and taxol (paclitaxel). The dimerization of pleiadene is not anh-speciflc as previously thought but yields a mixture of syn- and anft-dimers. ... 

With similar chiral sensitizers enantiomeric excesses of up to 8.2% ee were observed in the photosensitized cyclodimerization of cyclohexa-1,3-diene 34 to the exo-[4-E2]-cyclodimer 44 and the a tx-[2-l-2]-cyclodimer 45. The e do-[4-1-2]-adduct and syn-[2-l-2]-adduct were obtained as minor components. Polymenthyl benzenepolycarboxylates similar to 40 yielded dimers 44 and 45 in low yield and with enantioselectivities of up to 2.5% ee at room temperature and 4.0% ee at -41°C. Protected saccharides as chiral substituents of the photosensitizer 46 enhanced the asymmetric induction in dimethyl ether up to 8.2% ee, but only in the case of the [4-E2]-dimer 44 (Scheme 15). 

Earlier examples of copper(I)-photocatalyzed cycloalkene cyclodimerizations have been summarized in Houben-Weyl, Vol. 4/5a, pp 280-292 as was the copper(I) chloride photocata-lyzed isomerization of cycloocta-1,5-diene to tricyclo[3.3.0.02 6]octane (see Houben-Weyl, Vol. 4/5 a, p 231). This same reaction has recently been used for the preparation of 4-oxatctra-cyclo[6.3.0.02,(,.07,1 L]undecanes.10... 

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