1,5-Cyclooctadiene, from 1,3-butadiene

Several cyclic oligomers 1-5 are prepared from butadiene using transition metal catalysts. The preparation of 1,5-cyclooctadiene (3 1,5-COD) by a catalyst prepared from Ni(CO)4 and phosphine is the first report on cyclooligomerzation of butadiene [1], However, the activity of this catalyst is low due to strong coordination of CO. Catalyst prepared from TiCU and EtjAl has higher catalytic activity for the formation of 1,5-COD and 1,5,9-cyclododecatriene (1,5,9-CDT 4). Also Ni(0) catalysts are active for the preparation of COD and CDT. In addition to COD and CDT, the cyclic... 

Cyclooctadiene (COD) is an intermediate for the manufacture of poly-octenamers, while 1,5,9-cyclododecatriene (CDT) is the starting material for the manufacture of dodecanoic acid and lauryl lactam. The latter is converted to the polyamide fiber Vestamide (DuPont). Both COD and CDT are made from butadiene (Equations 21 and 22). 

Diradical intermediates may occur in other types of cycloadditions and cycloreversions. Kinetic data for the thermal transformation of ci5,ci5-l,5-cyclooctadiene to butadiene and 4-vinylcyclohexene are consistent with a diradical intermediate the same intermediate may be involved in the reaction of butadiene leading to [2 + 2] adducts and to the Diels-Alder product 4-vinylcyclohexene. - That a Diels-Alder product may arise from a stepwise path is not as unimaginable today as may have been the case just a few years ago. In more elaborate contexts as well, regiochemistry may be successfully rationalized through estimations of the relative stabilities of diradical intermediates. ... 

Catalytic cyclodimerization of dienes can also be performed selectively. 1,5-Cyclooctadiene, dimethylcydooctadienes, and 6-methyl-2,4,7-nonatriene can be obtained from butadiene, isoprene, and 1,3-pentadiene, respectively, upon treatment with a catalytic amount of (C5Me5)RuCl(diene) and AgOTf... 

We had established in previous catalytic reactions involving complex 24 that this precatalyst was activated by the removal of the cod (1,5-cyclooctadiene) from the ruthenium by its reaction with the alkyne substrate via a [2 + 2 + 2] cydization as illustrated in Equation 1.64 [57]. Thus, not only does this reaction constitute an activation of the Ru complex 24 by reacting off the cod, it also serves as a novel atom economic reaction in its own right. Both internal and terminal alkynes participate. The overall atom economy of this process is outstanding since cod itself is simply available by the nickel-catalyzed dimerization of butadiene. Thus, the tricyclic product is available by the simple addition to two molecules of butadiene and an alkyne with anything else only needed catalytically. 

Cyclooctene is obtained by partial reduction of 1, 5-cyclooctadiene, which in turn is available from butadiene (p. 369). Co-metathesis between the polyoctene and cis-1,4-polybutadiene gives a rubber which is very stable to heat, oxygen and light, is easily moulded and is readily combined with other rubbers by vulcanization. 

As the outer electron configuration of cobalt is 3d 4s as described above, cobalt is liable to bond with nine electrons to satisfy the 18-electron rule. Hence, cobalt bonded with five electrons from a cyclopentadienyl ring is liable to bond with four electrons such as those from butadiene, cyclooctadiene and a variety of other diene compounds. For example, cobalt acetylactonate reacts with cyclopentadiene and... 

The cyclooctadienes, easily obtained from butadiene-1.3, illustrated the complexity of the reaction paths of such dienes [253]. 

One other reaction deserves mention. From bis(cyclooctadiene)nickel and butadiene (31), and in the presence of an isocyanide (RNC, R = cyclohexyl, phenyl, tcrt-butyl) two organic oligomeric products are obtained, 1 -acylimino-11 -vinyl-3,7-cycloundecadiene and 1 -acylimino-3,7,11 -cyclo-dodecatriene. In each, one isocyanide has been incorporated. An analogous reaction with carbon monoxide had been reported earlier. The proposed mechanism of these reactions, via a bis-7r-allyl complex of nickel, is probably related to the mechanism described for allylpalladium complexes above. 

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). 

The nickel-catalyzed [4 + 4]-cycloaddition of butadiene to form cyclooctadiene was first reported by Reed in 1954.90 Pioneering mechanistic and synthetic studies largely derived from the Wilke group advanced this process to an industrially important route to cyclodimers, trimers, and other molecules of interest.91-94,943 95,96 While successful with simple dienes, this process is not useful thus far with substitutionally complex dienes as needed in complex molecule synthesis. In 1986, Wender and Ihle reported the first intramolecular nickel-catalyzed [4 + 4]-reaction of... 

Type [55] complexes are obtained from cyclooctadienes (74), too, but also from cy-clododecatrienes (59, 117), hexadienes (765), and butadienes (755). Some of these reactions also lead to tetraruthenium olefm clusters. Of these, the complex [7 ] has been mentioned already, and is obtained from cyclooctadiene (74, 75, 283), whereas the complex [59] results from cyclododecatriene (56, 59). 

A much less strained Mobius [4 + 4] transition state can be formed from two s-cis molecules of 1,3-butadiene. When 1,3-butadiene is heated by itself, a few percent of 1,5-cyclooctadiene is formed, but it is not known for sure whether the mechanism is that shown ... 

Nickel-triarylphosphite complexes catalyze the dimerisation of butadiene to cyclooctadiene. Cyclododecatriene is an unwanted by-product, which results from trimerization catalyzed by the same catalyst. Table 3.2 shows the product yields using various ligand-metal complexes (the remainder in each case is a tarry polymeric material). 

Table X, however, shows clearly that, in contrast to the butadiene-ethylene system, triphenylphosphine is the most successful ligand. We will return to this point later. The preparation of DMCDeT on a laboratory scale can be conveniently carried out by dissolving the nickel-ligand catalyst [which may be prepared by reduction of nickel acetylacetonate or directly from bis(cyclooctadiene)nickel and triphenylphosphine] in a solution of butadiene in toluene. Butyne is then added to give a butadiene-to-butyne ratio of 5-10 1. The reaction is conducted at 20° C and the contraction in volume is observed. The reaction is terminated at the break in the contraction curve (Fig. 3).

Hegedus and Varaprath studied the reactions of various bromodienes with Ni(CO)4 and with bis(cyclooctadiene)nickel. l-Bromo-2,5-hexadiene and 2-bromomethyl-1,3-butadiene give the stable products 62 and 63, respectively, which resemble allyl nickel halides in their properties (217). Similar compounds had been prepared several years previously from geranyl halides (218). l-Bromo-2,4-pentadiene and l-bromo-2,4-hexadiene, however, formed intractable materials which could not be isolated and purified. In these cases the red color of the solution which was first produced faded and NiBr2 was deposited. The desired compounds, however, could be generated in situ at — 30° C and used in coupling reactions with aryl, alkenyl, and allyl halides (217). 

Replacement of cyclooctadiene in the zinc derivative 39 by butadiene leads to the trinuclear complex 40, which can be converted by reaction with lithium metal into 41 and metallic zinc. Under mild reaction conditions, 41 cannot be obtained directly from 34 and butadiene. 

Cyclo- and linear-dimerizations of 1,3-dienes were accomplished by means of a cationic ruthenium catalyst derived from [Cp RuCl(l,3-diene)] and AgOTf (Scheme 4.48) [96]. In THF, 1,3-butadiene was treated with the cationic ruthenium catalyst at 70 °C for 10 h to afford 1,5-cyclooctadiene in 89% yields. Similarly, isoprene underwent [4 -I- 4] cycloaddition in a head-to-tail fashion to yield quantitatively 2,6-dimeth-yl-l,3-cyclooctadiene and 3,7-dimethyl-l,5-cydooctadiene in a ratio of 21 79. On the O ther hand, a head-to-tail linear dimer was obtained in 95% yield from 1,3-pentadiene. 

Finally, the cycloisomerization of 4-vinylcyclohexene (a butadiene dimer) to bicyclo[3.3.0]-2-octene (6) was found to occur at 250° over a silicophosphoric acid catalyst (11), along with a very large amount of hydrogen transfer (ethylcyclohexenes, methylethylcyclopentenes, ethylbenzene) and polymerization, a reaction closely related to that of limonene (5). A much better yield of the same hydrocarbon (6) was obtained from 1,5-cyclooctadiene (72% at 200°) with the same catalyst (25). 

Poly(l,4-butadiene) segments prepared by the ruthenium-mediated ROMP of 1,5-cyclooctadiene can be incorporated into the ABA-type block copolymers with styrene (B-106) and MMA (B-107).397 The synthetic method is based on the copper-catalyzed radical polymerizations of styrene and MMA from the telechelic poly(butadiene) obtained by a bifunctional chain-transfer agent such as bis(allyl chloride) or bis-(2-bromopropionate) during the ROMP process. A more direct route to similar block copolymers is based on the use of a ruthenium carbene complex with a C—Br bond such as Ru-13 as described above.67 The complex induced simultaneous or tandem block copolymerizations of MMA and 1,5-cyclooctadiene to give B-108, which can be hydrogenated into B-109, in one pot, catalyzed by the ruthenium residue from Ru-13. 

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). 

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