1,5-cyclooctadiene isomers

Cyclooctadiene isomers (i.e., 1,5-cod or 1,3-cod) are selectively hydrogenated by [Ru(/74-cod)(/76-C8H1o)] (51) to produce exclusively cyclooctene in THF, under ambient temperature (20 °C) and 1 bar H2 pressure [64]. Again, cyclooctane is only detected when the diene substrate is completely transformed to the monoene. The rate of hydrogenation is higher in case of the conjugated 1,3-cycloocta-diene substrate, whereas isomerization of the non-conjugated 1,5-cyclooctadiene... 

A derivative of cyclopentyne has been trapped in a matrix. Although cycloheptyne and cyclohexyne have not been isolated at room temperatures, Pt(0) complexes of these compounds have been prepared and are stable." The smallest cyclic allene" so far isolated is l-/err-butyl-l,2-cyclooctadiene 107." The parent 1,2-cyclooctadiene has not been isolated. It has been shown to exist transiently, but rapidly dimerizes." " The presence of the rert-butyl group apparently prevents this. The transient existence of 1,2-cycloheptadiene has also been shown," and both 1,2-cyclooctadiene and 1,2-cycloheptadiene have been isolated in platinum complexes." 1,2-Cyclohexadiene has been trapped at low temperatures, and its structure has been proved by spectral smdies." Cyclic allenes in general are less strained than their acetylenic isomers." The cyclic cumulene 1,2,3-cyclononatriene has also been synthesized and is reasonably stable in solution at room temperature in the absence of air." ... 

If the insertion step following oxidative addition occurs on one of the two fragments resulting from oxidative addition, an intramolecular catalytic reaction (C—O — C—C rearrangement) takes place (example 40, Table III). It is interesting to note that two different products—2,6- and 3,6-heptadienoic acids—can be obtained from allyl 3-butenoate. Their ratio can be controlled by adding 1 mole of the appropriate phosphine or phosphite to bis(cyclooctadiene)nickel or similar complex. Bulky ligands favor the 2,6 isomer. It is thus possible to drive the reaction toward two different types of H elimination, namely, from the a or y carbon atoms. 

The strained c ,traws-l,3-cyclooctadiene 1 cyclizes quantitatively at 80 °C to the bicy-clo[4.2.0]octene 2 (equation 3). The higher homologue 3 exists in equilibrium with the bicyclic isomer 4 above 175 °C (equation 4)4. 

The ( ),( )-isomer 35 331 of 1,5-cyclooctadiene was reported to be formed (1.5% yield) when a solid residue, obtained from an UV irradiation product of bis[chloro-((Z),(Z)-l,5-cyclooctadiene)Copper(I)], was decomposed with NaCN solution. It has been claimed that the same compound 35 was also formed (2.4% yield) by the double Hofmann elimination of (Z)- or ( )-l,5-bis-(dimethylamino)cyclooctane dimetho-... 

Not all Cope rearrangements proceed by the cyclic six-centered mechanism. Thus cis-1,2-divinylcyclobutane (p. 1131) rearranges smoothly to 1,5-cyclooctadiene, since the geometry is favorable. The trans isomer also gives this product, but the main product is 4-vinylcyclohexene (resulting from 8-33). This reaction can be rationalized as proceeding by... 

Rearrangement of the stereoisomers in the cyclobutane series leads to different products, cis-1,2-Diviny IcycIobutane rearranges through a transition state similar to 30 to give ds,ds-l,5-cyclooctadiene [Eq. (4.41)]. The radical transformation of the trans isomer, in contrast, leads to 4-vinylcyclohexene242 [Eq. (4.42)] ... 

The nonconjugated 1,4-cyclohexadiene gave the same intermediate as the 1,3- isomer however 1,5-cyclooctadiene, unlike 1,3-cyclooctadiene, gave a rather stable intermediate with a band at 2145 cm-1, assigned to the 1,4,5-trihapto structure 14. A 1,3,4-trihapto structure 15 probably formed in... 

Transfer hydrogenation of dienes to monoenes 1,5-Cyclooctadiene is selectively reduced to cyclooctene by transfer hydrogenation with isopropanol catalyzed by this metal carbonyl cluster. The first step is isomerization to conjugated diene isomers. 1,5-Hexadiene is reduced under these conditions to frms-3-hexene (19%), os-2-hexene (21%), trans-2-, and cw-3-hexene (56%). Ru3(CO)i2, Os3(CO)12, and Ir4(CO)i2 catalyze isomerization of 1,5-cyclooctadiene, but are less active than Rh6(CO)i6 for transfer hydrogenation. 

The photodimerization of 2-pyridones is an efficient, regiospecific, and stereoselective [4+ 4]-cycloaddition [56] that converts two achiral aromatics into a highly functionalized tricyclic cyclooctadiene with four stereogenic centers (Scheme 9.34). For tethered pyridones, the trans isomer is usually the major product when one or both pyridine nitrogens are methylated. By contrast, in the unsubstituted systems,... 

For example, the tail-to-tail dimerization of methyl acrylate was catalyzed by ruthenium complexes such as RuHCl(C0)(Pz-Pr3)2/CF3S03Ag or even RuC13 and gave dimethyl hexenedioate isomers. Efficient catalytic systems such as Ru(rf-naphthalene)(COD)/CH3CN, where COD is cyclooctadiene, selectively led to the diester 2 in 75% yield [1] (Eq. 1). 

Scheme 7.3 Preparation of (fl//-franj-l,5,9-cyclododecatriene)nickel(0) (12) and its reactions with all-cis-C12H18 to the isomer 13 and with 1,5-cyclooctadiene to the bis(diolefin) nickel(0) complex 14...

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