Isomerization of 1,5-cyclooctadiene

Photolytic reactions of dienes frequently give complex mixtures of rearranged products. Described here, however, is a photolytic isomerization of 1,5-cyclooctadiene (present in solution, in part, as a complex with cuprous chloride) that affords a good yield of one product. 

In 1968, while investigating the efficacy of bis(rj-cyclopentadienyl)-diphenyltitanium as a catalyst for the isomerization of 1,5-cyclooctadiene to 1,3-cyclooctadiene, Hagihara and co-workers found that the presence of CO inhibited the isomerization. Under the reaction conditions imposed, Cp2Ti(CO)2 (1) and benzophenone were isolated. Furthermore, 1 showed poor catalytic activity for this isomerization (34). 

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. 

Statistical methods can often be used to understand what variables are important for the preparation of catalysts, for the optimization of selectivity and conversion and other phenomena. Screening and experimental design methods have been used by Ebert et al. to optimize the selectivity of isomerization of 1,5-cyclooctadiene to 1,4-cyclooctadiene.38 Silica supported Ir4(CO)i2 was used as a catalyst and experimental data from the experimental design were used to optimize the yield of 1,4-cyclooctadiene with selectivity of 50 %. 

Polymer-supported titanium catalysts can be regenerated. A series of polymer-supported CpCp TiC (Cp = polymer substituted Gp rings) has been reduced by PPMgBr in situ, and used as catalysts for the hydrogenation of styrene, the isomerization of 1,5-cyclooctadiene and 1,5-hexadiene, and the reduction of carbonyl compounds. In some cases, the introduction of a polymer ligand on the Cp ring restricts the aggregation of active sites and the formation of inactive dimeric titanium species, and results in an activity increase. 

The photochemical isomerization of 1.5-cyclooctadiene iron tricarbonyl (7) to 1.3-cyclooctadiene iron tricarbonyl (8) mentioned in section E 3 is an example of ligand isomerization by formal shift of C=C bonds 284>. No deuterium is incorporated in the complex if the isomerization is carried out in a D 2-atmosphere. It appears not impossible, that the rearrangement occurs by a skeletal reorganization involving cleavage of C—C bonds and not hydrogen shift 284>. 

The planar clusters [W2Pd2Cp2(CO)6(PR3)2] (3e, 3f) catalyze the hydrogenation and isomerization of 1,5-cyclooctadiene and the hydrogenation of phenylacetylene to a mixture of styrene (major) and ethylbenzene. These clusters also catalyze the photoinitiated hydrosilation of 1-pentene and butadiene oligomerization. ... 

Yu. G. Osokin, M. Ya. Grinberg, and V. Sh. FeTdblyum [Kinet. Catal., 17, 1047 (1976)] studied the liquid phase isomerization of 1,5-cyclooctadiene in the presence of an iron pen-tacarbonyl catalyst. These researchers attempted to model the reactions of interest in two ways ... 

Hassan A. Tayim and J. C. Bailar, Jr., Homogeneous Catalysis in the Reactions of Olefinic Substances. VIII. Isomerization of 1,5-Cyclooctadiene with Dichlorobis-(triphenyl-phosphine)platinum(II), J. Am. Chem. Soc. 89 3420 (1967). 

Under irradiation at 254 nm, the complex [RhCl(l,5-COD)]2 causes the isomerization of 1,5-cyclooctadiene to a mixture of 1,3-cyclooctadiene, 1,4-cy-clooctadiene and bicyclo [4.2.0]octene-7 (Scheme 7.2). An additional product of this photoreaction is the compound bicyclo [3.3.0]octene-2. The isomerization reactions of 1,5-cyclooctadiene likely proceed via Rh(III) alkyl hydride intermediates. The bicyclic products result from photoreactions of either... 

Borabicyclo [3.3.1] nonane [280-64-8], 9-BBN (13) is the most versatile hydroborating agent among dialkylboranes. It is commercially available or can be conveniendy prepared by the hydroboration of 1,5-cyclooctadiene with borane, followed by thermal isomerization of the mixture of isomeric bicychc boranes initially formed (57,109). 

As with Pd bonds, Pd H will add to unsaturated functional groups see Hydride Complexes of the Transition Metals). In the case of alkynes, the Pd H addition is cis, to give vinyl complexes. The addition of a Pd H bond to an alkene will normally generate a Pd alkyl with jS-hydrogens, which can undergo further jS-elimination. This process can lead to alkene isomerization. However, palladium complexes have not proved as useM as those of other transition metals for alkene isomerization. While 1,5-cyclooctadiene can be isomerized to 1,3-cyclooctadiene with PdCl2(PhCN)2, palladium on charcoal is a more convenient and active catalyst for this isomerization. 

The reaction of selenium monochloride with propylene was also shown to give the two isomeric bis(/ -chloroalkyl)selenides (86) and (87) via the episelenium intermediate (85) (Scheme 17) <69JOC4003>. As compared to the reaction of propylene with sulfur monochloride, the isomer distribution (86) and (87) remains essentially identical to that observed in the sulfur case within experimental limits. On the other hand, the reaction of 1,5-cyclooctadiene (88) with selenium monochloride was reported to result in the formation of 2,6-dichloro-9-seleno-bicyclo[3.3.1]nonane (89), which can be transformed into the starting cyclooctadiene (88) by treatment with potassium cyanide or lithium aluminum hydride via the episelenium intermediate (90) and episelenide (91) as shown in Scheme 18 <69JOC4003>. 

Isonurization of dienes. This strong base effects isomerization of 1,5- or 1,3-cyclooctadiene to cij-bicyclo[3.3.0]-A -octene (5) in 50-65% yield (stirred in an autoclave at 175° for 22 hrs.). In the case of 1,3-cyclooctadiene, isomerization to... 

Borabicyclo[3.3.1]nonane (9-BBN) has been prepared by the thermal redistribution of 9-n-propyl-9-BBN, and the hydroboration of 1,5-cyclooctadlene with borane-tetrahydrofuran complex followed by thermal isomerization of the mixture of dialkylboranes at BS C. Solutions of 9-BBN have been prepared from the hydroboration of 1,5-cyclooctad ene with borane-methyl sulfide in solvents other than THF.6 The present procedure involves the cyclic hydroboration of 1,5-cyclooctadiene with borane-methyl sulfide in 1,2-dimethoxyethane.7 Distillative removal of the dimethyl sulfide in this special solvent system provides a medium that gives high purity, large needles of crystalline 9-BBN dimer in excellent yield. The material can be handled in air for brief periods without measurable decomposition. 

Via stereoselective ethenolysis of 1,5-cyclooctadiene (COD), Bykov et al. [25] prepared l,d5-5,9-decatriene, a precursor for the synthesis of many ds-isomeric insect sex pheromone compounds. In the presence of the MoCl5/Si02/Me4Sn catalyst system, at 20 °C and an ethene pressure of 25 bar, a 80 % conversion of COD was obtained with a selectivity of 68.4% for l,ds-5,9-decatriene. From this triene, many long-chain (CiQ-Cig) unsaturated acetates, alcohols and aldehydes can be obtained with the required biologically active cis conformation. Cross-metathesis of cyclooctene with a-olefins in the presence of the same catalyst gave... 

The complex [(OC)4Fe(//-PPh2)Pd( -Cl)]2 is a selective catalyst for the isomerization of 1-octene to 2-octene and the hydrogenation of 1-hexyne in the presence of 1-hexene. At 448 K, under 100 atm H2, 93% of a sample of 1-hexyne in benzene was reduced to hexene and only 3% to hexane. This is unexpected because palladium is usually an excellent catalyst for the hydrogenation of olefins. It also catalyzes the carbonylation of 1-octene under mild conditions (348 K, 50 atm). The total yield of esters was ten times greater than with [PdCl2(PPh3)2] as a catalyst. This bimetallic complex was also an effective catalyst for the carbonylation of 1,5-cyclooctadiene. ... 

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