Cyclooctatetraene cycloaddition reactions

As is the case for [2 + 2] cycloaddition reactions (15-61), certain forbidden electrocyclic reactions can be made to take place by the use of metallic catalysts." An example is the silver ion-catalyzed conversion of tricyclo[4.2.0.0. ]octa-3,7-diene to cyclooctatetraene " ... 

Formally, although these cyclooligomerizations can be considered as cycloaddition reactions, they are known not to occur through a direct cycloaddition process. In the best understood nickel-catalyzed reaction the dimer 12 was shown to be the key intermediate in cyclization.46,59 60 Acetylene readily undergoes cyclooligomerization in the presence of metal catalysts to form benzene and cyclooctatetraene [Eq. (13. 15)] as well as higher homologs ... 

The cobalt(I)-catalysed 6 + 2-cycloadditions of cyclooctatetraene with monosubsti-tuted alkynes produced monosubstituted bicyclo[4.2.2]deca-2,4,7,8-tetraenes in good yields.185 The 6 + 3-cycloaddition of fulvenes (145) with 3-oxidopyrylium betaines (144) formed 5-8 fused oxa-bridged cyclooctanoids (146,147), which can be manipulated by cycloaddition reactions to produce key intermediates (148,149) for the synthesis of fused cyclooctanoid natural products e.g. lancifodilactones (Scheme 38).186,187... 

The final series of five procedures presents optimized preparations of a variety of useful organic compounds. The first procedure in this group describes the preparation of 3-BROMO-2(H)-PYRAN-2-ONE, a heterodiene useful for (4+2] cycloaddition reactions. An optimized large scale preparation of 1,3,5-CYCLOOCTATRIENE, another diene useful for [4+2] cycloaddition, is detailed from the readily available 1,5-cyclooctadiene. Previously, the availability of this material has depended on the commercial availability of cyclooctatetraene at reasonable cost. A simple large scale procedure for the preparation of 3-PYRROLINE is then presented via initial alkylation of hexamethylenetetramine with (Z)-1,4-dichloro-2-butene. This material serves as an intermediate for the preparation of 2,5-disubstituted pyrroles and pyrrolidines via heteroatom-directed metalation and alkylation of suitable derivatives. The preparation of extremely acid- and base-sensitive materials by use of the retro Diels-Alder reaction is illustrated in the preparation of 2-CYCLOHEXENE-1.4-DIONE, a useful reactive dienophile and substrate for photochemical [2+2] cycloadditions. Functionalized ferrocene derivatives... 

Two Fe(CO)3 complexes of dimeric cyclooctatetraenes (29 and 30) are formed by irradiation of cyclooctatetraene iron tricarbonyl in the presence of free cyclooctatetraene, posing a formidable problem with respect to the mechanism of this cycloaddition reaction 244,403,407,4io). 

Direct irradiation of dibenzobarrelene (106a) in solution yields the di-T-methane product (107) and the cyclooctatetraene (108). Acetone-sensitized irradiation affords compound (107) only. In the crystalline phase, however, a new product (109) is obtained as well as (107) and (108). A reinvestigation of this has suggested that the biradical (110) is involved in the formation of both the ester (109) and the cyclooctatetraene (108). The formation of the biradical could involve a tri-m-methane intermediate such as (111). Other examples (106b, c) have been studied and while the solid state irradiation does not yield the appropriate diester corresponding to (109) the cyclooctatetraene obtained does have the correct substitution pattern in confirmation of the involvement of a biradical analogous to (110) rather than the (2+2)-cycloaddition reaction path which has been favoured in the past. A further study of the asymmetric induction in the di-n-methane rearrangement has examined the... 

Cycloaddition reactions of sulfur dioxide. Addition of cyclooctatetraene to SbFs (1 eq.) in liquid SO2 at -70° leads to formation of (1) and (2) the former sulfone is rapidly isomerized to (2), which has been isolated. Formation of (1) represents an unusual 1,5-cycloaddition. The trivial name for (1) is... 

Different processes must be treated separately even if they occur within the same molecule because simultaneous consideration may lead to erroneous outcome. For example, hypothetical two [2 + 2] cycloaddition reactions in cyclooctatetraene have to be considered separately. Similarly, in hexa-2,4-diene, conrotatory and disrotatory electrocyclization processes have to be treated separately while making the orbital diagram (Scheme 1.5). 

A metal atom can lead to significant changes in the reaction pattern toward electrophilic reagents. For example, tricarbonyliron derivatives of cyclo-heptatriene and cyclooctatetraene undergo facile, unprecedented, 1,3-cycloaddition reactions with electrophiles such as hexafluoroacetone and tetra-cyanoethylene. Removal of the tricarbonyliron group can lead to useful products [Eq. (58) (Green et al., 1973)]. 

Synthesis of polyacetylene is not a trivial process and this is due to the reactions of acetylene. Polymerization of acetylene can be accompanied by a variety of side reactions, thus dimerization and formation of benzene and cyclooctatetraene, cycloadditions and isomeriza-tions, as well as further reactions of the initial products are anticipated. In attempts to remove catalyst residues and impurities produced by such side reactions different methods have been adopted using a variety of purification procedures. Furthermore, polyacetylene is insoluble, infusible and susceptible to fairly rapid atmospheric degradation. Its insolubility and infusibility not only make purification difficult, but also precludes most conventional fabrication methods and procedures for modifying the polymer s bulk morphology. Hence it is important to produce high-purity material by methods which will allow convenient fabrication and control of the bulk morphology. In... 

In the reaction of l,3-diaza-2-azoniaallene salts, R N=N+=NR, with dienes, such as butadiene and 2,3-dimethylbutadiene, mono [3+2] cycloadducts are obtained. From cyclooctatetraene a bis-cycloadduct was isolated. Also, allenes and higher cumulenes undergo [3+2] cycloaddition reactions with the same salts. With butatrienes, reaction proceeds across the terminal double bonds, while pentatetraenes react across the center double bonds. 

Let us now examine tlie properties of the next higher cyclic polyene analog of benzene, 1,3,5,7-cyclooctatetraene, another 4n tt cycle (n = 2). Is it antiaromatic, like 1,3-cyclobutadiene First prepared in 1911 by Willstatter, this substance is now readily available from a special reaction, the nickel-catalyzed cyclotetramerization of ethyne. It is a yellow liquid (b.p. 152 °C) that is stable if kept cold but that polymerizes when heated. It is oxidized by air, eatalytically hydrogenated to cyclooctane, and snbject to electrophilic additions and to cycloaddition reactions. This chemical reactivity is diagnostic of a normal polyene (Section 14-7). 

Cyclooctatetraene itself does not undergo 4 + 2 cycloadditions it is its valence isomer bicyclo[4.2.0]octatriene which reacts with dienophiles.36 Use Dewar s PMO method to explain why the direct reaction with cyclooctatetraene is disfavored. 

Heating TV-ethoxycarbonylazepine with the electron-deficient diene (96) provided [2 + 4] adduct (97) and [6 -i- 4] adduct (90) in nearly equal quantities. Other examples of relatively low conversion [6 + 4] cycloadditions of substituted azepines and various dienes have been reported but are of little synthetic consequence due to low periselectivity and modest chemical yields. - Oxepin heterocycles display a range of reactions with dienes which are similar in scope to the azepine series and, as such, will not be dealt with specifically in this review. Other cyclic polyenes such as cyclooctatetraene are known to yield some [6 + 4] adducts when exposed to highly reactive diene species. For example, the potent electron-deficient diene 2,S-dimethoxycarbonyl-3,4-diphenylcyclopent ienone gives a modest amount of the corresponding [6 -I- 4] cycloadduct when reacted with cyclooctatetraene. ... 

Dewar tetrakis(trifluoromethyl)thiophene, (59), has served as a dieneophile (dipolarophile) in several cycloadditions. Diels-Alder reaction of (59) with butadiene <8icci289> and pyrrole (82JA847) has served as the starting point for the synthesis of 1,2,3,8-tetrakis(trifluoromethyl)cyclooctatetraene (60) and tetrakis(trifluoromethyl)Dewar furan (61), respectively, as illustrated in Scheme 20. It is noteworthy that (61) was unattainable by direct photolysis of the substituted furan. Moreover, (59) served as a common precursor for the preparation of tetrakis- (80JA6633) and penta-<83JA3563> (trifluoromethyl)cyclopentadienides (64) and (65), respectively (Scheme 21). Accordingly, photolysis... 

---