Cycloocta

Cyclooctatetraene is relatively stable but lacks the special stability of benzene Unlike benzene which we saw has a heat of hydrogenation that is 152 kJ/mol (36 kcal/mol) less than three times the heat of hydrogenation of cyclohexene cycloocta tetraene s heat of hydrogenation is only 26 kJ/mol (6 kJ/mol) less than four times that of CIS cyclooctene... 

The April 1993 issue of the Journal of Chemical Educa tion ipp 291-293) contained an article about cycloocta tetraene entitled Don t Stop with Benzene Keep Going with Cyclooctate traene appeared in the Jan uary 2000 issue (pp 55-57)... 

Other aromatic ions include cyclopropenyl cation (two rr electrons) and cycloocta tetraene dianion (ten tt electrons)... 

Section 11 18 Although cychc conjugation is a necessary requirement for aromaticity this alone is not sufficient If it were cyclobutadiene and cycloocta tetraene would be aromatic They are not... 

For monocyclic prefixes other than benzo-, the following names are recognized, each to represent the form with the maximum number of noncumulative double bonds cyclopenta-, cyclohepta-, cycloocta-, etc. 

Cyclohexyl[l 5]crown-5, potassium complex equilibrium constant, 7, 742 (73MI52101) Cyclohexyl[15]crown-5, sodium complex equilibrium constant, 7, 742 (73MI52101) Cycloocta[ 1,2-c 5,6-c ]difuran H NMR. 4. 564 (70JA973) Cyclopenta[h][2.2.4]cyclazine... 

Cycloocta l,5-dlona-2 -(or 3 )earboxyllc acid mattiyl aster (3) (4), A solution d eyclohe)(a-1,3-dlone 1 (1.00 g, 8.9 mmol) in methyl acrylate 2 (100 g. 1.16 mmol) was Irradiated with a X 450 W medkjm pressure lamp under Na through a pyrex (Iter (or 5 h. The semicrystalliM residue obtained after removal oi the solvent, was crystallized from MeOH, the n ther liquor, separated by preparative TLC (PhH Et20) and the main fraction oonMned vrilh the crystals to gM 1.06 g of 3 (60%), mp 104-105°C (MeOH), The second minor fraction (from TLC) gave 4, mp 91 C (MeOH). 

Arene (e.g. benzene, substituted benzenes) cycloheptatriene, cycloocta-l,3,5-triene Tropylium (cycloheptatrienyl)... 

Synthesis, stereochemistry, and transformations of cyclopenta-, cyclohexa-, cyclohepta-, and cycloocta-annelated pyrimidines 98AHC(69)349. 

Since borane BH3 reacts with only one or two equivalents of a sterically hindered alkene, it is possible to prepare less reactive and more selective borane reagents R2BH and RBH2 respectively. In addition to disiamylborane 8 and thexylbo-rane 10, the 9-borabicyclo[3.3.1]nonane (9-BBN) 14 is an important reagent for hydroboration, since it is stable to air it is prepared by addition of borane 2 to cycloocta-1,5-diene 13 ... 

The interest in azacyclooctatetraenes is mainly due to their structural similarity to cycloocta-tetraene.1 3 Most synthetic efforts have concentrated on a comparison of the unusual chemical and physical properties of cyclooctatetraene with its aza analogs. Besides studies concerning the aromaticity, the primary focus of much work has concerned the stability of the eight-membered ring and its valence isomerization. 

An example of a rhodium(I) complex with a tridentate phosphine is shown in Figure 2.16 it is formed by the usual route, reaction of the phosphine with [RhCl(cycloocta-1,5-diene)]2. 

This has a folded structure (Figure 2.27) similar to that of rhodium carbonyl chloride (Figure 2.18) with ethene acting as a two-electron donor, but ethene is more weakly held and readily displaced by CO and certain alkenes (e.g. cycloocta-1,5-diene). 

Not all Cope rearrangements proceed by the cyclic six-centered mechanism. Thus c/5-1,2-divinylcyclobutane (p. 1445) rearranges smoothly to 1,5-cycloocta-... 

The reaction of the stabilized yUde 46 (a-vinyl substituted) with the cycloocta-dienyl Pd(II) allows the synthesis of a novel complex, the (rj -allyl)palladium 47, in which the olefmic double bond participates in the coordination (Scheme 20) [83]. The coordination of the bis-yUde 48 with the same starting Cl2Pd(COD) leads to the formation of another new palladium complex 49 via COD exchange reactions. A C-coordination mode takes place between the carbanionic centers of the bis-ylide and the soft palladium and two stereogenic centers of the same configuration are thus created [83]. In contrast to the example described in Scheme 19, the Cl2M(COD) (M=Pd or Pt), in presence of a slightly different car-... 

Valence isomerism of the 7,8-bis(phosphino)cycloocta-l,3,5-trienes (73) has been studied in a range of compounds, and the... 

Two papers describe the hydrophosphonation of unsaturated cyclic hydrocarbons. With dialkyl phosphonates, cycloocta-1,5-diene affords the phosphonate esters (66) but in the presence of strong acids, or when using the moderately strong l PtOXDH itself, the monocyclic esters (67) are also formed. Cyclododeca-1,5,9-triene affords a mixture of polycyclic... 

Irradiation of cycloocta-2,4-dien-l-one (55) in pentane gives a racemic photodimer, anti-tricyclofSAO.O Jhexadeca- , 11 -diene-3,16-dione (60) in 10% yield along with polymeric materials 34). Efficient and enantioselective photodimerization of 58 was achieved by irradiation of the 2 1 inclusion complex 59 formed between 2 a and 5813). When a solution of 2a and an equimolar amount of 58 in ether-hexane (1 1) was kept at room temperature for 12 h, 59 was obtained as colorless needles of mp 105 to 108 °C. Irradiation of 59 in the solid state for 48 h gave (—)-60 of 78 % ee in 55 % yield. 

Tetranitromethane adds across various non-conjugated dienes to give cyclic products. The products with norbomadiene and cycloocta-1,5-diene are subject to spontaneous violent decomposition. 

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