Dienes 1,5-cycloocta

Triazines are generally more reactive in [2 + 4] cycloaddition in comparison with 1,2,3-tria-zines. The wide variety of dienophiles can be employed enamines, enaminones, vinyl silyl ethers, vinyl thioethers, cyclic ketene jV,O-acetals, /V-phenylmaleimide, 6-dimethylaminopentafulvene, 2-alkylidene-imidazolidines (cychc ketene aminals), cyclic vinyl ethers, arynes, benzocyclopropene, acetylenes, and alkenes like ethylene, (Z)-but-2-ene, cyclopentene, cyclooctene and bicyclo[2.2.1]hept-2-ene, hexa-1,5-diene, cycloocta-1,5-diene, diallyl ether, cyclododeca-l,5,9-triene,... 

Reaction of borane with the cyclic diene, cycloocta-1,5-diene, is used to prepare the synthetically useful borane 9-borabicylo[3.3.1]nonane (9-BBN)... 

Cycloocta-1,5-diene Cycloocta-1,3-diene (24), cycloocta-1,4-diene (7), cyclooctene (41), cyclooctane (17) cP2Pt2w2(co)4- (PPbj)2... 

A detailed kinetic investigation of the reaction of [Ru(Cl)(H)(PPh3)3] with cycloheptatriene, cyclohepta-1,3-diene, cyclooctatetraene, penta-1,4-diene, cycloocta-1,5-diene and dimethyl maleate has been carried out spectroscopically. The major mechanism was found to involve dissociation of triphenylphosphine, followed by reaction with the organic ligand, although a second mechanism involving direct combination of the two reactants was also observed. 

The photolyses of cyclohexa-1,3-diene, cycloocta-l,3,5-triene, and bicyclo[4.2.0]octa-2,4-diene were investigated by matrix-isolation techniques at a relatively early date and certainly before reliable computational methods for IR transitions were available. As an example, both IR and UV-visible spectroscopy were employed to monitor the photoreaction of cyclohexa-l,3-diene at 240-270 nm in Ar matrices at 20 K. It was discovered that the diene photolyzed irreversibly to Z-hexa-l,3,5-triene, which photolyzed more slowly but still irreversibly to -hexa-l,3,5-triene and several other thermally unstable products. The latter could not be identified with certainty, but hexa-l,2,4-triene and exo-2-vinylbicy-clo[1.1.0]butane were proposed as possibilities. 

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 ... 

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). 

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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