Cycloocta-1,3,5-triene

For example, the electrocyclic ring closure of cycloocta-1,3,5-trienes 1 to bicyclo[4.2.0]octa-2,4-dienes 2 has been widely used for the preparation of cyclobutanes (see Houbcn-Weyl, Vol. 4/4,... 

A clean eiectrocyclic ring opening occurred at mild temperatures with the strained tricy-clo[4.3.0.07-9]nona-2,4-diene (3a) and tricyclo[4.4.0.02 5]deca-7,9-diene (3b) to give cycloocta-1,3,5-triene derivatives 4.182... 

Figure 13.23 Ring current in the Mobius transition state of the electrocyclic reaction of octa-l,3,5,7-tetraene to cycloocta-1,3,5-triene. For details see Figure 13.21. Note that the basis orbitals (atomic orbitals that are involved in the reaction) can be written with arbitrary phase. The number of antibonding overlaps (sign inversion) will...

Calculated transition structure for the electrocyclic closure of (3Z,5Z)-octa-1,3,5,7-tetraene to cycloocta-1,3,5-triene. (Adapted from reference 174.)... 

The diastereoselectivity in the reaction of 42 was proven to be independent of the polarity of the solvent used and is therefore considered a consequence of steric factors [34a], Photo-oxygenation of 1,3,5-cycloocta-triene [35] affords both the bicyclic and tricyclic endoperoxides (isolated yield 20 and 5%, respectively) as found for the heptatriene 39a, while for cyclooctatetraene [36] only the bicyclic peroxide is obtained in 26% yield. 

The results for the conrotatory ring closure of octatetraene to cycloocta-triene (Fig. 4) are shown in Table 3. For this system, the results from the RHF and DFT calculations differ significantly. Using the BLYP/6-31G method, a bond length of 2.42 A is computed for the forming bond, which is 0.22 A longer than the value obtained at the RHF/6-31G level of theory. This earlier transition state obtained by the DFT method is also indicated by the smaller... 

It is worth mentioning the synthesis of cyclic a-methylene carbamates, which were also produced via Markovnikov intramolecular nucleophilic addition of O-car-bamates, generated in situ from a propargylic amine and CO2, in the presence of Ru(cod) (cot)/phosphine as catalyst precursor (cod cyclooctadiene cot cycloocta-triene) (Scheme 8.23) [75]. 

Z,6Z,8 )-Decatetraene has been cyclizcd to give 7,8-dimethyl-1,3,5-cycloocta-triene. Predict the manner of ring closure—conrotatory or disrotatory--for both thermal and photochemical reactions, and predict the stereochemistry of the product in each case. 

Selective trapping of unstable dienes. This complex has the useful property of trapping the unstable diene tautomers of cycloocta,triene (2) and derivatives such as 5. The kinetics of complex formation with unstable dienes has been studied and arguments have been advanced to account for the selectivity observed. 

Dehydrogenation cf. 4, 485). Causing and Wilke have reported two high-yield preparations of cyclooctatetraene. Reaction of 1,5-cyclooctadiene (1) and -butyllithium-TMEDA in a ratio of 1 3 gives the crystalline compound 2 in practically quantitative yield. Cyclooctatetraene (3) is obtained from 2 by oxidation with CdCl2. The intermediate 2 can also be obtained from 1,3,6-cycloocta-triene, but not from 1,3-cyclooctadiene or 1,3,5-cyclooctatriene. 

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

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... 

It is possible in principle to deduce from the position of the first absorption band the twisting angle between the double bonds in cyclic conjugated polyenes, e.g. on the basis of a simple LCBO model50. This has been attempted for cycloocta-l,3,5-triene 184257 and cyclooctatetraene 239260. For the former it was deduced that the --system becomes... 

Ring closure to cyclobutanes via valence isomerization of cycloocta-l,3,5-trienes is also possible when carbonyl functions are present in the ethane fragment. Thus, reaction of cyclohepta-2,4,6-trienone (tropone) with diazopropane gives 8,8-dimethylcycloocta-2,4,6-trienone (16, R = H), which rearranges quantitatively to 8,8-dimethylbicyclo[4.2.0]octa-2,4-dien-7-one (17, R = H).67... 

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,... 

Keywords cycloocta-2,4,6-trien-l-one, cycloocta-2,4-dien-l-one, inclusion complex, [2+2] photocycloaddition, cyclobutane... 

The formation of the cyclooctatrienes was quenched in the presence of low concentrations of 2,5-dimethylhexa-2,4-diene or 2,3-dimethylbuta-l,3-diene. The photocyclization of the trienes was, however, unaffected by the presence of the dienes. The authors conclude that the primary photoreaction of intramolecular ortho cycloaddition involves the 3 tt, tt state of the arene and the subsequent cyclization of the cycloocta-l,3,5-triene arises from the singlet state. 

NCD = A derivative of bicyclo[4.2.0]octa-2,7-diene, a non-conjugated diene. COT = A derivative of cycloocta-l,3,5-triene. 

Scheme 33 Thermal ring opening of an ortho adduct to cycloocta-l,3,5-triene and photochemical ring closure of this triene.

A cyclooctatriene was formed upon pyrolysis at high temperature (up to 350°C) of the exo-ortho adduct from benzene and 1,4-dioxene [12] the position of the double bonds, however, was not as expected for a ring-opened ortho adduct. The ortho adduct from benzene and 1,1-dimethoxyethene [12] is an acetal and with a trace amount of acid in methanol solution it is converted into cycloocta-2,4,6-trien-l-one (Scheme 50). 

Direkte UV-Bestrahlung wandelt Cycloocta-l,3,5-trien (Formel 121) hauptsachlich in Bicyclo[4,2,0]octa-2,7-dien (Formel 122) und Tricyclo-[3,2,l,0a-8]oct-3-en (Formel 123) (58,222,340) um. Daneben werden noch all-trans-Octatetra-l,3,5,7-en (222) und Cyclo-octa-l,5-dien (58) nach-gewiesen. 

Among cyclic polyenes, cyclic dienes, trienes and tetraenes have been ring-open polymerised via the metathesis reaction. Representative of the cyclodienes most commonly used for polymerisation are 1,5-cyclooctadiene, norbornadiene (bicyclo[2.2.1]hept-2,5-diene) and dicyclopentadiene as mono-, bi- and tricyclic diolefins respectively. Cycloocta-1,5-diene metathesis polymerisation is another approach to the preparation of 1,4-polybutadiene ... 

The products are normally the cyclodimers, 4-vinylcyclohexene and cycloocta-1,5-diene, together with some trimer, cyclododeca-l,5,9-triene and possibly a small amount of divinylcyclobutane depending on the conditions and the particular catalyst, i.e.,... 

The conrotatory cyclization of fl//-cw-deca-2,4,6,8-tetraene to traw-7,8-dimethyl-cycloocta-l,3,5-triene has been studied in solvents of different polarity [157]. In agreement with a synchronous eonrotatory ring closure via an isopolar activated complex, the solvent effect is negligible as shown by the relative first-order rate constants in Eq. (5-52). 

---