14- Membered cyclic triene

Highly strained four-membered cyclic disilane adds to the central C=C bond of a cumulated triene in the presence of Pd(PPh3)4 in a regioselective manner (Equation (39)).82,83... 

The carbolithiation of six- to nine-membered 3-methylenecycloalka-l,4-dienes has been investigated and shown to be an exceptionally facile and general process.69 Primary, secondary, and tertiary organolithium reagents may be employed for carbolithiation of cyclic trienes with uniform efficiency, generating cyclic pentadienyl carbanions. The six-electron pentadienyl systems display unique reactivity as a function of ring size. 

Two isomeric 1,5,9-cyclododecatrienes, namely, trans,trans,cis-CijH 18 (XLVI) and trans,trans,trans-CuHis (XLVII), are formed in good yield by the cyclic trimerization of butadiene using certain Ziegler-type catalysts 247, 250, 251, 252). The formation of these 12-membered ring hydrocarbons probably proceeds via metal 7r-complexed intermediates. When the cyclic triene (XLVII) is treated with nickel acetylacetonate and... 

A six-membered cyclic conjugated triene system is called an aromatic ring. The individual single and double bonds are shown in individual canonical structures, while the resonance hybrid indicates the delocalisation that takes place in reality. 

A novel triolefin ligand (E,E,E)-l,6,ll-tris[(2,4,6-triisopropylphenyl)sul-fonyl]-l,6,ll-triazacyclopentadeca-3,8,13-triene was anchored to a polystyrene support [47] (Scheme 9). Thus, the 15-membered triene 24 bearing a styrene group underwent polymerization with styrene and DVB to afford the cross-linked PS-supported cyclic triene 25. The supported macrocyclic triene 25 was treated with Pd(PPh3)4 to give the palladium complex 26. The complex... 

Previous studies showed that the normal RCM reaction of simple triene (61) gave a poor regioselectivity to afford a mixture of five- and six-membered cyclic ethers. To resolve this problem, the authors tested a selective relay alkene RCM strategy, where the precursor (62) was modified to arm with an allyloxymethyl side chain. In this case, the initial ruthenium carbene species was selectively formed at the terminal alkene position of the allyloxymethyl side chain for both steric and electronic... 

Cyclononatriene, the smallest cyclic [3]cumulene isolated so far, polymerizes when its solutions are concentrated57. On the other hand, several radialenes have been isolated which represent cyclodimers of seven- and eight-membered 1,2,3-trienes (Scheme 9). 

There seems to be no great difference in the free energy between acyclic triene and the cyclic diene. This is because of smaller strain in the six-membered ring as compared with the four-membered one. On the other hand in 6n electron system in electrocyclic process there is more efficient absorption in the near regions of u.v. spectrum. This is why under both thermal and photochemical conditions, the (1, 6) electrocyclic reactions are reversible. Side reactions are more frequent in reversible. Side reactions are more frequent in reversible transformations of trienes than in dienes. The dehydrogenation of cyclic dienes to aromatic compounds may also occur in the thermal process. On heating cyclohexadiene yields benzene and hydrogen. 

Prolonged irradiation of the mixture leads to the formation of a huge variety of secondary products due to competing photoreactions of the triene members of the series P, T and D. Many of these are formed as a result of the more common triene photoprocesses which have already been discussed. Many more are formed via less generic processes which involve the cyclic moieties at the two ends of the triene or intervention of the solvent in either catalytic or direct fashion. The so-called toxisterols arise from irradiation... 

A special case of the preparation of cyclobutanes from 1,5-dienes via valence isomerization is the use of acyclic or cyclic 1,5,7-trienes which give four-membered rings via an intramolecular [7t + 7ts2] cycloaddition (Diels-Alder reaction). This variant is illustrated for monocyclic tricnes 18 and 20 where two 71-bonds are transformed into a-bonds, resulting in tricyclic compounds 1968 and 21.09... 

Conjugated linear trienes were reported to undergo cyclization to form seven-membered ring systems.112 Cyclic polyenes, in turn, isomerize to yield bicyclic compounds. In the transformation of nonatriene (10), the role of the base was demonstrated to catalyze the formation of the conjugated triene [Eq. (4.23)], which... 

Appl and Huisgen have proposed a mechanism for the formation of the cyclic amidines which involves an azacyclopropene intermediate, the 7-azabicyclo-[4 1 0]hepta-2,4,6-triene (141) which later reacts with aniline to form the 7-membered ring (see, however, refs. 18, 95). 

The majority of the known heterocyclic dienes are pentadienes, largely as a result of the discovery that alkynes react with alkali metals and form dianions via dimer addition of the acetylene anion radical. A method that has become useful for the generation of larger cyclic dienes is the addition of an organometallic dihydride to a suitable dialkyne. Synthetic approaches to six-membered dienes tend to be unique for each system, and no general method has been developed. Some of the six-membered heterocyclic dienes have been converted to trienes for the study of systems that may be aromatic. 

An early demonstration of the template effect in the synthesis of macrocyclic ligands was the metal-ion-controlled cyclic condensation of 2,6-diacetylpyridine with 3,3 -diaminodipropylamine to give complexes of the 14-membered N4 ring (118), usually abbreviated (Me2pyo[14]triene i ). Effective template ions include Ni", Co" and Cu". Well-characterized iron complexes have not been... 

Diazepines cannot have the cyclic electron delocalization found in all other heterocycles that have been discussed, although they are in the state of maximum unsaturation for a 7-membered ring (cyclohepta-triene). 

In theory, conjugated trienes can undergo [6 + 3]-cycloaddition with Pd-TMM to give nine-membered ring compounds. So far, all the known examples involve tropone derivatives as starting materials. Their cyclic structure and reduced conformational flexibility promote the [6 + 3]-cycloaddition at the expense of the competing [2 + 3] and [4 + 3]-cycloadditions. A recent example includes the addition of a methyl-substituted analog of 1 to 2-phenyltropone. ... 

The frontier molecular orbitals control the motions of the atoms in an electrocyclic reaction independent of the equilibrium constant for the reaction. The position of an equilibrium is controlled by AG°. Both a conjugated diene and a triene can undergo thermal electrocyclic reactions. In both cases, the cyclic compounds have more O bonds and fewer Jt bonds. However, AG° is favorable only for the triene. The strain of the four-membered ring of the diene effectively reverses the relative stability of the reactants and products in the cyclization of the diene. 

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