Bicyclic dienes structure

In an extension of this work, the Shibasaki group developed the novel transformation 48—>51 shown in Scheme 10.25c To rationalize this interesting structural change, it was proposed that oxidative addition of the vinyl triflate moiety in 48 to an asymmetric palladium ) catalyst generated under the indicated conditions affords the 16-electron Pd+ complex 49. Since the weakly bound triflate ligand can easily dissociate from the metal center, a silver salt is not needed. Insertion of the coordinated alkene into the vinyl C-Pd bond then affords a transitory 7t-allylpalladium complex 50 which is captured in a regio- and stereocontrolled fashion by acetate ion to give the optically active bicyclic diene 51 in 80% ee (89% yield). This catalytic asymmetric synthesis by a Heck cyclization/ anion capture process is the first of its kind. 

Ionic hydrogenation of the same bicyclic diene 382 by Et3SiH in the presence of CF3COOH at room temperature or at 80 °C via ions 387 and 388 is accompanied by transannular cyclizations (equation 139)192. The behavior of diene 382 under Ritter reaction conditions (MeCN, H2SO4) reveals new possibilities to control the transannular cyclizations (equation 140)193. Depending on the sulfuric acid concentration, the reaction temperature and the presence of a nucleophilic solvent, these transformations can be directed to the formation of either the bicyclic amides 389 and 390 having the precursor structure or the tricyclic products 391193. 

Bryce-Smith [2] in 1959. They found that benzene and maleic anhydride react to form a stable 1 2 adduct under the influence of ultraviolet radiation. The authors proposed that initially an ortho adduct is formed which could normally be expected to revert rapidly to the starting materials, but which would be stabilized by rapid addition of a further molecule of maleic anhydride to the bicyclic diene system. The stereochemistry of the 1 2 adduct was established by Grovenstein et al. [23] (who reported that they had independently discovered the same reaction) and, more firmly, by Bryce-Smith et al. [24] and Pettit et al. [25], The structure is depicted in Scheme 4. 

In the synthesis of occidentalol (ref. 13), a eudesmane-type compound consisting of a cis-fused decalin containing a homoannular 1,3-diene system, dihydrocarvone was converted by a typical Robinson annellation reaction to the basic reguired bicyclic structural unit. (It is of interest that a related bicyclic methyldecalenone structure, the Wieland-Miescher ketone, has been employed for the synthesis of longifolene (ref.14), copaene (ref.15) and sativene (ref.16) by three totally different strategies outside the present concept of the semi-synthetic approach). 

Bicyclic dienes of general structure 22, usually undergo addition of dichlorocarbene to the tetrasubstituted double bond to give the product 23. 

Favorable pre-orientation of the 1,5-diene system by bicyclic ring structures also enhances reactivity. For example, isomerization of trans4rans-2,S /rfl/75-bicyclo[8.4.0]tetradodecadiene is about half a million times faster than isomerization of 1,5-hexadiene. 

The authors found that by varying the level of steric hindrance associated with the dienophiles, they were able to modify the outcome of the potential double Diels-Alder reaction. When disubstituted dienophiles such as maleimides were used, the double Diels-Alder reaction occurred smoothly to yield a tetracyclic skeleton (4). If tri- or tetrasubstimted dienophiles were used, only one Diels-Alder reaction occurred to give a bicyclic diene-containing skeleton (5) that could either be treated as a discrete product or reacted further with a more reactive dienophile to again give a tetracyclic structure (6). 

Polymer-bound diene 25 was subjected to a Diels-Alder reaction with tiglic aldehyde 26 in the presence of tetrame-thylsilane (TMS)-triflate for the construction of the bicyclic core structure (Scheme 16.4). Cycloadduct 27 was obtained as a mixture of four isomers that were formed in a ratio of 67 16 16 1 endolendo lexolexo ) with the desired endo isomer predominating. To improve the stereoselectivity, tiglic aldehyde was converted into the quasi-Ca-symmetric chiral acetal 28 derived with (R,R)-2,4-pentanediol. This chiral dienophile underwent an asymmetric Diels-Alder reaction at -78°C. Removal of the chiral auxiliary from the acetal 29 resulted in the cycloadduct 27 as a mixmre of the four isomers in a ratio of 87 4 9 0.1 endolendo lexolexo ), demonstrating that the stereoselectivity of the main isomer increased from 67% to 87%. ... 

Another stereochemical feature of the Diels-Alder reaction is that the diene and dienophile partners orient so that the endo product, rather than the alternative exo product, is formed. The words endo and exo are used to indicate relative stereochemistry when referring to bicyclic structures like substituted norbornanes (Section 4.9). A substituent on one bridge is said to be exo if it is anti (trans) to the larger of the other two bridges and is said to be endo if it is syn (cis) to the larger of the other two bridges. 

Occasionally, addition products of 4//-l,2,4-triazole-3,5-diones or diazenedicarboxylic esters and oxepins have been obtained whose formation can be rationalized by an addition to the 2,4-diene system in the oxepin, e.g. formation of 10.190191 In these cases, the primary adduct usually cannot be isolated, because it undergoes a hetero-Cope rearrangement to a tricyclic or bicyclic structure in which the oxepin oxygen has become part of a carbonyl function.190 191,227... 

Geometric considerations in cyclopolymerization are optimal for 1,6-dienes (see 4.4.1.1). Instances of cyclopolymerization involving formation of larger rings have also been reported (see 4.4.1.4), as have examples where sequential intramolecular additions lead to bicyclic structures within the chain (see 4.4.1.2). Various 1,4- and 1,5-dienes are proposed to undergo cyclopolymerization by a mechanism involving two sequential intramolecular additions (see 4.4.1.3). 

Geometric considerations would seem to dictate that 1,4- and 1,5-dicncs should not undergo cyclopolymerization readily. However, in the case of 1,4-dienes, a 5-hexenyl system is formed after one propagation step. Cyclization via 1,5-backbiling generates a second 5-hexenyl system. Homopolymerization of divinyl ether (22) is thought to involve such a bicyclization. The polymer contains a mixture of structures including that formed by the pathway shown in Scheme 4.18. 

Scheme 17 Proposed transition structures for the diastereoselective bicyclization of dienes...

Mason and coworkers10 studied the chiral bicyclic derivatives 2, 3, 33 and 34, having known absolute configuration. These molecules possess a planar s-cis diene chromophore and formally their chirality is due to the presence of the D or CH3 substituents, which rule out all the symmetry planes. However, it is interesting to point out a peculiar structural... 

Regiospecilic intramolecular cycloadditions of nitrones to sulfur-substituted dienes, with 3-sulfolene precursors, has been realized (Scheme 2.217). The stereochemical outcome of these reactions is affected by the structure of the substituent (sulfide or sulfone) in the diene and by the chain length connecting the diene and nitrone (a) and (b) (see Scheme 2.211). The bicyclic products obtained from these reactions have been converted to interesting heterocyclic compounds (709). 

Bicyclic derivatives. Polyhydroxylated carbo-bicyclic derivatives may be regarded as carbasugars with the rigid structure resulting from the presence of the additional carbocyclic ring. The most convenient way for construction of the bicyclic skeleton consists of the Diels-Alder reaction of properly functionalized trienes (intramolecular version) or dienes and olefins (intermolecular). 

Recently, molecular orbital calculations (MP2/6-31G //RHF/6-31G level) which cover a series of bicyclic systems from the stable bicyclic compound 109 to the unknown 6,8-dioxabicyclo[5.1.0]octa-2,4-diene (2,3-epoxyoxepin, 120), as well as the two intermediate 8-oxa- (121) and 6-oxa- derivatives (122), were carried out58. These structures are interesting because the bicycle 120 is suggested as a transient intermediate in the metabolic oxidation of benzene leading to the muconaldehyde, which is responsible for the hema-totoxicity of benzene. 

CHR—CO—), polyoxy acids (—O—CHR—CO—), poly-l-alkylbuta-dienes (—CH=CH—CHR—CH2—). To the same class iKlong the polymers with two asymmetric atoms for every monomer unit, such as polysoibates (—CH=CH—CHA—CHB—, 32 and 33) where both eiythio- and thieo-diisotactic forms are chiral, or polyhexadiene (—CH=CH—CHA—CHA—) and poly-2,3-epoxybutane (—O— CHA-CHA-), 39, where only the thieo-diisotactic structures are chiral, and the polymers of some bicyclic monomers such as those shown in 41 and 42. Other examples are the polymers obtained by hydrogen transfer fk m substituted benzalacetone (79, Scheme 17) (266, 267). 

Cyclopolymerizations yielding more complex ring structures have also been reported [Butler, 19896, 1989]. For example, 1,4-dienes such as divinyl ether yield uncrosslinked products with little or no unsaturation and possessing different bicylic structures. The formation of one of the bicyclic structures is shown in Eq. 6-107 [Tsukino and Kunitake, 1979]. 

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