Dienyne compounds

Cyclopropanation progressed through a cyclopropyl methyl carbene complex of gold 312, which is active toward further cyclopropanation with an intramolecular alkene unit. Echavarren and coworkers reported that dienyne compounds 311 gave tricyclic cyclopropanes 313 in good yields (Scheme 1.153) [220]. 

Guanacastepene A (444) is a novel tricyclic diterpene with fused five-, seven-, and six-membered rings. The possibility of constructing polycyclic compounds via tandem RCM of dienynes was used in Hanna s synthesis of a highly functionalized tricyclic system 443 related to 444. Under the conditions outlined in Scheme 87, trienyne 440 provided the desired tricycle 442 in a single step, as a result of sequential enyne RCM followed by RCM of intermediate 441. Compound 442 was then further functionalized to 443 [182]. 

Lewis-acid catalysis is effective in intermolecular as well as intramolecular /zomo-Diels-Alder reactions. Thus, complex polycyclic compounds 93 have been obtained in good yield by the cycloaddition of norbornadiene-derived dienynes 92 by using cobalt catalyst, whereas no reaction occurred under thermal conditions [91] (Scheme 3.18). 

An example of this reaction in an acyclic case is given in equation 21. Dienyne 55 afforded compound 56 in a highly selective 1,4-addition. In this case the relative amount of the trans chloropalladation adduct was higher than in the reaction of 53 and the chlorovinyl group was 90% E54. 

Diver has recently reported new entries for the assembly of tetracyclic compounds.304 Interestingly, ruthenium catalysts for metathesis have also yielded tricyclic products by incorporating a cyclopropane from dienynes, a process reminiscent of Dixneuf s work (see above). 

Recently, four-component coupling reactions of aldehydes, alkynes, dienes, and dimethylzinc catalyzed by a nickel complex have been reported (Equation (78)).435 Similarly, l,c< -dienynes react with carbonyl compounds and dimethylzinc in the presence of an Ni catalyst to afford the corresponding cyclized products. 

In turn, the propensity of 1 to respond to steric hindrance can be used to control the site of initiation of an RCM reaction in a polyene substrate (Scheme 9) [20]. Thus, dienyne 25 reacts with the catalyst regioselectively at the least substituted site the evolving ruthenium carbene 26 undergoes a subsequent enyne metathesis leading to a new carbene 27, which is finally trapped by the disubsti-tuted olefin to afford the bicyclo[4.4.0]decadiene product 28. By simply reversing the substitution pattern of the double bonds, the complementary bicyclo [5.3.0] compound 32 is formed exclusively, because the cyclization cascade is then triggered at the other end of the substrate. Note that in both examples tri-substituted olefins are obtained by means of a ruthenium based metathesis catalyst [20] ... 

Unsymmetrical dienynes react regioselectively with organolithium compounds at the less substituted double bond (Scheme 2.37). Thus, addition of n-butyllithium to 2-methylhexa-l,5-dien-3-yne (107) led after hydrolysis to vinylallene 108, whereas the corresponding carbolithiation of the linear isomer 109 furnished product 110 with 55% yield [68]. 

We found that 43 (R1 = R2 = Me) and 44 lead to a mixture of the diallenes meso-and rac-45, which can be characterized by spectroscopy without doubt at low temperature [104], The isolation of 45 (R1 = R2 = Me) failed because this compound rearranged rapidly at room temperature most probably to the dienyne 46. Braverman et al. [105] analyzed spectroscopically the diallenes 48 resulting from diols 47 and the reagent 44. In one case, even isolation was possible. However, the cumulenes 48 cydize irreversibly to mixtures of the stereoisomers of the stable compounds 49 at room temperature, mostly at lower temperature. 

Group-selective enyne metathesis of dienyne 127f having a large substituent on the alkyne proceeds in the presence of aUcene 130 to give small ring compound 131... 

The dienyne ether is very oxygen-sensitive and polymerizes rapidly at room temperature. The compound can be stored for a few days at -80 C in an undiluted state. 

Grubbs reported an ingenious method for synthesizing bicyclic compounds from dienynes taking advantage of the... 

Dienyne metathesis has been further extended to the synthesis of polycyclic compounds 28 from poly ene-ynes 27 by one step (Scheme 9). 

Synthesis of a polyoxygenated bicyclic compound containing a medium-sized ring is achieved via tandem metathesis of the dienyne derived from D-ribose (Equation (11)). ... 

The alkyne insertion reaction is terminated by anion capture. As examples of the termination by the anion capture, the alkenylpalladium intermediate 189, formed by the intramolecular insertion of 188, is terminated by hydrogenolysis with formic acid to give the terminal alkene 192. Palladium formate 190 is formed, and decarboxylated to give the hydridopalladium 191, reductive elimination of which gives the alkene 192 [81]. Similarly the intramolecular insertion of 193 is terminated by transmetallation of 194 with the tin acetylide 195 (or alkynyl anion capture) to give the dienyne 196 [82], Various heterocyclic compounds are prepared by heteroannulation using aryl iodides 68 and 69, and internal alkynes. Although the mechanism is not clear, alkenylpalladiums, formed by insertion of alkynes, are trapped by nucleophiles... 

While the syntheses of the acyclic precursors in the examples above each require a couple of steps, symmetrical dienynes with a central triple bond and heteroatoms in the tethers are more easily accessible. They can yield heterotricyclic compounds by the same reaction mode, for example, the diaza- and dioxatricycles 121 are obtained starting from dienynes 119 (Scheme 18) [73]. Yields were best (90%) with N-tosyl linkers, with N-Boc groups the reaction was slower (41% yield), and with N-benzyl linkers only decomposition occurred. This may be due to coordination and blocking of the catalyst by the more Lewis-basic amines. The cis- and frans-diastereomers of 121 were formed in a ratio of 1.8 1, and this ratio did not change in other solvents, at different temperatures, with other catalyst precursors or under high pressure (10 kbar). In view of the apparent influence of the tether, the unsymmetrical oxazaprecursor 122 gave a 7 3 mixture of tricycles 123 and 124. Obviously, the hydridopalladation of the triple bond occurred with some regioselectivity such that intramolecular carbopalladation of the allyl-amine predominated. It is noteworthy that in these cases the intramolecular Diels-Alder reactions of the intermediate trienes 120 already occur under the employed conditions, i.e. at 80 °C. 

Our group has used a combined metathesis-PKR for the synthesis of tricyclic compounds in one step. The process starts from pure cobalt complexed dienynes 52. The cobalt cluster acts first as a protecting group to avoid undesired enyne metathesis processes. The methodology allows the formation of tricyclic [6.5.5] (53) and [7.5.5] (54) structures including, in some examples, oxygen or nitrogen. Tricycles 53 are obtained in a total stereoselective manner, while compounds 54 are formed as mixtures of two diastereomers (Scheme 17) [110]. 

Fenestranes are compounds of theoretical interest in which the central carbon atom undergoes severe planarization distortion. Reactions sequences involving double intramolecular Pauson-Khand reactions of ene-diynes, or intramolecular Pauson-Khand of dienynes followed by photochemical [2 + 2] cycloaddition, successfully lead to [5.5.5.5]- or [4.5.5.5]fenestrane, respectively [42], For instance, compound 37 was obtained from ene-diyne 36 in moderate yield as a single all-czs stereoisomer [43] (Scheme 18). 

Other donble bonds on the alkenyl chain can trap the initial gold carbenes leading to cyclopropanes. Thus by using An(I) catalysts, dienynes in eqnations (67) and (68) undergo totally stereoselective cyclizations to yield tetracyclic compounds under milder conditions s n than those required with other metal catalysts. ... 

In this account, an overview of the methods employed for the synthesis of conjugated dienes and polyenes is presented. Dienes and polyenes with isolated double bonds are excluded, as they are accessed through methods usually employed for alkene synthesis. Oligomerizations and polymerization reactions leading to polyenes are also not covered. Synthesis of 1,2-dienes, i.e. allenes, is excluded from the purview as there is a volume in the present series devoted to this functional group. Synthesis of heterodienes, conjugated enol ethers, [n]-annulenes and related compounds are also not covered here. However, enynes, dienynes and enediynes syntheses have been included in a few cases in view of their emerging importance. 

The synthesis of bis-aryloxo titanacyclopent-2-ene and titanacyclohept-3-ene (Scheme 93) derivatives has been reported via tricyclization of dienynes. The molecular structure of the titanacyclohept-3-ene has been determined by X-ray diffraction. It is suggested that the formation of the titanacyclohept-3-ene compound proceeds through an insertion of olefin into the Ti-vinyl bond of a titanacyclopent-2-ene intermediate. The metallacycles show interesting reactivity and synthetic usefulness and form novel organic molecules by hydrolysis and thermal catalysis.178... 

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