2,6-Octadiene cyclization

Nitrodienes undergo intermolecular Diels-Alder reactions with appropriate dienophiles. The resulting nitro compounds can then be cyclized via a nitrile oxide intermediate.49 Thus, the 2-chloroacrylonitrile Diels-Alder adduct of 8-nitro-l,3-octadiene was prepared and cyclized to give (105) as a 3 1 mixture of diastereomers (Scheme 30). The Diels-Alder adduct of dimethyl acetylenedicarboxylate and 8-nitro-l,3-octadiene cyclized exclusively at the conjugated double bond, activated by the ester groups. Similarly, the quinone Diels-Alder adduct (106) cyclized at the conjugated double bond reduction of the conjugated double bond permitted cyclization on the cycloalkenyl double bond. 

Scheme 43 Synthesis of enantiopure ring-substituted 1,2-diaminocyclohexanes by transition metal catalyzed and promoted cyclization of 1,7-octadienes...

Cyclopolymerization of Nonconjugated Dienes. Cyclopolymerization is an addition polymerization that leads to introduction of cyclic structures into the main chain of the polymer. Nonconjugated dienes are the most deeply studied monomers for cyclopolymerization and for cyclocopolymerizations with alkene monomers 66 In general, (substituted and unsubstituted) dienes with double bonds that are linked by less than two or more than four atoms cannot undergo efficient cyclization and result in crosslinked materials.12 In fact, efficient cyclopolymerization processes have been described, for instance, for a,oo-dienes like 1,5-hexadiene, 2-methyl-l,5-hexadiene, 1,6-heptadiene, and 1,7-octadiene,67 73 which lead to formation of homopolymers and copolymers containing methylene-1,3-cycloalkane units. 

A bis-silylated l,2-octadien-7-yne undergoes very clean cyclization with a slight excess of (7/2-propene)Ti(OiPr)2, prepared in situ from Ti(OiPr)4 and iPrMgCl, at -50 °C for 2 h to give a 1,4-diene as a single isomer after hydrolytic workup (Scheme 16.71) [78]- Deuteration of the reaction mixture afforded exclusively the bis-deuter-ated product, confirming the presence of an intermediate titanacycle. This reaction seems to be general for other allenes with diverse substitution patterns. 

Reaction of iodine with non-conjugated dienes has been applied to the synthesis of cyclic compounds100. Although the reactions of 1,5-hexadiene, 1,6-heptadiene and 1,7-octadiene with I2 in CCI4 gave exclusively products arising from addition to the two double bonds, the introduction of dialkyl substituents into the 4-position of 1,6-heptadiene completely changed the reaction course in favor of cyclization (equation 85). 

Mori has reported the nickel-catalyzed cyclization/hydrosilylation of dienals to form protected alkenylcycloalk-anols." For example, reaction of 4-benzyloxymethyl-5,7-octadienal 48a and triethylsilane catalyzed by a 1 2 mixture of Ni(GOD)2 and PPhs in toluene at room temperature gave the silyloxycyclopentane 49a in 70% yield with exclusive formation of the m,//7 //i -diastereomer (Scheme 14). In a similar manner, the 6,8-nonadienal 48b underwent nickel-catalyzed reaction to form silyloxycyclohexane 49b in 71% yield with exclusive formation of the // /i ,// /i -diastereomer, and the 7,9-decadienal 48c underwent reaction to form silyloxycycloheptane 49c in 66% yield with undetermined stereochemistry (Scheme 14). On the basis of related stoichiometric experiments, Mori proposed a mechanism for the nickel-catalyzed cyclization/hydrosilylation of dienals involving initial insertion of the diene moiety into the Ni-H bond of a silylnickel hydride complex to form the (7r-allyl)nickel silyl complex li (Scheme 15). Intramolecular carbometallation followed by O-Si reductive elimination and H-Si oxidative addition would release the silyloxycycloalkane with regeneration of the active silylnickel hydride catalyst. 

An equivalent reaction has been achieved via the treatment of hydroborated bisalkenes with alkaline silver nitrate solution (Table 1.4).22,23 This method has been used to synthesize a number of small and medium-size carbocyclic rings in moderate to good yield. The selectivity for terminal cyclization observed for 1,6-heptadiene and 1,7-octadiene indicates that, in these cases, hydroboration of each of the alkenes occurs independently to yield acyclic boranes. It has, however, been found that both cyclic and acyclic boranes react under these conditions to yield the ring-closed products (Scheme 1.3). 

Natural products containing six-membered rings are ubiquitous, therefore the following set of target molecules are limited to those containing eight-membered rings that would be accessible via [4+4] cycloadditions. Notably, 1,5-cyclo-octadienes 88 can be converted to bicyclo[3.3.0]octanes 201 transannular electrophilic [124] and radical cyclization (Sch. 44) [125]. 

Stereoselective radical cyclization of 1,5-cyclooctadienes. Winkler and Sridar14 have noted transannular effects on the stereochemistry of cyclization of these octadienes (equation I). Thus radical cyclization of cis-1 and of the corresponding ketone (3) is highly frans-selective and is more rrans-selective than that of the monosubstituted diene 5. Cyclization of a 3,8-disubstituted cyclooctene is... 

In an interesting extension, hydromagnesiation of 1,6-heptadiene and 1,7-octadiene is reported, though without full experimental details, to result in cyclization [65] ... 

This contrasts with the cyclization of 2,6-octadiene (where a less-stable secondary cation would be the equivalent intermediate) having the characteristics of concerted protonation-ning formation (Scheme... 

Silyl-4-alkenals undergo cyclization which gives 3-cyclopentenols. When the intermolecular allylation of enones which favors the conjugate addition pathway is applied to l,8-bis(trimethylsilyl)-2,6-octadiene the four stereocenters of the 2 1 adduct emerge in a defined fashion. ... 

Zirconocene metallacycles are invoked as key intermediates in the catalytic cyclomagnesiation of dienes. To probe for the intermediacy of metallacycles, zirconacyclopentane derivative 658 was synthesized from the reaction of Cp2ZrCl2 and 9,9-diallylfluorene in the presence of 2equiv. of BunLi482 (Scheme 154). This structurally characterized zirconacyclopentane is a catalytically competent intermediate for the cyclization of dienes. For example, cyclomagnesiation of 1,7-octadiene occurs smoothly in the presence of 10mol% of 658. 

Enantioselective cyclizations of amino-octadiene with chiral lanthanocene catalysts provide a facile access to (-l-)-coniine with 63% ee after hydrogenolysis of the... 

Abu-Surrah reported the copolymerization of several a, ca-dienes with CO catalyzed by [Pd(dppp)(NCMe)2](BF4)2 [170]. Although copolymerization of 1,5-hexadiene with CO proceeds via complete cyclization of diene monomer, the copolymerization of 1,7-octadiene and l,6-heptadien-4-ol gives copolymers without a ring structure and with pendant vinyl groups. 

Finally, let us consider the by-products of linalool transformation by I3 cinerea. The formation of 3,9-epoxy-p-menth-l-ene (27), the character impact compound of fresh dill herb (14), can be understood by allylic rearrangement of (E)-2,6-dimethyl-2,7-octadiene-1,6-diol (19) to the corresponding hydroxygeraniol (-nerol). This compound is known to undergo cyclization to the epoxy derivative (27) under acidic conditions (15). 

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