1,6-Heptadiyne

The polymers which have stimulated the greatest interest are the polyacetylenes, poly-p-phenylene, poly(p-phenylene sulphide), polypyrrole and poly-1,6-heptadiyne. The mechanisms by which they function are not fully understood, and the materials available to date are still inferior, in terms of conductivity, to most metal conductors. If, however, the differences in density are taken into account, the polymers become comparable with some of the moderately conductive metals. Unfortunately, most of these polymers also have other disadvantages such as improcessability, poor mechanical strength, instability of the doped materials, sensitivity to oxygen, poor storage stability leading to a loss in conductivity, and poor stability in the presence of electrolytes. Whilst many industrial companies have been active in their development (including Allied, BSASF, IBM and Rohm and Haas,) they have to date remained as developmental products. For a further discussion see Chapter 31. 

Heptatetraene (diallenylmethane) (30) is produced in 1% yield in the base-catalyzed isomerization of 1,6-heptadiyne (243 see below). Its preparation from the bisdibromocarbene adduct 238 to 1,4-pentadiene (237) failed rather than 30, its isomerization product 239, a derivative of 12, was isolated [95] in poor yield and was accompanied by 1- and 6-methylfulvene, respectively [96]. 

The dienyne 33 is produced by base-catalyzed isomerization of 1,6-heptadiyne (243) [98] in a mixture with other C7Hg hydrocarbons, among them traces of dialle-nylmethane (30). The still higher homolog 1,2,7,8-nonatetraene has also been described [99]. 

Itoh and coworkers111 carried out tandem [2 + 2 + 2]/[4 + 2] cycloadditions catalyzed by a ruthenium catalyst. The reaction of diyne 147 with excess norbomene 148 in the presence of ruthenium catalyst 153, for example, afforded 149. Adduct 150 either dissociated from the catalyst or reacted with another equivalent of norbornene. In the latter case, a ruthenium catalyzed Diels-Alder reaction occurred, affording hexacyclic adduct 152 via 151 (equation 43). Compounds 150 and 152 were obtained in yields of 78% and 10%, respectively. Both cycloaddition reactions proceeded with complete stereoselectivity. When 1,6-heptadiyne was used instead of 147, only trace amounts of a cycloadduct were obtained. Replacing norbornene by norbornadiene, which was expected to result in polymer formation, did not afford any adduct at all. 

In the presence of excess nitrile, a second ring closure takes place at the cobalt and leads to derivatives of tetrahydroisoquinoline ( 1) in —60% yield. Compound (22) is obtained analogously from 1,6-heptadiyne. 

The catalytic cyclocarbonylations of diynes proceed efficiently to afford fused cyclohexadienes via trapping of the ruthenacyclopentadiene intermediate by an alkene component <2000JA4310>. Thus, the ruthenium-catalyzed cyclo-co-trimerization of 1,6-heptadiyne derivatives possessing a heteroatom at the 4-position affords heterotricycles in good yields (Equation 110). 

Tanaka and have independently developed effective protocols for the catalytic cyclization/borylsilylation of diynes to form bis(functionalized) dialkylidene cyclopentanes. As an example of the Tanaka procedure, reaction of 1,6-heptadiyne with borylsilane 99 catalyzed by a 1 2 mixture of Pd2(DBA)3 and ETPO (ETPO = 4-ethyl-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octane) at 110°G for 2h gave 100 in 81% yield (Equation (64)). As an example of the Ito procedure, reaction of 1,7-octadiyne with dimethylphenylsilylpinacolborane, catalyzed by the Ni(0) complex generated in situ from a 1 2 2 mixture of Ni(acac)2, DIBAL-H, and P(/ -Bu)3 in toluene at 110°C, gave the bis(functionalized) dialkylidene cyclohexane 101 in 55% yield (Equation (65)). " Tanaka s protocol was also effective for the cyclization/borylsilylation of 1,6-enynes. As an example, reaction of dimethyl allylpropargylmalonate with 99 catalyzed by Pd2(DBA)3/ETPO gave the bis(functionalized) alkylidene cyclopentane 102 in 84% yield with exclusive delivery of the borane to the alkyne moiety of the enyne (Equation (66)). ... 

A number of Mo carbene catalysts, bearing various modified ligands, have been reported and proven to elegantly induce living polymerization of acetylene monomers. The first example is the cyclopolymerization of 1,6-heptadiynes catalyzed by Mo carbenes Mo carbenes ligated by bulky imido and alkoxy groups are quite effective. In... 

The reaction with 1,6-heptadiyne gives cyclopropylphenol, presumably via insertion-intramolecular-cycloaddition steps. Again, the cyclopropyl ring is retained (equation 82)140. 

Although the polymerization of diene monomers is most familiar for 1,3-dienes, as in the production of rubbers, the polymerization of 1,6-dienes to yield polymers containing six-membered rings ( cyclopolymerization ) has been well established for many years43. Gibson et al.441 have used cyclopolymerization of 1,6-diynes to prepare polymers which are effectively substituted polyacetylenes, the archetype being the polymerization of 1,6-heptadiyne ... 

Another type of bicyclo[3.3.0]octadienone formation is observed in the reactions of 4,4-gem-disubstituted 1,6-heptadiynes (353) with HSiMe2Bu-t catalyzed by Rh(acac)(CO)2 or Rh2Co2(CO)i2 under forced conditions, i.e. at 120 °C and 50 atm of CO, affording 7,7-disubstituted bicyclo[3.3.0]octa-l,5-dien-3-ones (354) in 71-95% isolated yields (equation 143)340,341. 

Furthermore, a four-component cycloaddition reaction (7]6-thiepine I,l-dioxide)tricarbonylchromium(0) 52 with tethered diynes under photoactivation afforded pentacyclic adducts formally derived from a sequential [671+271]/ [67l+27t]/[2(T+27i] cycloaddition process <1999OL507>. Photocycloaddition of the complex 52 with excess 1,7-octadiyne 66a or 1,8-nonadiyne 66b (C1CH2CH2C1, hv (Pyrex filter)) afforded the pentacyclic triene sulfones 67a and 67b in 45% and 38% yields, respectively (Equation 4). In contrast, 1,6-heptadiyne 66c afforded only the three-component cycloadduct 68 in 56% yield (Equation 5). 

Cycloadditions. This rhodium complex effects trimerization of a 1,6-heptadiyne with a terminal alkyne to form a benzene derivative (equation I). The paper reports one example of an intramolecular [2 + 2 + 2]cycloaddition (equation II). 

Cyclization of triynes to benzenes,4 Wilkinson s catalyst catalyzes [2 + 2+2]cycloaddition of 1,6-heptadiynes with monoynes to form substituted benzenes. Intramolecular [2+2 + 2]cycloaddition of triynes is also possible with this catalyst. 

Strategies to pyridines include a ruthenium-mediated [2+2+2] cycloaddition to produce annulated products <20010L2117>. Reaction of 1,6-heptadiynes with electron-deficient nitriles yields the pyridine (Equation 175), whereas the same strategy using isocyanates leads to the 2-pyridone (Equation 176). 

The cyclohomopolymerisation of 1,6-heptadiyne by using Shirakawa [85] and related [86] catalysts is a representative insertion polymerisation of acetylenic monomers with Ziegler-Natta catalysts ... 

Cyclopolymerisation of 1,6-heptadiyne derivatives has also been carried out in the presence of Pd-based catalysts [87-89]. 

The cyclopolymerisation of a, co-diacetylenes with metathesis catalysts concerns 1,6-heptadiyne and its 4,4-disubstituted derivatives [87, 106, 154-163] and 1,7-octadiyne [164]. 

The cyclopolymerisation of 1,6-heptadiyne derivatives such as diethyl dipro-pargyl malonate by a Schrock carbene, [Me(CF3)2CO]2Mo(=NAr)=CHMe3, via a metathesis mechanism, proceeds in a living fashion to provide a conjugated polymer having both five-and six-membered rings, which is shown schematically below [154, 155] ... 

The living nature of the discussed cyclopolymerisation of the 1,6-heptadiyne derivative in the presence of Schrock carbene as the catalyst has been demonstrated by the synthesis of a block copolymer with 2,3,-dicarbomethoxynor-bornadiene [25]. 

Give reasons why the cyclopolymerisation of a, co-dialkyne such as 1,6-heptadiyne proceeds via both five-membered and six-membered ring closure. 

The reaction of 1,6-heptadiynes with alkenes led to a [2+2+2] cyclotrimer-ization in the case of cyclic or linear alkenes possessing heteroatoms at the al-lylic position. Bicyclic cyclohexadienes were thus produced in good yields with RuCl(COD)C5Me5 [92,93] (Eq. 71). A ruthenacyclopentadiene is invoked as an intermediate in the mechanism. Insertion of the alkene becomes possible by a heteroatom-assisted reaction. 

We have found that a combination of intermolecular and intramolecular domino enyne metathesis reactions is also feasible [122]. Reaction between 1,6-heptadiynes 69-72 and allyltrimethylsilane promoted by 2 gave triene cycloadducts 73-76 in moderate-to-good yields (Scheme 22). 

Abstract Metathesis-based polymerizations of 1-alkynes and cyclopolymerizations of 1,6-heptadiynes using late transition metal catalysts are reviewed. Results obtained with both binary, ternary, and quaternary catalytic systems and well-defined molybdenum- and ruthenium-based catalysts are presented. Special consideration is given to advancements in catalyst design and mechanistic understanding that have been made in this area over the last few years advancements that have facilitated tailor-made syntheses of poly(ene)s. In addition, the first supported ruthenium-based cyclopolymerization-active systems are summarized. Finally, selected structure-dependent properties will be outlined where applicable. 

The cyclopolymerization of 1,6-heptadiynes represents a powerful alternative to 1-alkyne polymerization [81, 94]. Cyclopolymerizations may be accom-... 

In terms of polymer structure, cyclopolymerizations of 1,6-heptadiynes usually yield poly(ene)s that contain a mixture of five- and six-membered rings (Fig. 6). 

Fig. 6 Possible ring structures of poly( 1,6-heptadiynes) prepared via cyclopolymerization. Poly(cyclopent-l-enylene-l-vinylene)s (A) poly(cyclohex-l-ene-3-methylidene)s (B) and mixed structures (C)...

In order to understand the polymer structures that are obtained in the polymerization of 1,6-heptadiynes, one needs to consider all possible polymerization mechanisms. If 1,6-hep tadiynes are subject to cyclopolymerization using well-defined Schrock catalysts, polymerization can proceed via two mechanisms. One is based on monomer insertion, where the first alkyne group adds to the molybdenum alkylidene forming a disubstituted alkylidene, which then reacts with the second terminal alkyne group to form poly(ene)s consisting of five-membered rings. Analogous to 1-alkyne polymerization, one refers to this type of insertion as a-insertion (Scheme 4). 

Scheme 4 Two possible reaction pathways and resulting ring structures in the cyclopolymerization of 1,6-heptadiynes...

The C-NMR spectrum of poly(4-(ethoxycarbonyl)-4-(lS,2R,5S)-(+)-men-thoxycarbonyl-1,6-heptadiyne) indicates a polymer containing almost solely five-membered rings (Fig. 10). In addition, only one single set for each type of carbon was observed, indicative of a highly tactic base. Keeping the symmetry restrictions described above in mind, either a cis or trans-st structure can be assigned. 

While classical catalysts usually result in ill-controlled polymerization systems, well-defined Schrock initiators cyclopolymerize 1,6-heptadiynes in a living manner - in most cases a class VI living manner (according to Matyjaszewski [84]). Polymers based on one single repetitive unit (poly(cyclopent-l-enylene-... 

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