Triynes

The intermediate in this double 1,6-elimination may be the pentaene C1-CH=C=C=C=C=CH2, routes via other highly unsaturated compounds cannot be ruled out. Since the elimination is a very clean reaction, prior isolation of the explosive triyne is not always necessary 2-ethynylselenophen, for example, can... 

The terminal diyne 320 is prepared by coupling of the zinc acetylide 318 with /rfln.s-l-iodo-2-chloroethylenc (319), followed by elimination of HCI with sodium amide[231]. Similarly, terminal di- and triynes are prepared by using cw-l,2-dichloroethylene[232]. The 1-alkenyl or l-aryl-2-(perefluoroalkyl) acetylene 321 is prepared by the reaction of a zinc acetylide with halides[233]. 

The cyclization of the enediynes 110 in AcOH gives the cyclohexadiene derivative 114. The reaction starts by the insertion of the triple bond into Pd—H to give 111, followed by tandem insertion of the triple bond and two double bonds to yield the triene system 113, which is cyclized to give the cyclohexadiene system 114. Another possibility is the direct formation of 114 from 112 by endo-rype. insertion of an exo-methylene double bond[53]. The appropriately structured triyne 115 undergoes Pd-catalyzed cyclization to form an aromatic ring 116 in boiling MeCN, by repeating the intramolecular insertion three times. In this cyclization too, addition of AcOH (5 mol%) is essential to start the reaction[54]. 

Diynes and triynes refer to alkynes containing two or three triple bonds poly-ynes contain multiple triple bonds. A conjugated triyne is a straight-chain hydrocarbon with triple bonds alternating with single bonds. An examples is... 

Compounds with more than one triple bond are called diyne.s, triynes, and so forth compounds containing both double and triple bonds are called enynes (not ynenes). Numbering of an enyne chain starts from the end nearer the first multiple bond, whether double or triple. When there is a choice in numbering, double bonds receive lower numbers than triple bonds. For example ... 

Notice that an is used to indicate the absence of a double bond or triple bond, such as in pentane above. If there are two double bonds in a compound, then the unsaturation is -dien-. Three double bonds is -trien-. Similarly, two triple bonds is -diyn-, and three triple bonds is -triyn-. For multiple double and triple bonds, we use the following terms ... 

In contrast to the series of hydrocarbons, heterocyclic analogues, even of cyclonona-l,4,7-triyne 2 (u = 3), are known. This is because heteroatom linkers more easily adopt smaller bonding angles and thereby provide some relief of overall angle strain. Since heteroatoms have different electronic properties to carbon atoms, the perceived homoconjugative and homoaromatic effects might be expressed more pronouncedly in heterocyclic [n]pericyclines. 

In order to minimize the formation of side products, PAM 4 can be assembled via an intramolecular approach [23]. The Sonogashira protocol [15] and conversion of masked iodides [24] comprises most of the chemistry involved in Scheme 7. Using these proven methods, diyne 16 and subsequently triyne 17 can be prepared quickly. lodination, desilylation, and intramolecular alkynylation with Pd(dba)2 under high dilution conditions furnished 4 as the sole product. 

An alternative mode for dehydrobenzoannulene decomposition was recently reported by Vollhardt et al. [58]. Non-planar hybrid 81, prepared in low yield via cyclodimerization of known triyne 82 [Eq.(3)], reacted explosively at ca. 250°C to give a nearly pure carbon residue. Solvent extraction of the black powder failed to yield soluble materials such as fullerenes however, analysis of the residue by TEM showed formation of bucky onions and bucky tubes [59], in addition... 

As complex 40 proved to be active in cycloaddition reactions and is isoelectronic to Rh(+1), which is a potent catalyst for [2 + 2 + 2] cycloadditions [20, 21], it was expected that 40 might also be active in those reactions, which is indeed the case. Triyne 54 could be converted to the [2 + 2 + 2]-cycloaddition product 55 in good yield (eq. 3 in Scheme 11). Mechanistically, this reaction is also assumed to proceed via a metallacyclic intermediate. 

Cycloaddition of aUcynes catalysed by transition metals is one of the most efficient and valuable ways to prepare benzene and pyridine systems [12], Among the possible catalytic systems able to catalyse this reaction, cobalt and iron complexes containing NHCs as ligands have shown high catalytic activity in the intramolecular cyclotrimerisation of triynes 36 (Scheme 5.10) [13]. The reaction was catalysed with low loading of a combination of zinc powder and CoC or FeClj with two or three equivalents of IPr carbene, respectively. 

Occurring Acetylene Compounds. XXVII. The Synthesis of a Mixture of Trideca-1.3,1l-triene-5,7,9-triyne (II) and trans-l-Phenylhepta-l,3-diyn-5-ene (V). A Novel Cyclisation Reaction. Acta Chem. Scand. 13, 2101 (1959). 

The Isolation of l-Acetoxy-n-Trideca-2 10 12-triene-4 6 8-triyne from Carlina vulgaris L. Acta Chem. Scand. 8, 1763 (1954). 

Phenylhepta-1,3, S-triyne from Coreopsis grandiflora, Hogg ex Sweet. Acta Chem. Scand. 12, 765 (1958). 

As shown in the two examples described here, formation of the benzene nucleus by trimerization of alkynes is usually catalyzed by a Co-complex. However, Und-heim and coworkers [276] have recently shown that a Ru "-complex can also be used. Reaction of the triyne 6/4-9, which was prepared from SchollkopPs bislactim ether 6/4-8 [277] with Grubbs I catalyst 6/3-13, led to 6/4-10 in an excellent yield of 90%. Hydrolysis of 6/4-10 gave the desired as-indacene-bridged bis(a-amino acid) derivative 6/4-11 (Scheme 6/4.3). 

The reaction of triallylborane with silicon triyne 123 is interesting. A113B attacks both internal and external triple bonds giving rise to silole 124 and two heterocycles with bridgehead boron 125 and 126 in a 1 3 3 ratio as a result of competitive sequential reactions (Scheme 52). When 1,1-allylboration of the internal C C bond followed by intramolecular 1,1-vinyIboration takes place, the silole 124 is formed, while in another case 1,1-allylboration followed by a series of intramolecular 1,2-allylboration reactions leads to boron derivatives 125 and 126 <2002JOM(657)146>. 

In 2003, Efskind and Undheim reported dienyne and triyne domino RCMs of appropriately functionalized substrates with Grubbs type II or I catalysts (Scheme 6.71, reactions a and b, respectively) [151]. While the thermal processes (toluene, 85 °C) required multiple addition of fresh catalyst (3 x 10 mol%) over a period of 9 h to furnish a 92% yield of product, microwave irradiation for 10 min at 160 °C (5 mol% catalyst, toluene) led to full conversion. The authors ascribe the dramatic rate enhancement to rapid and uniform heating of the reaction mixture and increased catalyst lifetime through the elimination of wall effects. In some instances, use of the Grubbs I catalyst was more efficient than use of the more common Grubbs II equivalent. 

Scheme 6.71 Dienyne (reaction a) and triyne (reaction b) domino ring-closing metathesis reactions.

Trisila[l.l.l]orthocyclophane (46) was prepared by the reaction of 3,3,6,6,9,9-hexamethyl-3,6,9-trisilacyclonona-l,4,7-triyne and a-pyrone. The structure of 46 determined by X-ray crystallographic analysis (Fig. 28) indicates a twisted saddle conformation (10). 

Extensively developed by Ojima and co-workers, SiCaT and carbonylative silylcarbocyclization (CO-SiCaC) represent a rapid entry into polycyclic molecules of interest.271 For instance, the rhodium-catalyzed intramolecular SiCaT of triyne 441 afforded tricyclic compound 442 in high yield, accompanied by a small amount of cycloadduct 443 (Scheme 111).270... 

The corresponding permethylzirconocene moiety is complexed by triynes RC = C—C = C—C=CR through two triple bonds in a refashion and complex 107 is obtained. Detailed NMR investigations have revealed a sliding of the permethylzirconocene along the triyne backbone 108 [55], This result is important because it shows there to be a lot of species in the mixture this is the reason for the low selectivity in some reactions. 

Figure 10.16. Different complexation modes of triynes and sliding" along the triyne backbone.

A variety of palladium-catalyzed dimerizations of conjugated enynes and their additions to diynes and triynes gave rise to styrene and phenylacetylene derivatives, respectively. Inter alia, 1,2,4-cyclohexatrienes have been invoked as intermediates in these reactions [134], 5,6-Diphenyl-l,2,4-cyclohexatriene has been proposed as an intermediate in the rearrangement of 4,4-diphenylcyclohexa-2,5-dienylidene to o-ter-phenyl and its possible existence was supported by quantum-chemical calculations [135],... 

Before leaving the diacetylenes we must note some of the stereochemical varieties available in their polymers. Triynes, 138, also polymerize in the crystal by 1,4-addition (213). Also, cyclic di- and polyenes give polymeric products on irradiation. The exact structure of the polymer, however, has been established only in the polymer 135. Note that alternate side chains in this polymer are on opposite sides of the plane of the main chain the polymer is thus meso. However, in principle such a reaction could give rise to optically active polymers in suitable structures. The cyclic tetradiyne 139 crystallizes in a polymerizable phase containing interstitial chloroform (209). The polymerization reaction, which involves... 

Nitrophenylpropiolic acid, 3113 2-Nonen-4,6,8-triyn-l-al, 3112 Octacarbondioxide pentamer, 3904 Octacarbondioxide tetramer, 3884 Octatetrayne-l,8-dicarboxylic acid, 3235 Oligo(octacarbondioxide), 3108 1,3-Pentadiyne, 1825 2-Penten-4-yn-3-ol, 1879 Phenoxyacetylene, 2920... 

Dimethyl-l-butyne, 2408 1,8-Diphenyloctatetrayne, 3788 Hepta-l,3,5-triyne, 2641 l-Heptene-4,6-diyne, 2707... 

Bromoacetylene, 0651 Bromochloroacetylene, 0578 l-Bromo-l,2-cyclotridecadien-4,8,10-triyne, 3599 f 3-Bromopropyne, 1090... 

The intramolecular thermal cyclotrimerization of dodeca-1,6,11-triyne (110) at 450-600 °C afforded l,2,3,6,7,8-hexahydro[a5]indacene (112) and dehydro derivatives. An exothermic cycloaromatization mechanism has been proposed. An initial formation of a single bond gives diradical (111) which is then trapped by an alkyne. °... 

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