A,w-Diynes

For high-dilution experiments, for example, the cyclization of a,w-diynes, about 4 volumes of ether per volume of reagent solution can be added as entraining solvent without precipitation of the copper salt. A lower reaction temperature results. 

Coupling reactions of non-conjugated a.w-diynes have been systematically classified by Tamao [17]. 

Pd/Cu-catalyzed coupling of 150 with excess of the liberated pentamer 151 affords the polymer supported 17-mer. Directly heating the mixture of 150 and 151 causes a much lower yield, possibly due to decomposition of the a,w-diyne 150 (R = H). Recovery of excess 151 is simply achieved by filtration from the beads, followed by passage through silica gel. Finally, treatment of anchored 152 with acid liberates the free 120-nm long 17-mer 152. ... 

Many papers in the literature have followed the finding by Masuda and coworkers (9). This article covers the literature from the mid-1980s up to mid-2000. As a result of the rapid growth in the area, the chemistry of polymers from acetylene, 1,3-diacetylenes, and Q, < -diacetylenes are excluded (see Polyacetylene Diacetylene and Tbiacetylene Polymers). The first focus is on the polymerization reaction of substituted acetylenes with various transition metal catalysts. The synthesis of functionally designed polyacetylenes is also covered. Readers are encouraged to access other reviews and monographs on polyacetylene (10-14), on 1,3-diacetylenes (15-19), and on a,Previous review articles are also helpful to survey the chemistry of substituted polyacetylenes (10,13,22-29). 

The cycloaddition of unsymmetrical a,w-diynes with 1-alkyne gives two isomers. The control of regioselectivity is a challenging problem. Limited examples of the regioselective cycloaddition of an unsymmetrical a,w-diyne such as 4 with 1-alkyne... 

Both aliphatic and aromatic isocyanates reacted smoothly with a,w-diyne 7 to give 2-pyridone 48 in high yields (Table 5.2). Aliphatic isocyanates were more reactive than aromatic isocyanates. Electron-rich aromatic isocyanate gave the products in higher yield than electron-deficient aromatic isocyanate. 

Axially chiral A/-aryl-2-pyridone 55 was obtained by the reaction of a,w-diyne 7 with o-substituted aryl isocyanate (Scheme 5.19) [34]. BINAP was an efficient ligand for enantioselective cycloaddition to give axial chirality. 

In 2004, Shibata et al. reported on the atrop-selective biaryl synthesis by iridium-catalyzed [2 + 2 + 2] cycloaddition [8], They developed the synthesis of axially chiral 1,4-teraryls 16 with two atropisomeric chiralities by the neutral iridium(I)/Me-Duphos complex-catalyzed enantio- and diastereoselectivitive [2 + 2 + 2] cycloaddition of a,w-diynes 14, possessing ortho-substituted aryl groups at alkyne termini, with functionalized internal monoynes 15 in high yields with excellent enantio- and diastereoselectivity (Scheme 9.6) [8,9],... 

On the other hand, the reactions of internal a,w-diynes 29 with ortho-substituted phenyl isocyanates 30 in the presence of the cationic rhodium(I)/BINAP catalyst furnished enantioenriched A-aryl-2-pyridones 31, having a chiral C—N axis, while the yields and ee values of the products 31 were highly depend on the substituents of a,w-diynes 29 and isocyanates 30 (Scheme 9.34) [30]. 

Most of the general synthetic strategies overcome this limitation by using two components in the synthesis of alkynes (Scheme 2.2) [9]. Although the formation of metallocycles is limited by geometry and entropic component, this intermolecular concept works well for the construction of larger polycyclic systems from simple unsaturated precursors. The development of the intermolecular version of cyclotrimerization of triynes led to the use of a,w-diynes 2.7 as one... 

A very practical and highly regioselective general method for preparing substituted pyridines 2.107 from a,w-diynes 2.105 and alkyl or aryl nitriles 2.106 with variations of functional groups has been developed. The reaction involved the use of 5 mol% of CoCl2-6H20/dppe catalyst in the presence of powdered Zn (10 mol%) at 50°C in N-methylpyrrolidone (Scheme 2.37) [78]. 

Vollhardt and colleagues338b studied the regiochemistry in these cycloaddition reactions. When the a,cu-diynes had large substituents at both termini, the reaction with W-phenylsulfonylindole did not afford any adduct due to steric hindrance. When smaller substituents were present, the cycloaddition proceeded in such a way that the larger substituent was distant from the phenylsulfonamide moiety, as illustrated for the reaction of 585 with 586 (equation 168). Anti 587 and syn 588 were obtained in a 61 39 ratio. 

Homogeneous, single-component catalysts such as, e.g., W(=CCMe3)(OCMe3)3 or W(=CMe)(OCMe2CF3)3, cannot only be used for exchange metathesis of alkynes but also for ROMP of cycloalkynes, ADMET of a,to-diynes, and RCM of a,co-diynes [751]. 

Tricyclic skeletons such as 85, 87, 89 with a central benzene ring are formed in the fully intramolecular Pd-catalyzed cascade cyclization of 2-bromo-l-ene-//,w-diynes 84, 86, 88 and analogs (Scheme 24). This process involves two alkyne relays in a row and a final 67r-electrocyclization or 6-endo-trig carbopalladation with ensuing / -dehydropalladation. 

Among partially intramolecular versions of this cocycloaddition, a,t>>-diynes have been found to cycloadd only with low efficiency to isocyanates in the presence of CpCo precursors. In contrast, w-iso-cyanatoalkynes react smoothly with silylated alkynes in the presence of CpCo(CO)2, giving high yields of products formed with excellent chemoselectivity and modest to excellent regioselectivity (equation 47). The regioselectivity is most likely controlled in a manner similar to that in equation (43). 

Hexa-l,5-diyne in dry ether added dropwise to NaNHg in liq. NH3 under Ng, stirred 3-4 hrs. at - 78°, the cooling bath removed, the NHg allowed to evaporate during 48 hrs. under Ng, traces of NHg removed in a vacuum desiccator, and the solid residue hydrolyzed at 0° with deuterium oxide crude 1,6-dideuterio-hexa-l,5-diyne. Y 76%. B. A. W. Coller, M. L. Heffernan, and A. J. Jones, Australian J. Chem. 27, 1807 (1968). 

There are at least two issues to be addressed regarding the Type lie circular cascade process shown in Scheme 42. One is the regioselectivity in the initial intermolecular carbopalladation. Since it is not very difficult to differentiate the two terminal positions of Q ,(w-diynes, this is not a serious problem in most cases. A more serious problem is the exclusive formation of fulvene derivatives observed in a couple of cases [124] (Scheme 45). It is not very clear what the scope of the fulvene formation is and whether the course of the reaction could be altered to give benzene derivatives. 

The development of Mo and W alkylidene complexes (4), that is, the so-called Schrock carbene, has contributed to the rapid growth of polymerization chemistry of substituted acetylenes. Although the preparation of these catalysts is relatively difficult because of their low stability, in other words, high reactivity, they elegantly act as living polymerization catalysts for substituted acetylenes such as ort/io-substituted PAs and a,(B-diynes. The details of the living polymerization are described below. 

We can narrow the difference from 10 kJmol-1 even further once it is remembered that in the comparison of meso-bisallene, 27, and (Z, Z)-diene, 29, there are two extra alkylallene and alkylolefin interactions for which a stabilization of ca 3 kJ mol-1 for the latter was already suggested. Admittedly, comparison with the corresponding 1,5-cyclooctadiyne suggests strain-derived anomalies. From the enthalpy of hydrogenation, and thus derived enthalpy of formation, of this diyne from W. R. Roth, H. Hopf and C. Horn, Chem. Ber., 127, 1781 (1994), we find 1/2S (bis-allene, bis-acetylene) equals ca — 80 kJ mol-1. We deduce that the discrepancy of this last 5 quantity from the others is due to strain in the cyclic diyne. 

A few mercury complexes featuring diynyl ligands are known. Deprotonation of W =C(NMe2)C=CC=CH (CO)s with BuLi, followed by treatment with HgCl2 has afforded Hg C=CC=CC(NMe2)=W(CO)5 2 and mercury(I) derivatives of more common terminal diynes HC=CC CR (R = Me, Ph) have also been described. ... 

The reaction of two equivalents of W(C=CC=CH)(CO)3Cp with Ru3(CO)io (NCMe)2 gives the RU3W cluster 149 (Scheme 30), which is also obtained from 135 and W(C=CC=CH)(CO)3Cp. The extended organic ligand is formed by coupling of two molecules of the diynyl complex with two of CO, to form a cyclopen-tadienone attached by a carbenic interaction to the cluster W atom, and featuring formylethynyl and C=CW(CO)3Cp substituents. " One of the elementary steps in the reaction mechanism may involve formal rearrangement of the diyne to a dicarbyne. 

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