Bonds, conjugated triple

Among the appHcations of lower valent titanium, the McMurry reaction, which involves the reductive coupling of carbonyl compounds to produce alkenes, is the most weU known. An excellent review of lower valent titanium reactions is available (195). Titanium(II)-based technology is less well known. A titanium(II)-based complex has been used to mediate a stetio- and regio-specific reduction of isolated conjugated triple bonds to the corresponding polyenes (196). 

Enynes. In the presence of this Pd(II) catalyst, vinyl iodides couple with alkynyltrimethylstannanes with retention of the geometry of the vinyl iodide to provide 1,3-enynes in high yields.2 Since the conjugated triple bond can be reduced to a (Z)-double bond stereospecifically, the coupling also provides a route to (Z,E)-or(Z,Z)-l,3-dienes. An example is the synthesis of bombykol (1), the sex attractant of the silkworm moth. 

Lithium aluminum hydride reduces acetylenic acids containing conjugated triple bonds to olefinic alcohols. Acetylenedicarboxylic acid gave, at room temperature after 16 hours, 84% yield of /ra s-2-butene-l,4-diol [975]. 

Wegner G. Topochemical reactions of monomers with conjugated triple bonds. VI. Topochemical polymerization of monomers with conjugated triple bonds. Makromol Chem 1972 154 35-48. 

Isano Oil. Isano oil, a conjugated triple-bonded glyceride, when heated1 sufficiently, reacts exothermically with violence. Its uses chem reactions are described... 

Due to cooperating anisotropic effects, shieldings of central sp carbon atoms increase with the number of conjugated triple bonds in polyalkynes (Table 4.14). 

When two double bonds lie on either side of a single bond, the double bonds are said to be conjugated. This can occur in a number of different types of molecule, giving rise to such groups as conjugated aldehydes, or the conjugated triple bond of a nitrile ... 

The conjugation of a double bond with a carbonyl group, C O, such as in an aldehyde, can have the serious adverse effect of greatly increasing the likelihood of the material being a severe skin irritant or sensitizer. Examples of this type of influence occur in citral, cinnamic aldehyde, and trans-2 hexenal, as well as in methyl heptine carbonate which has a conjugated triple bond. Benzylidene acetone, which is closely related in structure to cinnamic aldehyde, can no longer be used as a perfumery material for this reason, and the level at which other potential sensitizers can be used in perfume formulations is restricted (see pp. 183-185). 

Additions to conjugated triple bonds occur with facility. Thus, base-catalyzed addition of benzoin to dimethyl acetylenedicarboxylate provides a route to furans (186 187 X = 0), while pyrroles and thiophenes result from an analogous addition of -amino ketones (186 187 X = NH) and -mercapto ketones (186 187 X=S), respectively (Scheme 104) <1964JA107>. 

Butadiyne is a stronger acid than acetylene as might be anticipated on the basis of enhanced electronegativity of j/>-hybridized carbon . As can be seen from Table 1, the dissociation of carboxylic acids is greatly enhanced by a triple bond in the a, p position, and is increased further by a second conjugated triple bond, but to a smaller extent. A third triple bond has a still smaller acid-strengthening effect- . 

By the use of di-secondary glycols it is possible to obtain disubstituted polyynes with greater numbers of conjugated triple bonds. The classical work of Bohlmann on the synthesis of di-/-butylpolyynes involved extensive use of this approach as illustrated in Scheme 5 for the heptayne 81. In this case the much milder base sodium... 

As the number of conjugated triple bonds is increased, an increase in reactivity toward nucleophiles is observed. The reactivity of 2,4,6-octatriyne (102, n = 3) toward methanol addition, which gives 104, is somewhat greater than that of 2,4-hexadiync, but a very large increase is noted for 2,4,6,8-decatetrayne (102, n = 4). The product 105 from the addition to (102, n = 4) is a mixture of cis-trans isomers,... 

Simple alkynes are not reduced by lithium aluminium hydride at a significant rate, but polyynes with four or more conjugated triple bonds react readily under mild conditions. Thus, the tetrayne 216 is reduced at room temperature within a few... 

Certain diacetylene derivatives undergo a remarkable polymerization reaction in the solid state under the influence of heat, ultraviolet light. X-rays or y radiation - . The reaction involves 1,4-addition of the conjugated triple bonds and produces a... 

The spectra show four broad but clear signals at 40, 45-70 (centered at 60), 85-95, and 125-135 ppm attributable to saturated (sp ) carbon atoms bearing residual chlorine, polyyne sequences, isolated or carbonyl-conjugated triple bonds, and polyene structures, respectively. 

The topochemical polymerization of monomers with conjugated triple bonds is an interesting example of the relationship between packing properties and reactivity in the solid state. For solid state polymer-izability the monomer molecules must be arranged in a herringbone-like structure according to Figure 1 so that only one nearest distance between the triple bonds of adjacent molecules of 3 to 4 A is affected. To... 

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