Diynes 1,3-, cross-metathesis

Fig. 3a,b Typical diyne metathesis reactions ring-closing alkyne metathesis (RCAM, a) diyne cross metathesis (ACM, b)... 

Diynes are also used to perform intermolecular enyne metathesis. With the objective of producing functionalized hetero- and carbocycles, a cascade diyne-alkene cross metathesis leading to five-membered cyclic products has recently been proposed [27] (Scheme 13). 

Scheme 75. Tandem diyne-ene cross-metathesis to yield cyclic trienes via first generation Grubbs catalyst.

Transposition of Ru-carbenoid prior to cross-metathesis is an important feature for the attachment of an allylic ester unit to the terminus of a diyne. ... 

Both catalysts 1 and 2 are effective in promoting cross-metathesis leading to various conjugated dienes from alkenes and alkynes. Chiral 2-(a-acetoxybenzyl)-1,3-butadiene is obtained from (/f)-3-acetoxy-3-phenylpropyne via cross-metathesis with ethylene. - Furthermore, the reaction of 1,6-diynes with alkenes is even more intriguing ... 

Alkyne metathesis is generally restricted to internal alkynes, and is driven to completion by the evolution of gaseous 2-butyne. Representative examples of alkyne cross-metathesis are depicted in Scheme 33, and include (i) dimerization of alkynylbenzoic acid derivative 287, (ii) alkyne cross-metathesis of 289 and bis(trimethylsilyl)acetylene, (iii) cross-metathesis of enyne 291 and various alkynes and metathesis dimerization of 291, and (iv) formation of high molecular weight alkyne-containing polymers through acyclic diyne metathesis (ADIMET) polymerization of acyclic diynes (e.g., 293) " using the molybdenum hexacarbonyl/2-chlorophe-nol system. 

Scheme 33 Representative examples of alkyne cross-metathesis and acyclic diyne metathesis (ADIMET) polymerization.

Daesung Lee of the University of Illinois at Chicago designed Organic Lett. 2008, 70, 257) a clever chain-waUdng cross metathesis, combining 4 and 5 to make 6. The diyne 3 was carried on (57 , 97 , 707 )-Panaxytriol 7. 

The PPEs [14, 35, 36], which are dehydrogenated analogs of the poly(p-phenylene vinylene) s, display desirable optoelectronic properties that have found extensive use as emissive materials [37, 38]. PPE preparation is dominated by the Sonogashira Pd/Cu-catalyzed cross-coupling of aryl haUdes and terminal alkynes [39]. However, polymerizations under these conditions rarely achieve a high molecular weight, and defects such as diyne formation and alkyne crosshnking in the polymer backbone are endemic [14, 40]. Alkyne metathesis was envisioned as a complementary method to PPE synthesis, with much success. 

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