Triynes polyynes

In principle the number of triple-bond stretching vibrations for a conjugated polyyne is expected to be the same as the number of triple bonds ". For symmetrical diynes, one mode should be i.r.-active and one Raman-active for symmetrical triynes, one should be i.r.-active and two Raman-active, etc. Because of the low force constant of the single bonds which separate the acetylene units compared to that of a triple bond, the splittings are small, and only with some of the lower polyynes is the anticipated number of absorption bands observed (see Table 7). The intensity of the C C bands in the i.r. increases with the number of triple bonds, and with Ph(C=C)6Ph, for example, it is the strongest band in the spectrum . 

A one-pot synthesis and derivatization of diynes and triynes is reported. The polyyne framework was formed from a dibromoolefm precursor 96 based on a carbenoid rearrangement, and the resulting Li-acetylide is then transmetallated with zinc chloride which then allowed for the divergent preparation of aryl polyynes 97 via Negishi palladium-catalyzed cross-coupling reactions. 

Intramolecular [2+2+2] Cycloaddition of Polyynes Containing a 1,3-Diyne Block The triyne 2.84 readily trimerizes to afford annelated benzenes 2.85 using catalytic amounts of zinc powder, heterocyclic car-bene with isopropyl substituents (IPr in the scheme) and C0CI2 or FeCl3 (Scheme 2.29) [41]. 

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