Dienes-conj ugated

Conj ugated Ladder Polymers. Since the 1930s double-stranded, ladder-type polymers have been prepared in a multistep process with limited success of cyclization (191,192). Other routes have also been explored such as those for poly(acrylonitrile) (193,194), poly(l,2-butadiene), poly(3,4-isoprene) (195), or poly(butadiyne)s (196). These materials were found to be poorly soluble and unworkable, with a considerable number of defects in the structure (incomplete cyclization, cross-linking, radical sites). The first successful synthesis of a ladder polymer with a completely defined structure was accomplished in 1991 by Sherf and Mullen (197). The first step was the AA/BB-t5q)e polycondensation of an aromatic diboronic acid with a substituted 2,5-dibromo-l,4-dibenzoylbenzene to give a single-stranded precursor PPP-type polymer, followed by cyclization to the ladder structure (Fig. 8). Several other examples exist that have resulted in ladder-type structures. These include angular polyacene (198,199), Diels-Alder polyaddition of AB-type diene-dienophiles (200), AA/BB-type Diels-Alder polyaddition of a bisdiene and a bisdienophile (201), thienylene imits (202),... 

The Chemical Consequences of Conjugation Addition Reactions of Conj ugated Dienes... 

TelomerizatiorL Conj ugated dienes combine with nucleophiles such as water, amines, alcohols, enamines and stabilized carban-ions in the presence of palladium acetate and triphenylphosphine to produce dimers with incorporation of one equivalent of the nucleophile. Telomerization of butadiene (eq 7) yields linear 1,6- and 1,7-dienes and has been used for the synthesis of a variety of naturally occurring materials. ... 

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