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- Title
Synthetic Attempts towards Polymers with Pentafulvene Structural Units.
- Authors
Zhang, Gengyi; Neuenschwander, Markus
- Abstract
Synthetic attempts towards fully conjugated polymers 9 with pentafulvene-diyl structural units are described. Cationic polymerization of pentafulvenes 1a (R = X = Me) and 1b (R = X = MeS) nearly quantitatively gives polymers 8a and 8b with typical M n and M w values of 38800 and 53750, respectively, for 8a, and 12000 and 35900, respectively, for 8b. Key step of the conversion 8a → 9a ( Scheme 6) is a quantitative bromination 8a → 32a, the structure of 32a being confirmed by analytical data as well as by spectroscopic comparison with model compound 23. Best results in view of two-fold the HBr elimination 32a → 9a are obtained with Et3N, but so far elimination has not been complete. Synthetic sequences are optimized with model compound 21 ( Scheme 4). Here again, bromination 21 → 23 is quantitative, while two-fold HBr elimination 23 → 22 with Et3N proceeds in 51% yield. Dibromide 23 easily undergoes HBr elimination followed by a Br shift to give bromide 29. Contrary to cationic polymerization, anionic polymerization of simple pentafulvenes 1 to 2 (which would be attractive in view of the conjugated polymers 3) is not successful: For pentafulvene 1b (R = X = MeS), the main reaction is Diels- Alder-type dimerization 1b → 15b ( Scheme 2), even under anionic conditions.
- Publication
Helvetica Chimica Acta, 1995, Vol 78, Issue 5, p1091
- ISSN
0018-019X
- Publication type
Article
- DOI
10.1002/hlca.19950780506