demanding experiment. The polyalcohols 2b gave better results upon Friedel–Crafts
cyclization than the corresponding polyketones 2a, and the choice of the reagent in
the reductive C–C bond formation to produce 5 appeared crucial. Nevertheless,
defects did occur and failure to form all bridges in 2 had, for example, severe
consequences for the persistence length of the chain [138, 139]. This finding suggests
the obvious conclusion that in polymer synthesis it is not only important to avoid
defects, but also to detect them. It appeared logical then, and this approach has been
pursued since [140, 141] by both our group and that of Schlu ¨ter [142], to target poly
[n]acene structures 20 and to synthesize the required six-membered rings using
Diels–Alder cycloadditions [143–145]. A number of diene and dienophile
components have been utilized (Scheme 5) and the idea has been to benefit from
the perfection of a concerted 4+2 cycloaddition for the precise synthesis of ribbon
structures [146].
Reactions of AA+BB type have mainly been considered with double diene
systems such as 13 and 13a or double dienophiles such as 12 and 15. Even with
Scheme 5 En route to poly[n]acenes
Graphene as a Target for Polymer Synthesis
69
cyclization than the corresponding polyketones 2a, and the choice of the reagent in
the reductive C–C bond formation to produce 5 appeared crucial. Nevertheless,
defects did occur and failure to form all bridges in 2 had, for example, severe
consequences for the persistence length of the chain [138, 139]. This finding suggests
the obvious conclusion that in polymer synthesis it is not only important to avoid
defects, but also to detect them. It appeared logical then, and this approach has been
pursued since [140, 141] by both our group and that of Schlu ¨ter [142], to target poly
[n]acene structures 20 and to synthesize the required six-membered rings using
Diels–Alder cycloadditions [143–145]. A number of diene and dienophile
components have been utilized (Scheme 5) and the idea has been to benefit from
the perfection of a concerted 4+2 cycloaddition for the precise synthesis of ribbon
structures [146].
Reactions of AA+BB type have mainly been considered with double diene
systems such as 13 and 13a or double dienophiles such as 12 and 15. Even with
Scheme 5 En route to poly[n]acenes
Graphene as a Target for Polymer Synthesis
69