17 Azulene-Based Materials for Organic Field-Effect Transistors
349
17.4.2 Synthesizing Terazulene Isomers
The Suzuki–Miyaura cross-coupling reaction was used to construct the azulene
backbone (Scheme 17.3). The coupling substrates, namely 2-azulenylboronic
acid ester [27], 6-bromoazulene [28], and 6-azulenylboronic acid ester [29],
are known compounds and were synthesized from ethyl 2-aminoazulene-1,3dicarboxylate, itself prepared by the Nozoe–Seto azulene synthesis. Here, the novel
2-chloroazulene-6-boronic acid ester 12, synthesized by the diazotization of the 2aminoazulene-6-boronic acid diester 11 [29], is a key compound used to synthesize
all of the terazulenes and facilitates the sequential introduction of azulene backbone
units based on the difference in reactivities of the 2- and 6-positions. We converted
compound 12 into 2,6
-biazulene (13) and 6,6
-biazulene (14) by Suzuki–Miyaura
cross-coupling reactions, followed by decarboxylation to chlorobiazulenes 15 and
16. The four terazulene isomers were finally prepared by reactions with the corresponding boronic acid esters. All compounds were highly thermally stable and were
purified by sublimation.
Scheme 17.3 Syntheses of terazulene isomers TAz1, TAz2, TAz3, and TAz4
349
17.4.2 Synthesizing Terazulene Isomers
The Suzuki–Miyaura cross-coupling reaction was used to construct the azulene
backbone (Scheme 17.3). The coupling substrates, namely 2-azulenylboronic
acid ester [27], 6-bromoazulene [28], and 6-azulenylboronic acid ester [29],
are known compounds and were synthesized from ethyl 2-aminoazulene-1,3dicarboxylate, itself prepared by the Nozoe–Seto azulene synthesis. Here, the novel
2-chloroazulene-6-boronic acid ester 12, synthesized by the diazotization of the 2aminoazulene-6-boronic acid diester 11 [29], is a key compound used to synthesize
all of the terazulenes and facilitates the sequential introduction of azulene backbone
units based on the difference in reactivities of the 2- and 6-positions. We converted
compound 12 into 2,6
-biazulene (13) and 6,6
-biazulene (14) by Suzuki–Miyaura
cross-coupling reactions, followed by decarboxylation to chlorobiazulenes 15 and
16. The four terazulene isomers were finally prepared by reactions with the corresponding boronic acid esters. All compounds were highly thermally stable and were
purified by sublimation.
Scheme 17.3 Syntheses of terazulene isomers TAz1, TAz2, TAz3, and TAz4