Abstract
Cyclobutenedione is an aromatic ring that exhibits strong electron-withdrawing properties but is susceptible to undesired reactions with nucleophiles. Herein, Kumada–Tamao–Corriu coupling polymerization of a cyclobutenedione monomer whose carbonyl groups are protected as acetals was achieved. Hydrolysis of the acetals afforded donor–acceptor type π-conjugated polymers consisting of cyclobutenedione as an acceptor unit and bithiophene as a donor unit. The acetal-protected monomer was also subjected to Suzuki–Miyaura coupling polymerization. The absorption and emission spectra of the deprotected polymers shifted to the longer wavelength compared with the acetal-protected polymers.
Highlights
Cyclobutenedione is a four-membered aromatic ring with two carbonyl groups that render this unit strongly electronwithdrawing
In the eld of polymer chemistry, the synthesis of polysquaramide is commonly achieved by polycondensation of squaric acids or squaric acid diesters and diamines.[8]
The reactions between squaric acid diesters and amines proceed under mild conditions.1,2d the synthesis of pconjugated cyclobutenedione polymers has been reported by Suh's group, who synthesized cyclobutenedione-containing poly(phenylenevinylene)s by dehalogenation polycondensation and Heck coupling polymerization.[9]
Summary
Cyclobutenedione is a four-membered aromatic ring with two carbonyl groups that render this unit strongly electronwithdrawing. The previously reported conditions of Suzuki–Miyaura coupling reaction between acyl chloride and arylboronic acid were used.[18] First, reaction of 1a and 2a was performed in the presence of 1.0 mol% of Pd(OAc)[2] and 3.4 equivalents of Na2CO3 in H2O/ PEG-2000 at 60 C.18a The 1H NMR spectrum of the crude product revealed that 1a was hydrolyzed (Table 1, entry 1).
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