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]

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Summary

Introduction

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).

Results
Conclusion

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