Divalent vinyl ketones derived from fluorene: a facile synthesis of bifunctional acrylic monomers with high reactivity in thia-/aza-Michael addition and Morita-Baylis-Hillman reactions

Abstract

Although vinyl ketones (VKs) exhibit excellent reactivity toward radicals and nucleophiles, their application in polymer chemistry has been limited compared with that of acrylates. One of the reasons is the difficulty of the synthesis, particularly that of multivalent VKs. Herein, we report the facile synthesis of divalent VKs via Friedel‒Crafts acylation of fluorene and subsequent elimination reactions. For example, via this approach, 2,7-diacryloyl-9,9-dimethylfluorene was obtained at high yields (78%). Because the monomer was obtained at high purity through recrystallization and washing, the procedure is suitable for industrial applications. The addition of dithiols and diamines via thia- and aza-Michael addition afforded the corresponding polythioesters and polyamines, respectively. In addition, the divalent VKs exhibited high reactivity in the Morita‒Baylis‒Hillman reaction with formaldehyde, affording a diol monomer. The polycondensation of the diol monomer and isophthaloyl dichloride yielded a poly(conjugated-ketone ester). Consequently, the divalent VKs described herein are attractive monomers and monomer precursors with ready accessibility and sufficient electrophilicity. A series of divalent vinyl ketones containing fluorene backbone were synthesized via Friedel-Crafts acylation and subsequent elimination reactions. The divalent vinyl ketones underwent polyaddition with dithiols to yield the corresponding polysulfide via thiol–ene click chemistry. They also exhibited high reactivity in the Baylis-Hillman reaction with formaldehyde to afford a diol monomer, and the polycondensation with isophthaloyl dichloride yielded a poly(conjugated-ketone ester).