Ionic porous organic polymer (IPOP) based on twisted biphenyl Scaffold: Green and efficient heterogeneous catalytic synthesis of β-Arylthioketones and biscoumarins

Abstract

A new viologen-based ionic porous organic polymer (IPOP) has been developed based on a twisted biaryl (TMBB) as the monomer and Menshutkin reaction as the polymerization reaction. IPOP is thermally stable and insoluble in H2O and common organic solvents (MeOH, MeCN, EtOH, DCM, etc.). The presence of cationic sites as well as counter bromide anions in the polymeric matrix endow the IPOP with properties akin to those of the phase-transfer quaternary ammonium salt, namely TBAB, to permit its application as a recyclable heterogeneous catalyst for organic transformations. It’s shown that IPOP can be readily applied as a phase-transfer catalyst for Michael addition of thiols to α,β-unsaturated carbonyl compounds, providing access to organosulfur compounds, namely, β-arylthioketones, in excellent isolated yields. In a similar manner, IPOP is shown to be applicable as a recyclable heterogeneous catalyst for facile synthesis of biscoumarins, which are an important class of molecular systems exhibiting a variety of biological activities such as anti-coagulant, anti-anthelmintic, anti-HIV, anti-bacterial, anti-oxidant, anti-cancer, etc. Thus, a novel, efficient and ecofriendly approach in a manner mimicking the phase-transfer quaternary ammonium salts has been developed for the synthesis of β-arylthioketones and biscoumarins; the IPOP can be employed as a heterogeneous catalyst for at least 10 catalytic cycles without any loss of catalytic activity.