Microwave- and Ionic Liquids-Based Sustainable Preparation of
2-Acylbenzothiazoles
Abstract
Microwave irradiation (MW) and ionic liquids (ILs) are two of the most
promising relatively greener synthetic approaches for preparing the
value-added chemicals. The breakthrough of their combination in the
generation of 2-acylbenzothiazoles is unprecedented and de-sirable.
Herein, a series of 2-acylbenzothiazole derivatives were synthesized for
the first time from the commercially available α-bromoacetophenones and
disulfanediyldianilines under the cooperation of ionic liquids and
microwave irradiation, metal- and ex-tra-additives-free conditions.
Significantly, the dialkylated [PMIM]I (PMIM = propyl methyl
imidazolium) ILs is utilized as the optimal al-ternatives for the
cyclization to furnish the 2-acylbenzothiazole and at least reused four
times without losing of the reaction activities. Furthermore,
thus-obtained products have been further converted to the desired
products via Suzuki and Sonogashira reaction. A plausi-ble mechanism
involved the successive ILs-induced enolation, radical addition,
intramolecular cyclization and MW-induced oxidative dehydrogenation was
also proposed. The simplicity and sustainability of MW-assisted
ILs-mediated reaction conditions for accessing functionalized
benzothiazoles is remarkable and could lead to many synthetic
innovations in biologically active molecules.