Ionic Liquid [PyN(CH2)4SO3H][CH3PhSO3] Mediated & Promoted Eco-Friendly One-Pot Domino Synthesis of Benzothiazolopyrano/Chromenopyrimidine Derivatives

Background: The pyridinium based p-toluenesulfonic acid functionalized [Py(CH2)4 SO3H][CH3PhSO3] ionic liquid has been employed as eco128;friendly solvent cum promoter for the multicomponent domino heterocyclization of substituted 2-aminobenzothiazoles with 4-hydroxy-6- methyl-2-pyrone / 4-hydroxycoumarin and aryl aldehydes to produce benzothiazolo[2,3-b]pyrano [3,4-e]pyrimidin-4-ones and benzothiazole [2,3-b]chromeno[3,4-e]pyrimidin-6-one in excellent yields. Methods and results: Three-component synthesis of structurally diverse benzothiazolopyrano/ chromenopyrimidines, incorporating the privileged heterocyclic scaffolds of medicinal relevance has been carried out by the reaction of substituted 2-aminobenzothiazoles with 4-hydroxy-6-methyl-2- pyrone / 4-hydroxycoumarin and aryl aldehydes in pyridinium based p-toluenesulfonic acid functionalized ionic liquid. The Brønsted acidic ionic liquid could be reused five-times without a significant loss of catalytic activity. Conclusion: The protocol proves to be efficient and facile in terms of high yields, operational simplicity, reduced reaction time and ease of recovery of the reaction medium.