Highly efficient synthesis of N-confused meso-tetraspirocyclohexyl calix[4]pyrrole using Brønsted acidic ionic liquids as catalysts

An efficient, green and novel protocol is described for high yield synthesis of N-confused meso-tetraspirocyclohexyl calix[4]pyrrole. In aqueous solution, the condensation of pyrrole and cyclohexanone in the presence of Brønsted acidic ionic liquid catalysts afforded N-confused calix[4]pyrrole in up to 62.5% yield which represents a ∼threefold yield improvement over existing protocol and makes significant quantity of N-confused calix[4]pyrrole readily available.