A catalytic and solvent-free approach for the synthesis of diverse functionalized dipyrromethanes (DPMs) and calix[4]pyrroles (C4Ps)

Abstract

Needless to say, the development of green and sustainable reaction media instead of using volatile organic solvents as well as corrosive and/or expensive catalysts in the new millennium is continuously attracting great attention from the scientific community to meet the challenges of sheltering humanity and the environment while preserving commercial viability. In order to overcome the shortcomings of already existing environmentally hazardous and economically expensive synthetic protocols for the synthesis of diverse dipyrromethanes (DPMs) and calix[4]pyrroles (C4Ps), there is a supreme need to synthesize these valued supramolecular receptors under green conditions. Therefore, herein we report for the first time, a simple yet very effective green protocol for the construction of diverse functionalized DPMs and C4Ps in respectable yields without the involvement of an additional catalyst or a conventional organic solvent. In our study, a range of deep eutectic mixtures were tested, but a low melting point mixture of N,N′-dimethyl urea (DMU) and l-(+)-tartaric acid (TA) in the ratio of 7 : 3 at 70 °C was found to be the best choice. Interestingly, this method works equally well for large scale synthesis of these systems without significant reduction in the yields, which seems to be noteworthy from an industrial point of view.