Novel calixpyrrole-like anion receptors
Calix[n]pyrroles (n ≥ 4) are venerable anion receptors that are based on single pyrroles and ketones as building blocks. However, the existence of only one variable, n, that defines the nature of the systems, limits this class of macrocycles to only a few core structures. To overcome this limitation, a series of building blocks other than single pyrroles, have been applied to the construction of novel calixpyrrole-like systems. These building blocks include bipyrrole, furan, thiophene, and 1,3-bispyrrolylbenzenes. Based on bipyrrole as the sole building block, a series of calix[n]bipyrroles (n = 3, 4) was synthesized. Based on bipyrrole, furan or thiophene as co-building blocks, calixbipyrrole[m]furan[n]thiophene (m + n = 2) were obtained. Based on 1,3- bispyrrolylbenzenes, calix[n]bispyrrolylbenzenes (n = 2 - 4) were synthesized. These novel calixpyrrole-like macrocycles contain different core structures than calix[n]pyrroles, and thus display different anion binding properties than their parent systems. This, in turn, means that these new systems are not only helping to the chemistry of calixpyrroles, but also giving rise to selective receptors that find applications in anion coordination chemistry.