An Efficient Synthetic Approach to Calix[ n ]furan[4‐ n ]pyrroles and the Calix[ n ]tetrahydrofuran[4‐ n ]pyrrolidines

A scalable synthesis of calix[ n ]furan[4‐ n ]pyrroles and their fully reduced analogues, calix[ n ]tetrahydrofuran[4‐ n ]pyrrolidines obtained by hydrogenation of their aromatic relatives, was developed and optimized. The hydrogenation reaction was studied at several selected pressures (P = 100, 50 and 15 bars) and high diastereoselectivity was observed for the four possible calix[ n ]tetrahydrofuran[4‐ n ]pyrrolidines. Moreover, two of the saturated macrocycles were obtained with good overall yields starting from easily accessible calix[4]furan. The conformation of the eight macrocycles was analyzed by X‐ray diffraction and although a classical 1,3‐alternate conformation of this type of compound was observed for the aromatic macrocycles, two distinct types of conformation were observed with the calix[ n ]tetrahydrofuran[4‐ n ]pyrrolidines.