One-pot synthesis of p-tert-butylthiacalix[6/8]arenes

Since Miyano and co-workers' facile synthesis of p-tert-butylthiacalix[4]arene (1), many studies related to 1 have been published. In contrast, because of their extremely low yields, investigation of the larger macrocycles p-tert-butylthiacalix[6]arene (2) and p-tert-butylthiacalix[8]arene (3) has been limited. An improved synthetic method for 1-3 by the heating of p-tert-butylphenol, sulfur, and catalytic NaOH in a one-pot, two-stage procedure is described. The first step (oligomer formation) proceeds optimally at 180 degrees C for 24 h with 2 mol % NaOH. The second step (cyclization) is conducted at 230 degrees C with 50 mol % NaOH. Investigations by H-1 NMR spectroscopy and matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS) revealed that 2 and 3 transform into 1 and oligomers at the high temperature required for the cyclization step. Moreover, even 1 transforms into oligomers at high temperature for 48 h. Heating times of 5 and 24 h were optimal for the preparation of 2 (18.1 %) and 3 (4.6 %), respectively. A comparison of the thermal stability of the p-tert-butylthiacalix[n]arenes determined their stability in the order 1, 2, and 3.