Synthetic and NMR studies on calix[n]arene (n = 4,6,8) triflates, mesylates, and tosylates

The synthesis and full characterization of eight new calix[n]arene sulfonate esters including their conformational analysis were carried out. While p-tBu-calix[6]arene and p-tBu-calix[8]arene esters are conformationally labile in the temperature interval of 25-100°C, p-tBu-calix[4]arene mono- and diesters were isolated as stable conformers at ambient temperature. Two 1,3-functionalised compounds of these derivatives, p-tert-butylcalix[4]arene ditriflate (5) and dimesylate (6) were shown unexpectedly high conformational stability up to 100°C by dynamic NMR measurements. The NMR measurements confirm the pinched-cone conformation for both derivatives. For the dealkylated calix[4]arene derivatives the partial cone conformer of the triesters have been obtained as major products in all cases.