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 sulfonat e esters including their conformational analysis were carried out. While p- tBu-calix[6]arene and p-tBu-calix[8]arene esters are conformationally labil e in the temperature interval of 25 -- 100 degrees C, p-tBu-calix[4]arene m ono- 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 conf ormational stability up to 100 degrees C by dynamic NMR measurements. The N MR measurements confirm the pinched-cone conformation for both derivatives. For the dealkylated calix[4]arene derivatives the partial cone conformer o f the triesters have been obtained as major products in all cases.