Synthesis of p-tert-Butyl-5,5'-bicalix[4]arene and Access to 5,5'-Bicalix[4] arenes Functionalized at the Upper Rim

Compound 1, a double p-tert-butylcalix[4]arene with direct para-para linkage, was obtained by FeCl3- mediated oxidative coupling of 5,11,17-tri-p-tert-butyl-26,27,28-tribenzoyloxycalix[4]arene-25-ol (4) followed by alkaline hydrolysis. With respect to the de-tert-butylated counterpart 1a, a different reactivity of 1 was observed in the NaH-promoted propylation, which gave octapropyl double-cone atropisomer 6 with higher stereoselectivity. Under competitive conditions 6 was selectively mononitrated at the biphenyl system, whereas ipso-nitration at t-Bubearing rings was obtained using a larger excess of HNO3.