Proximal O,O′-capped calix[4]arenes with a disiloxane bridge as highly efficient synthetic intermediates for 1,2-dialkylation at the lower rim

Treatment of calix[4]arenes with 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane using imidazole as a base yielded O,O′-bridged calixarenes in excellent yields, which were subsequently treated with an alkyl halide/base to give O″,O‴-dialkylated products in high yields. These were, in turn, amenable to fluoride-promoted quantitative desilylation, thus providing an efficient method for the net proximal dialkylation of calix[4]arenes at the lower rim.