syn-1,2-Dialkylated Calix[4]arene: General Intermediates in the NaH/DMF Tetraalkylation of Calix[4]arenes

In DMF or acetonitrile with NaH as a base at room temperature the tetraalkylation of calix[4]arenes 1a and 1b proceeds via the syn-1,2-disubstituted products to the tetraalkylated calix[4]arenes in the cone conformation. With KH as a base the tetraalkylated calix[4]arenes are predominantly formed in the partial cone conformation, and the reaction proceeds via both the syn-1,3-di and the syn-1,2-disubstituted products. Also the solvent influences the pathway via which tetraalkylation takes place. The syn-1,2-disubstituted calix[4]arenes 2-6 can be isolated in 15-55 % from the NaH/DMF or MeCN reactions when only 2.2 equiv of the electrophile are used.