Regio- and stereoselective alkylation of 5,5'-bicalix[4]arene. Access to double calixarenes with different conformations of the two subunits

Alkylation of 5,5'-bicalix[4]arene 1, a double calix[4]arene with direct para-para linkage, with PrI or p-tert-butylbenzyl bromide in the presence of various bases has been investigated. Good control of the regio- and stereochemical outcome was obtained, leading to the isolation of tetra-O- alkylated bicalix[4]arene derivatives 3-5 with syn-distal disubstitution at the two subunits and octa-O-alkylated atropisomers in double-cone 2, cone/partial-cone 6-8, double-1,3-alternate 9, and 1,3-alternate/partial- cone 10-12 conformations.