title: Incorporation of three or two distal double bonds at the methylene bridges of the calix[4]arene scaffold.
abstract: Partial oxidation of the 1,3-alternate atropisomer of p-tert-butylcalix[4]arene tetraacetate with CrO3 afforded mainly a mixture of trioxo- and tetraoxo-calix[4]arene tetraacetate derivatives. The trioxotetrahydroxy derivative 6 was isolated from the mixture after hydrolysis of the crude product, followed by trituration with ethanol. Trioxocalix[4]arene adopts in the crystal a 1,2-alternate conformation. Acetylation or alkylation of the tetrahydroxytrioxocalix[4]arene 6 with acetic anhydride and 1-bromobutane, respectively, afforded exclusively a single atropisomer of the product, which in both cases were characterized as the 1,3-alternate form. Addition of MeLi to the tetramethyl and tetrabutyl ether of the trioxocalix[4]arenes followed by 3-fold elimination of water yielded calixarene derivatives possessing three exocyclic double bonds at the bridges. Reaction of the dioxotetramethoxy calix[4]arene 9b with MeLi followed by 2-fold elimination of water afforded calixarene 11 with a pair of distal exocyclic double bonds at the bridges. Both the tetramethyl ether derivatives 9b and 11 exist in solution as a mixture of the 1,2-alternate and 1,3-alternate conformers, but in the crystal both adopt a 1,2-alternate conformation.
authors.affiliation: Institute of Chemistry, The Hebrew University of Jerusalem , Jerusalem 91904, Israel.
authors.forename: Ori
authors.initials: O
authors.lastname: Shalev
authors.forename: Silvio E
authors.initials: SE
authors.lastname: Biali