Incorporation of Three or Two Distal Double Bonds at the Methylene Bridges of the Calixarene Scaffold
datasetposted on 19.09.2014, 00:00 by Ori Shalev, Silvio E. Biali
Partial oxidation of the 1,3-alternate atropisomer of p-tert-butylcalixarene tetraacetate with CrO3 afforded mainly a mixture of trioxo- and tetraoxo-calixarene tetraacetate derivatives. The trioxotetrahydroxy derivative 6 was isolated from the mixture after hydrolysis of the crude product, followed by trituration with ethanol. Trioxocalixarene adopts in the crystal a 1,2-alternate conformation. Acetylation or alkylation of the tetrahydroxytrioxocalixarene 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 trioxocalixarenes followed by 3-fold elimination of water yielded calixarene derivatives possessing three exocyclic double bonds at the bridges. Reaction of the dioxotetramethoxy calixarene 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.