Calixradialenes: calixarene derivatives with exocyclic double bonds.

Reaction of dioxocalix[4]arene 7 with MeLi followed by 2-fold elimination of water yielded calixarene 8 possessing exocyclic double bonds at two adjacent bridges. Calixarene 8 exists in tetrachloroethane-d2 solution at rt, as a 2.3:1 mixture of the 1,3-alternate and partial cone conformers.

Calix[4]arenes with two different chemical modifications at the bridges.

Hexabromocalix[4]arene derivatives (3a and 3b) possessing pairs of dibromomethylene and bromomethylene groups located at distal or proximal positions of the calix scaffold were prepared via photochemical bromination of tetramethoxycalix[4]arene. The dibromomethylene groups undergo hydrolysis to afford calix[4]arenes possessing pairs of carbonyl groups and bromomethylene groups located at distal or proximal bridges (4a and 4b, respectively). The bromomethylene groups of 4 undergo reactions with nucleophiles under S(N)1 conditions to afford a wide array of derivatives possessing two different chemical modifications at the bridges.

Restricted rotation of tert-butyl groups in sterically crowded methylene-functionalized calix[4]arenes.

The crowded methylene-functionalized calix[4]arenes 4 and 5 display restricted rotation of the tert-butyl substituents at the bridges. At low temperatures, separate signals were observed for the methyls of these groups in the (1)H NMR spectra.

Isotopic perturbation of the conformational equilibrium in methylene-functionalized calixarenes.

The 400 MHz 1H NMR spectrum of the tetramethoxycalixarene 2 (possessing hydroxyl groups at the bridges) in commercial acetone-d6 displays five signals (an isotopic multiplet) for a pair of methoxy groups. Inspection of the X-ray structures of 2 and its isomer 3 indicates that in the adopted 1,3-alternate conformation, the methoxy groups intramolecularly hydrogen bonded to neighboring OH groups are oriented "in" (pointing toward the cavity). Upon dissolution of 2 in acetone-d6, none, some, or all of the OH protons exchange with the deuterium atoms present in the residual water of the solvent.

Tetraaddition of PhLi to a ketocalixarene derivative.

[reaction: see text] Reaction of a ketocalixarene with 2.2 equiv or an excess of PhLi affords diaddition and tetraaddition products, respectively. Ionic hydrogenation of the tetraalcohol 8a yields a calix[4]arene monosubstituted by phenyl groups at all four methylene bridges.