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. Keto­[n]­calixarenes
(n = 5, 6) were prepared via hydrolysis of the bromocalixarenes 11 and 12, followed by CrO3 oxidation
of the respective hydroxymethylene derivatives. Addition of MeLi to
the ketocalix­[n]­arenes (n = 4, 5
and 6) followed by elimination of water yielded the corresponding
calix­[n]­radialenes. Calix[5]- and calix[6]­radialenes
adopt in the crystal irregular alternate (i.e., noncone) conformations.