Calixradialenes: Calixarene Derivatives with Exocyclic Double Bonds

Reaction of dioxocalix[4]­arene <b>7</b> with MeLi followed by 2-fold elimination of water yielded calixarene <b>8</b> possessing exocyclic double bonds at two adjacent bridges. Calixarene <b>8</b> exists in tetrachloroethane-<i>d</i>₂ solution at rt, as a 2.3:1 mixture of the <i>1,3-alternate</i> and <i>partial cone</i> conformers. Keto­[<i>n</i>]­calixarenes (<i>n</i> = 5, 6) were prepared via hydrolysis of the bromocalixarenes <b>11</b> and <b>12</b>, followed by CrO₃ oxidation of the respective hydroxymethylene derivatives. Addition of MeLi to the ketocalix­[<i>n</i>]­arenes (<i>n</i> = 4, 5 and 6) followed by elimination of water yielded the corresponding calix­[<i>n</i>]­radialenes. Calix[5]- and calix[6]­radialenes adopt in the crystal irregular alternate (i.e., noncone) conformations