Novel Fenestranes Stitched Together

Using a one-pot procedure, chemists in France have developed a simple synthesis of complex [4.6.4.6]fenestradienes and [4.6.4.6]fenestrenes (J. Am. Chem. Soc., DOI: 10.1021/ja800691c). The efficient method provides rapid access to these unusual molecular scaffolds, which could be used as materials, ligands for catalysis, and pharmaceuticals. Named after the Latin word for window, fenestranes feature a windowpane-like structure in which four rings share a quaternary carbon. Building these polycycles' strained structures poses a challenge for synthetic chemists. Using a trienyne as their starting point, Jean Suffert, Catherine Hulot, and Gaëlle Blond of Louis Pasteur University of Strasbourg were able to design a cyclization cascade that assembles a [4.6.4.6]fenestrane skeleton with good yields (shown). In the key step, a nickel catalyst partially reduces the trienyne's triple bond. The researchers believe that the tetraene generated in this reaction undergoes an 8π-conrotatory electrocyclization followed by a 6π-disrotatory electrocyclization to form a [4.6.4.6]fenestradiene. This highly reactive compound (center) readily oxidizes in air to form a [4.6.4.6]fenestrene (right). "The high yields and the limited number of steps of the reaction sequence render this process very attractive for the synthesis of new fenestranes," the authors write.