Synthesis and structure of spirocyclic tetraethers derived from [1,1'-binaphthalene]-2,2'-diol and pentaerythritol

Molecular scaffolds that have well-defined geometries, are easy to synthesize and functionalize, and can hold attached sites of molecular recognition in suitable orientations are useful tools in various areas of science and technology. The utility of the tetraphenyl ether of pentaerythritol (4) as a scaffold in crystal engineering led us to study rigidified analogue SBINOX (5), the spirocyclic tetraether derived from pentaerythritol and [1,1'-binaphthalene]-2,2'-diol (BINOL). We have found that SBINOX (5) and derivatives can be prepared conveniently in acceptable yields and in stereoisomerically pure (S,S), (R,S), and (R,R) forms. X-ray crystallographic studies have revealed that the benzannulated 9-membered dioxonane rings in these structures adopt characteristic conformations of C1 symmetry. Intraannular C-H...O interactions help maintain the conformations of the individual rings, and the geometry of the spirocyclic SBINOX core is also controlled in part by distinctive short interannular C-H...O and C-H...pi interactions. Despite the inherent flexibility of the dioxonane rings, derivatives of SBINOX (5) can be expected to orient peripheral substituents in preferred ways, making SBINOX a potentially useful scaffold for applications in drug discovery, crystal engineering, and other fields.