FULL PAPER DOI: 10.1002/ejoc.201000685 Synthesis and Molecular Structure of Symmetrical 1,8-Diarylnaphthalenes Grégory Pieters, [a] Vincent Terrasson, [a] Anne Gaucher,* [a] Damien Prim,* [a] and Jerôme Marrot [a] Keywords: Conformation analysis / N ligands / Palladium / Stacking interactions / Structure elucidation The synthesis of substituted 1,8-diarylnaphthalenes is re- ported. A bis-Suzuki coupling strategy starting from 1,8-di- bromonaphthalene provides a useful and general route to the 1,8-diarylnaphthalene scaffold. In this context, N-heterocy- clic benzhydrylamine ligands, in combination with PdCl 2 , were found to form especially efficient catalytic systems. The syn/anti ratios were determined in solution from their 1 H Introduction The 1,8-diarylnaphthalene scaffold is a fascinating exam- ple of unusual geometry in organic molecules. Introduction of two aromatic groups into both peri-positions of the naphthalene core causes severe repulsion between the stacked rings. This unique topology is not only due to the nature of the aromatics but also to the presence of ad- ditional substituents and their substitution pattern. [1] Gen- eration of steric compression at the rings, which are con- strained to face each other, may generate structural defor- mations such as non-planarity of the almost perpendicular naphthalene skeleton. [2] Since the first synthesis of 1,8- bis(2,2'-dimethyl-1,1'-diphenyl)naphthalene by Clough and Roberts, [3] several groups have described its syntheses and analyses, for example, the anti/syn isomerization of such motifs. [1a,4] Recently, some appealing applications have taken advantage of the difficult or impossible rotations of the aryl rings along the naphthalene axis. Indeed, 1,8-diac- ridyl-, 1,8-diquinolyl-, or 1,8-dipyridyl-naphthalenes have been developed as promising candidates for new photolumi- nescent or chiral sensors and stereodynamic switches. [1a,5] In addition, π-stacking between cofacial aromatics were found to be essential in 1,8-diarylnaphthalene-based non- linear optic chromophores or abiotic hydrid oligoamides. [6] Blue-transparent frequency-doubling devices incorporating thienyl, oligothienyl, or mixed pyridyl–thienyl branched naphthalenes have also been recently reported. [7] Strong π– [a] Institut Lavoisier de Versailles, Université de Versailles-Saint-Quentin-en-Yvelines, 45, Avenue des Etats-Unis, 78035 Versailles, France Fax: +33-1-39254452 E-mail: prim@chimie.uvsq.fr anne.gaucher@chimie.uvsq.fr Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejoc.201000685. View this journal online at wileyonlinelibrary.com © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Org. Chem. 2010, 5800–5806 5800 NMR spectra. Analysis of the molecular structure in the solid state for six new targets focused on deformation of the naph- thalene core. The observed lack of planarity occurs as a re- sult of several parameters, such as the nature and number of substituents, the substitution pattern as well as steric conges- tion and π-stacking between cofacial rings. π interactions have been characterized in cyclic oligophenyl- enes containing two 1,8-diarylnaphthalene subunits. [8] Co- facially arranged mono- or polymeric metal sandwich com- plexes have also attracted interest for their electrical, op- tical, and magnetic properties. [9] Moreover, the pillared 1,8- diarylnaphthalene motif has been used to elaborate cofacial salen-type ligands and their corresponding Mn com- plexes. [10] More recently, we described a short route to 6,11- diamino[6]carbohelicenes starting from 1,8-diarylnaphtha- lene. [11] Thus, steric and electronic interactions between two cofa- cial aromatics as well as the substitution pattern are not only essential to the aforementioned applications, but also deeply impact the preparation of 1,8-diarylnaphthalenes. Most of these molecules are obtained through metal-as- sisted carbon–carbon bond formation. Ni- and Cu- fol- lowed by Pd-based catalytic systems have successively been used to transform 1,8-dihalonaphthalenes into the expected 1,8-diarylnaphthalenes (Figure 1). [1–11,12] Figure 1. Metal-assisted preparation of 1,8-diarylnaphthalenes. These cross-coupling reactions, which have been reported to be sensitive to the nature and steric bulk of both part- ners, often afford mixtures of bis- or monocoupling prod- ucts. Suzuki- and Stille-type couplings are most commonly employed, with the latter being recently found to be supe- rior for highly congested partners. High yields in the cou-