Enantioselective sensing using axially chiral diacridylnaphthalenes

We have developed the first synthetic route to highly congested, conformationally stable 1,8-diarylnaphthalenes using Pd-catalyzed Stille cross-coupling of 1,8-dibromonaphthalene and acridylstannanes in the presence of CuO. Screening of a wide range of Negishi, Kumada, Suzuki, Hiyama, and Stille cross-coupling procedures for the construction of 1,8-diarylnaphthalenes showed that superior results are obtained through palladium-catalyzed Stille coupling, in particular when undesirable alkyl transfer during transmetalation and dehalogenation can be controlled. 1,8-Diacridylnaphthalenes proved to be stable to syn/anti-isomerization even at high temperatures. Crystallographic and NMR, UV, and fluorescence spectroscopic studies showed that this class of compounds exhibits a rigid structure with two cofacial acridyl rings participating in face-to-face interactions.;The fluorescent diacridylnapthalenes prepared in our laboratory proved very useful for sensing of metal ions and enantiomers of various classes of compounds. We found that syn-1,8-di(4-isopropyl-9-acridyl)naphthalene undergoes highly Fe(III)-selective fluorescence quenching in aqueous solution even in the presence of excess of other metal ions. The fluorescence quenching was also found to be almost independent of counteranion effects.;Enantioselective recognition studies using 1,8-diacridylnapthalene-derived sensors showed stereoselective interactions with a variety of chiral compounds resulting in characteristic fluorescence changes. Fluorescence titration experiments using 1,8-bis(3-(3',5'-dimethylphenyl)-9-acridyl)naphthalene or its N,N'-dioxide revealed enantioselective formation of 1:1 or 1:2 complexes with amino acids and carboxylic acids. The high sensitivity inherent to fluorescence spectroscopy combined with the considerable enantioselectivity and broad application spectrum of this type of chemosensors affords a new tool for real-time analysis of the enantiomeric composition of chiral compounds. Atropisomeric 1,8-bis(3-(3',5'-dimethylphenyl)-9-acridyl)naphthalene N,N'-dioxide was found to effectively coordinate to a variety of metal ions, and the corresponding Sc(III) complex was successfully used for enantioselective recognition of a variety of chiral compounds such as amino acids, amino alcohols, and amines based on UV indicator-displacement assays.;1,8-Dipyridylnaphthalene was used as a template for highly stereoselective solid-state photodimerization of fumaric acid. Crystallization studies with acridine and its 9-halogenated derivatives resulted in the formation of two new polymorphs of acridine and a new dipolar acridone solid-state structure exhibiting second-order optical nonlinearity.