Synthesis and chemistry of frameworks with functional groups constrained on the face of aromatic rings.

Abstract

A unique family of U-shaped frameworks was constructed, having functional groups constrained to the face of an aromatic ring. These materials were then investigated neighboring interactions between the various functions and the aromatic system. The $\alpha,\alpha\sp\prime$ annelation of the enamine of the 1,3-dihydro-2-phenalenone with p-nitrostyrene quaternary salt (ETAC-I) affords a bicyclic framework, 9-endo-p-nitrophenyl-8,9,10,11-tetrahydro-7,11-methano-12-keto-7H-cycloocta (de) naphthalene, having two aromatic rings in an almost parallel-stacked geometry. The unique scaffold upon which the two aromatic rings were positioned was further engineered to add other units to create an alignment of the aromatic residues with an array of various functional groups (i. e. functional group 1 - aromatic shield - functional group 2). By using $\sp1$H NMR spectroscopy, this architecture was used for the study of the relay of through space orbital interactions. In addition, the functional groups on this new scaffold were manipulated to create new model systems, where the electron donor (p-N,N-dimethylaminophenyl) and electron acceptor (naphthyl) groups are separated by less than 4 A and are held in an almost parallel orientation. These molecular elements were designed for the study of intramolecular photoinduced electron transfer. In this study, the effects of solvent polarity, remote functional groups, and mutual orientation between electron donor and electron acceptor on the intensity and $\lambda$max of the charge transfer band were investigated. Through the application of $\alpha,\alpha\sp\prime$ annelation, the preparation of a second aromatic bicyclic framework was undertaken, methyl 8,9,10,11-tetrahydro-7,11-methano-12-keto-7H-cycloocta (de) naphthalene-9-endo-carboxylate. This compound has the carboxylic ester function positioned over the face of the aromatic ring. The close relationship of the carboxyl group with the face of the aromatic ring allows unique chemical interactions during electrophilic attack on the system. The acid derivatives of this framework dimerize affording a "sandwich" structure with the H-bonded carboxyl groups positioned between the parallel naphthalene rings. The effects of the dimeric association are easily probed using both NMR and fluorescence techniques. Synthesis of a molecular cleft, by employing the $\alpha,\alpha\sp\prime$ annelation reaction, was also attempted.