Control of functional group proximity and direction by conformational networks: synthesis and stereodynamics of persubstituted arenes

The cooperative nonbonded interactions present in hexaethylbenzene result in an arrangement of alkyl groups such that the 1,3,5 and 2,4,6 substituents point to opposite faces of the benzene ring. Correspondingly, derivatives of hexaethylbenzene have their functional groups convergent (meta as in 1,3,5-trisubstituted-2,4,6-triethylbenzene) or divergent (ortho, para as in 1,2-disubstitnted-3,4,5,6-tetraethylbenzenes or 1,4-disubstituted-2,3,5,6-tetraethylbenzenes) due to this cooperative conformational network. To illustrate this structural feature and probe its dynamics, 1,4-di-X-2,3,5,6-tetraethylbenzenes have been synthesized. The dynamic stereochemistry of the disubstituted compounds has been studied by variable temperature H-1 NMR spectroscopy. Using the same strategy, the 1,3,5-tris(CH2Y)-2,3,6-triethylbenzenes have also been prepared. The steric bulk of the substituent in the disubstituted compounds has been found to influence the barrier height. The trends found are applicable for the use of these compounds as angular building blocks for the design of ligands, polymers, and supramolecular architectures. (C) 2001 Elsevier Science Ltd. All rights reserved.