Efficient Iterative Synthesis of Oligophenylene Rods and Methodology Studies Involving Aryldiazonium Tetrafluoroborate Salts and Arylboronic Esters.

Abstract

Suzuki coupling protocols were applied towards the design and subsequent iterative synthesis of oligophenylene rods bearing polar functional groups. These well-defined, polar-functionalized rigid rods were ultimately constructed using an efficient iterative molecular doubling approach without using protecting groups, boronic acid isolations, Grignard or organolithium reactions or preparative chromatographic methods. Currently, these rods are being appended to resorcinarene macrocyclic scaffolds in efforts towards achieving a controlled synthesis of novel, uniform, three-dimensional, electronic directional materials with extended, highly functional lower aromatic cavities. Unique methodology studies involving aryldiazonium tetrafluoroborate salts and arylboronic esters were also contrived and investigated. A novel procedure for the direct, palladium-catalyzed cross-coupling reaction of aryldiazonium tetrafluoroborate salts with arylboronic esters to provide functionalized, unsymmetrical biaryls in moderate yields was developed. Various aryldiazonium tetrafluoroborate salts bearing both electron-donating and electron-withdrawing groups were evaluated at relatively mild temperatures and in aqueous media. Finally, a novel synthesis of arylboronic esters using bis(pinacolato)diboron and aryldiazonium tetrafluoroborate salts was also developed. The palladium-catalyzed borylation reaction proceeded efficiently under mild reaction conditions in the absence of base affording various functionalized arylboronic esters in moderate to high yields.