The pyrene nucleus is a valuable component for materials, supramolecular and biological chemistry, due to its photophysical/electronic properties and extended rigid structure. However, its exploitation is hindered by the limited range of methods and outcomes for the direct substitution of pyrene itself. In response to this problem, a variety of indirect methods have been developed for preparing pyrenes with less usual substitution patterns. Herein we review these approaches, covering methods which involve reduced pyrenes, transannular ring closures and cyclisations of biphenyl intermediates. We also showcase the diverse range of substituted pyrenes which have been reported in the literature, and can serve as building blocks for new molecular architectures.
Bicyclic carbohydrate receptors are easier to synthesise than tri- or tetra-cyclic relatives, and are better adapted to bind monosaccharide residues with bulky appendages. Disaccharides containing β-glucosyl units are preferred substrates.
Transition-metal-catalyzed electrocyclic rearrangement of 2,6-diethynyl-1,1¢-biphenyl precursors to form polysubstituted pyrenes is described. This method is useful for the preparation of pyrenes with uncommon substitution patterns, and selective integration of functional groups at the 1-, 2-, 3-, 5-, 7-and 9-positions is demonstrated.
Pyrene-2-carboxylic acid is a versatile intermediate for introducing the unusual 2-pyrenyl unit into functional organic molecules. A classical preparation for this molecule has been revised and improved to give a robust and efficient three-step process. The method has been applied on a multigram scale to give pyrene-2-carboxylic acid in >70% overall yield from pyrene.
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