The Hexadehydro-Diels-Alder Reaction: A New Chapter in Aryne Chemistry

摘要

Arynes continue to stimulate new reactions and theoretical insight in aromatic chemistry. This has been driven in recent years by the exceptional versatility of 2-(trimethylsilyl)phenyl triflate (1) as a precursor to ortho-benzyne. Such compounds react under mild conditions and have enabled a substantial development of aryne chemistry both in terms of classical transformations (nucleophilic addition, pericyclic reactions) and in opening up new areas, such as σ-insertion reactions and transition-metal-catalyzed processes. As with all methods for the generation of ortho-benzyne to date, compound 1 requires the removal of two adjacent groups from a pre-existing arene. Recent work from the groups of Hoye and Lee has utilized a completely different approach to ortho-arynes, which proceeds through the intramolecular cycloaddition of triynes 3 (Scheme 1). This transformation, which was termed a hexadehydro-Diels-Alder (HDDA) reaction by Hoye in analogy to other dehydropericyclic reactions, is perhaps surprising at first glance because of the infrequently depicted aryne resonance structure 4, which immediately arises from the [4+2] cycloaddition. The trapping of an ortho-benzyne intermediate generated in this fashion can then be accomplished by a variety of inter- and intramolecular transformations, affording new approaches to valuable benzenoid compounds.