Fluoronaphthalene Building Blocks via Arynes: A Solution to the Problem of Positional Selectivity

Abstract When 3‐fluoro‐ and 3‐chloro‐1,2‐didehydrobenzenes are generated in the presence of 2‐(trimethylsilyl)furan, two regioisomeric cycloadducts are formed in a 1:2 ratio. However, regioselectivity can be installed by fitting one bulky trimethylsilyl group into sterically critical positions of each of the two reaction components. Thus 3‐fluoro‐6‐trimethylsilyl‐1,2‐didehydrobenzene and 2‐(trimethylsilyl)furan give one cycloadduct exclusively. In this way, the Diels–Alder reaction between suitably adorned arynes and similarly designed furans can open an entry to naphthalene derivatives that have unprecedented substituent patterns that qualify them as building blocks for pharmaceutical or agricultural research. The acid‐catalyzed isomerization of model 1,4‐epoxy‐1,4‐dihydronaphthalenes, the aryne/furan cycloadducts, exhibits unexpected effects on rates and regioselectivity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)